Term
| Vascular Syndromes of the Pons |
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Definition
oAt caudal pontine levels, the territory of the paramedian branches of the basilar artery includes the exiting fibers of the abducens nerve, corticospinal fibers, and portions of the medial lemniscus
oOcclusion of the paramedical branches at caudal pontine levels results in an ipsilateral abducens nerve paralysis and a contralateral hemiparesis (the Foville syndrome) with a variable contralateral loss of proprioception, position, and vibratory sense reflecting various degree of damage to the medial lemniscus
oIf the lesion in the Foville syndrome extends into the pontine tegmentum, the patient may have additional deficits such as an ipsilateral horizontal gaze paralysis, indicating damage to the medial portions of the pontine reticular formation
oIf the area of damage is shifted somewhat laterally to involve corticospinal fibers and the root of the facial nerve, the patient has contralateral hemiparesis and an ipsilateral paralysis of the facial muscles (the Gubler or Millard-Gubler syndrome)
oAt midpontine levels occlusion of the paramedial and short circumferential branches results in the syndrome of the midpontine base; the main structures damaged and their respective deficits are:
1) Corticospinal fibers (contralateral hemiparesis)
2) Sensory and motor trigeminal roots (ipsilateral loss of pain and thermal sense in the face and paralysis of masticatory muscles)
3) Ataxia (fibers of the middle cerebellar peduncle)
oLesions within the pontine tegmentum may also combine cranial nerve signs and long tract signs e.g. lesion in the caudal pontine tegmentum may damage the abducens and facial nuclei (paralysis of the ipsilateral lateral rectus muscle and facial musculature) and the anterolateral system (contralateral loss of pain and thermal sense on the body)
oAt mid to more rostral pontine levels, damage to the tegmentum may involve the anterolateral system in combination with trigeminal motor nucleus and/or the sensory and motors roots of the trigeminal nerve
oAll examples are hallmark of brainstem vascular lesions-an ipsilateral cranial nerve sign coupled with contralateral tract sign
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Term
| Tumors of The Pineal Gland |
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Definition
oTumors of the pineal produce noncommunicating (obstructive) hydrocephalus because of compression of the colliculi or dorsal part of the midbrain (tectum) and resulting occlusion of the cerebral aqueduct |
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Term
| Lesions of The Crus Cerebri |
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Definition
oThe base of the midbrain on either side is formed by the basis pedunculi, which consists of the substantia nigra and the crus cerebri
oThe substantia nigra is related to motor functions
oThe crus cerebri contains corticospinal, corticonuclear (corticobulbar), and corticopontine fibers
oThe corticospinal and corticonuclear fiber populations are found in the middle third of the crus cerebri
oCorticospinal fibers projecting to the lumbosacral cord levels (lower extremity representation) are found laterally
oCorticonuclear fibers that project to cranial nerve nuclei (face representation) are located more medially
oCorticospinal fibers projecting to cervical cord levels (upper extremity representation) occupy an intermediate position
oCorticopontine fibers in the medial third of the crus arise from the frontal lobe (frontopontine), where as those in the lateral third originate from parietal (parietopontine), occipital (occipitopontine, and temporal (temporopontine) lobes
oLesions of the crus cerebri result in motor deficits related to the face and oral cavity and the body
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Term
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Definition
o The substantia nigra is functionally associated with the basal nuclei and is commonly divided into a compact part (pars compacta) and a reticular part (pars reticulate)
o Cells of the reticular part project to the superior colliculus, thalamus, and pontine reticular formation
o Cells of the pars compacta project diffusely to the caudate nucleus and putamen, where their synaptic terminals release dopamine
o Parkinson disease, a deficit characterized by tremor and difficulty in initiation or terminating movement, is associated with the loss of dopamine-containing cells in the pars compacta |
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Term
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Definition
Occlusion of the vessels serving the medial portions of the midbrain
Ipsilateral paralysis of all extraocular muscles except the lateral rectus and superior oblique, reflecting damage to the exiting root of the oculomotor nerve
Paralysis of the contralateral extremities, indicating damage to the corticospinal fibers in the crus cerebri
Ipsilateral pupil is dilated
Weakness of the facial muscles of the lower half of the face on the side contralateral to the lesion, reflecting damage to the corticonuclear fibers in the crus
Deviation of the tongue when protruded on the side contralateral to the lesion, reflecting damage to the corticonuclear fibers in the crus |
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Term
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Definition
Vascular lesion located in the more central area of the midbrain
Damage to fibers of the oculomotor nerve results in ipsilateral paralysis of most eye movements: the eye is directed down and out with a dilated pupil
Damage to red nucleus and cerebellothalamic results in contralateral ataxia, tremor, and incoordination |
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Term
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Definition
A large lesion that includes the territories of both the Weber and Claude syndromes
Ipsilateral paralysis of most eye movements, contralateral weakness of the extremities, and contralateral tremor and ataxia
o In each of these lesions it is possible that the GVE preganglionic parasympathetic fibers arising in the Edinger-Westphal nucleus may be damaged-the pupil on the side of the lesion will be dilated due to the action of the intact sympathetic input to the dilator muscle of the iris |
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Term
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Definition
o Central (or transtentorial) herniation may follow a large hemorrhage into the hemisphere or a large rapidly growing tumor
o Essentially the enlarging mass forces the diencephalon downward through the tentorial incisure and into the midbrain
o Prior to the herniation the patient is less alert (decreased level of consciousness) and may have altered respiratory patterns and eye movements
o The patient responds to noxious stimuli but will have hyperactive muscle stretch reflexes
o As intracranial pressure increases, the patient may become decorticate (lower extremities, trunk, and neck extended; upper extremities flexed)
o The herniation traverses the tentorial notch and impinges on the midbrain
o The patient is comatose, pupils are dilated and fixed, and respiration is irregular with changes in depth and rate (Cheyne-Stokes) or periods of tachypnea and eventual apnea; the patient becomes decerebrate with all four extremities extended
o As the cone of ischemia extends into, and through, the midbrain the deficits are exacerbated and the likelihood of survival is greatly diminished |
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Term
| Upward Cerebellar Herniation |
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Definition
o Upward cerebellar herniation may result from an expanding mass in the posterior fossa
o Medial portions of the cerebellum pass upward through the tentorial notch and compress the midbrain
o There is the eventual possibility of cerebellar infarction from compression of the superior cerebellar arteries and hydrocephalus from obstruction of the cerebral aqueduct
o Usually has a good outcome if the primary cause of the herniation is treated in a timely manner |
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Term
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Definition
o Uncal herniation results from an expanding lesion (usually hematoma) in the hemisphere, frequently the temporal lobe, that forces the uncus over the edge of the tentorium and into the midbrain
o Initial finding is a dilated pupil (pressure on the third nerve) on the side of the herniation followed by a paralysis of most eye movement in the eye with the dilated pupil
o As the herniation progresses, corticospinal fibers in the crus cerebri are compressed, resulting in weakness of the contralateral upper and lower extremities
o Cranial nerve signs such as (1)central seven (lower facial muscles contralaterally), (2)difficulty swallowing, and (3)deviation of the tongue contralaterally on protrusion may also appear as a result of damage to corticonuclear fibers in the crus cerebri
o If cause of herniation is not treated, deficits may escalate into those described for central herniation with similar consequences |
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Term
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Definition
o Occlusion of the penetrating branches of the anterior artery (as in the medial medullary syndrome) may result in paralysis of the genioglossus muscle with deviation of the tongue toward the side of the lesion (the weak side) on protrusion
o In addition, the patient experiences a contralateral hemiparesis (corticospinal tract) and a contralateral loss of position sense, vibratory sense, and two-point discrimination (medial lemniscus)
o Other lesions that may affect hypoglossal function include a lesion of the root of the nerve only (causing tongue deviation to the side of the lesion with no other deficits)
o Injury to the internal capsule results in deviation of the tongue to the contralateral side (opposite to the lesion) on protrusion due to damage to the crossing corticonuclear (corticobulbar) fibers to the hypoglossal motor neurons innervating the genioglossus, in concert with other deficits such as contralateral hemiplegia and drooping of the facial muscles in the lower quadrant of the contralateral side of the face |
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Term
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Definition
o This so-called cranial nerve was historically described as having a cranial part (from the medulla) and a spinal part (from the cervical spinal cord)
o Experimental studies have shown that the neurons that innervate the sternocleidomastoid and trapezius muscles are located in the cervical cord only; these muscles are not innervated by motor neurons located in the medulla
o The accessory nerve is considered here as a cranial nerve for consistency and in recognition of wide usage
o The accessory nerve originates from motor neurons in the cervical spinal cord
o Axons exit the lateral aspect of the cord, coalesce to form the nerve, ascend to enter the cranial cavity via the foramen magnum, and exit the posterior fossa through the jugular foramen
o En route through the posterior fossa these fibers briefly join the caudal portions of the vagus nerve and then leave the vagus to exit the skull as the accessory nerve; it is this temporary apposition of vagus fibers to the intracranial portion of the accessory nerve that was originally interpreted as the so-called cranial part of the accessory nerve
o The relationship of the accessory nerve to the vagus nerve is similar to the relationship of the facial nerve to the trigeminal nerve via the chorda tympani
1) Taste fibers from the anterior two thirds of the tongue travel on the trigeminal nerve and then join the facial nerve via the chorda tympani; throughout their extend, these taste fibers are considered as part of the facial nerve, not the trigeminal
2) Fibers of the accessory nerve temporarily join the vagus and then leave it to exit the skull; these accessory fibers do not originate from the medulla, do not distribute peripherally with the vagus, and have their cells of origin in the cervical spinal cord
o What has classically been called the cranial part of the accessory nerve is a misnomer; these fibers are the caudal portions of the vagus nerve to which the accessory nerve temporarily related
o Reflecting the fact that the sternocleidomastoid and trapezius muscles in the human originate from the mesoderm caudal to the fourth arch (not in the fourth arch), the functional component associated with these motor neurons is GSE
o Lesions of the root of the accessory nerve result in drooping of the shoulder (trapezius paralysis) on the ipsilateral side and difficulty in turning the head to the contralateral side (sternocleidomastoid paralysis) against resistance
o Weakness of these muscles is not especially obvious in cervical cord lesions, because a hemiplegia (damage to the corticospinal fibers) is the overwhelmingly obvious deficit
o Lesion to the internal capsule may also result in deficits similar to those described previously, owing to interruption of the corticonuclear (corticobulbar) fibers to the accessory nucleus, these corticonuclear fibers are primarily uncrossed |
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Term
| •• Glossopharyngeal Nerve |
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Definition
o Lesions of the ninth cranial nerve are relatively rare but may occur in combination with the vagal and accessory roots at the jugular foramen
o Deficits related only to glossopharyngeal nerve damage are largely restricted to a loss of taste from the posterior one third of the tongue and a loss of the gag reflex on the side of the lesion in which both sensory and motor limbs of the reflex are affected
o CN IX is subject to glossopharyngeal neuralgia which is characterized by attacks of intense idiopathic pain arising from the GVA sensory distribution of the nerve (pharynx, caudal parts of the tongue, tonsil, and possibly areas of the middle ear); the attacks may be spontaneous or may result from artificial stimulation of the back of the oral cavity or from swallowing or even talking |
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Term
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Definition
o Lesion of the root of the vagus nerve will result in…
1) Dysphagia(trouble swallowing), owing to the unilateral paralysis of pharyngeal and laryngeal musculature
2) Dysarthria(trouble speaking), owing to a weakness of the laryngeal muscles and the vocalis muscles; may be seen in patients after thyroid surgery if the recurrent laryngeal nerve has been damaged
o Unilateral injury inside the medulla, as with tumors, vascular lesions, or syringobulbia, medullary syndrome, may give rise to dysphagia and dysarthria due to damage to the nucleus ambiguus
o There are no lasting demonstrable symptoms specifically related to visceromotor (autonomic dysfunction), taste loss is not detectable and cannot be tested, and the small somatosensory (GSA) loss involving the external auditory meatus and canal is usually of no consequence
o Bilateral lesions of the medulla, although rare, result in aphonia, aphagia, dyspnea, or inspiratory stridor; such lesions may be life threatening, especially if they involve the dorsal motor nucleus |
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Term
| • Syndromes of The Jugular Foramen |
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Definition
o Deficits seen in jugular foramen syndromes reflect damage to the contents of the foramen or to structures immediately external the foramen
o Syndrome of the jugular foramen (aka Vernet syndrome) is usually caused by a lesion at, or immediately internal to, the foramen
o These deficits are:
1) Loss of sensation (including taste) in the posterior third of the tongue (CN IX)
2) Loss of sensations in the larynx and pharynx, dysarthria and dysphagia resulting from paralysis of the vocal fold and muscles of the throat on the ipsilateral side (CN X)
3) Weakness of the ipsilateral sternocleidomastoid and trapezius muscles (CN XI)
o Lesions immediately external to the jugular foramen (as in the Collet-Sicard syndrome) result in deficits characteristic of damage to CN IX, X, XI plus weakness of the tongue on the side of the lesion because the exit of the hypoglossal nerve (via hypoglossal canal) is adjacent to the jugular foramen and the root of this nerve is recruited into the lesion
o The most inclusive syndrome of the jugular foramen is Villaret syndrome, which includes deficit that are indicative of damage to CN IX, X, and XI, the hypoglossal nerve, and sympathetic fibers of the superior cervical ganglion, the last producing a Horner syndrome on the ipsilateral side of the head |
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Term
| • Vestibulocochlear Nerve |
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Definition
o Lesions of the vestibulocochlear nerve may result from a wide range of causes
o The clinical manifestations include (1)hearing loss, (2)tinnitus, (3)vertigo, (4)dizziness, (5)related problems such as ataxia
o Injury to the cochlea, spinal ganglion, or cochlear fibers in CN VIII result in loss of hearing on the side of the lesion; this type of hearing loss is sensorineural hearing loss
o Lesions within the brainstem or at higher levels may affect the patient’s ability to precisely interpret or to localize a sound in space, but such lesions do not result in deafness in one ear
o Conductive hearing loss results from a failure of conduction through the middle ear, usually involving the ossicles
o Tinnitus is a ringing, hissing, or roaring sensation perceived by the patient; it is related to the auditory part of CN VIII and may result from injury to the peripheral part of the nerve or may follow central lesions that damage auditory fibers or structures
o Injury to the vestibular fibers of CN VIII results in vertigo (a perception of movement) and nystagmus that may be accompanied by nausea and vomiting
o The vertigo may be subjective (patient perceives that his or her body is moving) or objective (the patient perceives that objects in the environment are moving)
o Nystagmus (rhythmic oscillatory movements of the eyes) results from the interruption of vestibular influence over the brainstem motor neurons controlling eye movement, and the nausea and vomiting are a natural consequence of the disconnection between body or eye movements and the environment
o Lesions of the vestibular nuclei and their main central connections, especially the cerebellum, result in (1)a sensation of spinning called vertigo (subjective vertigo-the patient sense that he or she is moving; objective vertigo-the patient perceives that objects in the environment are moving), (2)ataxia and unsteady gait (the patient feels that his or her “balance is off”), and (3)nystagmus; these signs and symptoms may range from mild to severe and may be accompanied by nausea and vomiting
o Sign and symptoms of vestibular dysfunction may result from a wide range of causes such as toxicity from (1)certain medications, (2)trauma, (3)diabetes, (4)cerebellar lesions, and (5)acoustic neuroma
o Meniere syndrome is characterized by hearing loss and sound distortion as well as vertigo and a sensation of dizziness or unsteadiness on walking or standing; the cause is unknown, but there seems to be an increase in endolymphatic pressure with an increase in size of the utricle, saccule, and cochlear duct |
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Term
| • Lesions in The Cerebellopontine Angle |
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Definition
o The vast majority of lesions found at this site are vestibular schwannomas (85%), meningiomas (5% to 10%), or epidermoid tumors (5%)
o Vestibular schwannomas, tumors originating from Schwann cells of the vestibular root, are sometimes incorrectly called acoustic neuromas
The deficits associated with this tumor are initially (1)tinnitus, (2)unsteady gait, and (3)progressive loss of hearing in that ear (as the tumor enlarges and impinges on the acoustic root), with a weakness of ipsilateral facial muscles appearing in later stages
If very large (greater than 3 cm), vestibular schwannomas may impinge on the root of the trigeminal nerve and also produce sensory deficits and/or pain sensation similar to tic douloureux
o Meningiomas may arise from the margins of the internal acoustic meatus (frequently the anterior or superior edges) and result in a facial weakness early followed later by hearing loss and pain related to involvement of the trigeminal root
Meningioma may erode and slightly enlarge the internal acoustic meatus, significant enlargement of this opening is a feature more commonly seen in the CT scan of patients with a vestibular schwannoma
o Epidermoid tumors (also called epidermoid cysts or cholesteatoma) arise from clusters of epidermis that are entrapped during development and give rise to a benign slow-growing lesion
Epidermoid tumors are commonly lined with an epithelium and contain cellular debris, proteins, and cholesterol
Spillage of the cyst contents may cause recurrent bouts of aseptic meningitis
o Although relatively rare, these lesions may be found anywhere in the CNS; when found at the cerebellopontine angle, they cause deficits reflecting damage to CN V, VII, and VIII |
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Term
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Definition
o Lesions of the efferent fibers from the face motor cortex or of the internal capsule (spuranuclear) result in drooping or sagging of the corner of the mouth contralateral to the lesion when the patient is asked to smile voluntarily; such lesions are referred to as central seven lesions
o Although some patients cannot smile when asked to do so, they can sometimes smile “involuntarily” or spontaneously in response to an amusing comment or situation
o Signs and symptoms due to peripheral lesions of the facial nerve (infranuclear; lower motor neurons) depend on the location of the damage
o If the injury occurs proximal to the geniculate ganglion and the origin of the greater petrosal nerve, the patient exhibits a loss of voluntary control of ipsilateral facial expression muscles in the upper and lower portions of the face
This motor (the Bell palsy) deficit is accompanied by decreased mucosal secretion in the nasal and oral cavities and decreased tear fluid production and salivary gland output, all on the ipsilateral side
Cutaneous sensation of the external ear and external auditory canal is also diminished, but innervations of this territory is difficult to assess because CN IX and X contribute as well
In addition, there is decreased taste sensation (SVA) on the anterior two thirds of the tongue (but general sensation on the face, GSA, is preserved) and hyperacusis on the side ipsilateral to the lesion
o If the lesion occurs distal to the ganglion but proximal to the origin of the chorda tympani and stapedial nerve, decreased salivation and taste and hyperacusis may be present in conjunction with decreased facial expression throughout the ipsilateral side of the face
Tear fluid production and the mucosal surfaces of the nasal and oral cavities are unaffected because the greater petrosal nerve is intact
o Decreased function of all facial expression muscles on one side of the face in combination with the absence of any deficits involving parasympathetic function or the sense of taste serves to localize the lesion at, or distal, the stylomastoid foramen
o Bilateral paralysis of the facial muscles, facial diplegia, may been seen in congenital conditions such as myotonic muscular dystrophy or in the Mobius syndrome which has complex congenital defects that affect movements of the face and eyes (due to partial agenesis these respective nuclei) and cause defects of the extremities and skeleton
The bilateral facial weakness in the Mobius syndrome frequently affects the upper portions of the face more than the lower portions or the whole face
o Facial diplegia is also seen in patients with Lyme disease, in those with the Guillain-Barre syndrome (50% of fatal cases will have this feature), or in patients who may have botulism poisoning or infection with Corynebacterium diphtheriae
o Hemifacial spasm are irregular, and sometimes painful, contractions of the facial muscles that may be triggered by voluntary movements of the facial muscles
While etiology is unknown in some cases, hemifacial spasm may follow and episode of Bell palsy or result from compression of the root of the facial nerve by a lesion or vessel such as branches of the anterior inferior cerebellar artery |
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Term
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Definition
o Lesions of the medial longitudinal fasciculus from interneurons in the abducens lead to the clinical condition known as internuclear ophthalmoplegia
o Lesions of the abducens nerve, the abducens nucleus, or the internuclear axons in the medial longitudinal fasciculus have similar, yet individually unique features
o Injury to the abducens fibers in the pons (medial pontine syndrome) or in its course outside the brain results in a flaccid paralysis of the ipsilateral lateral rectus muscle; the affected eye is slightly introverted and does not abduct on the attempted lateral gaze to that side; the opposite eye adducts because the internuclear neurons are intact
o A lesion of the abducens nucleus, such as the fourth ventricle tumor invading the facial colliculus, damages both the motor neurons and the internuclear neurons; the result is paralysis of the lateral rectus muscle on the side of the lesion accompanied by failure of the opposite medial rectus muscle to contract on attempted gaze toward the side of the lesion
o Damage only to the internuclear axons in the left medial longitudinal fasciculus (multiple sclerosis) results in an inability to adduct the left eye on attempted gaze to the right
o In contrast, with lesions of the left abducens nucleus or nerve, the right eye can abduct, because the motor neurons in the right nucleus and their axons are intact
o An extension of a lesion involving the abducens nucleus resulting in weakness of the ipsilateral lateral rectus muscle and the contralateral medial rectus muscle is seen in a lesion that involves the abducens nucleus and fibers of the immediately adjacent medial longitudinal fasciculus, resulting in the one-and-a-half syndrome
o Sudden cortical damage (stroke or trauma) involving the frontal eye field results in an involuntary conjugate deviation of the eyes to the side of the lesion |
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Term
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Definition
o The primary deficits in patients with lesions of the trigeminal nerve, or its central nuclei, are sensory symptoms in the peripheral distribution of the nerve (or its individual division) and paralysis of the masticatory muscles
o The sensory deficits are a (1)complete loss of pain, thermal, and tactile sensations on the ipsilateral side of the face and much of the scalp, (2)a loss of the same sensations in the oral cavity (and from the teeth) on the same side, and (3)a loss of the corneal reflex occurring in response to corneal touch, also on the same side
o An injury to one trigeminal nerve does not cause a loss of the jaw jerk reflex
o Another sensory disorder associated with the trigeminal nerve is tic douloureux (trigeminal neuralgia)
This condition is characterized by severe, unexpected, lancinating pain restricted to one or more of the divisions of the nerve
Paroxysms of intense pain may result from stimulation of a trigger zone frequently located around the lip or nose or on the cheek
A wide variety of stimuli such as shaving, putting on makeup, talking, chewing, eating, a breeze on the face, or a sudden facial expression may precipitate an attack
Some patients may become malnourished because they avoid eating, chewing, and swallowing for fear of an attack
Trigeminal neuralgia is seen more frequently in patients older than 35 years of age, usually involves the maxillary division more often than the mandibular (second most commonly involved) or ophthalmic (rarely involved) division, and can severely compromise the quality of life
Trigeminal neuralgia may be seen in patients with multiple sclerosis, degenerative changes in the trigeminal ganglion, or vascular malformations
Compression of the trigeminal nerve root by aberrant vessels, usually branches of the superior cerebellar artery, is one known cause of trigeminal neuralgia
At autopsy, some people have what appears to be compression of the trigeminal root but did not exhibit symptoms of trigeminal neuralgia
o Motor deficits resulting from trigeminal root lesions result in paralysis of the masticatory muscles on that side
The patient has difficulty chewing food, and the jaw deviates toward the side of the lesion (weak side) on closing; this deviation occurs because of the unopposed action (pull of the mandible toward the midline) of the pterygoid muscles on the opposite (undamaged) side
Although relatively rare, some patients with trigeminal neuralgia also experience status trigeminus, which are tick-like contractions of the masticatory muscles
o Sensory or motor deficits related to the trigeminal nerve can also occur from central lesions; such lesions include, but are not limited to, (1)tumors or (2)vascular lesions in the medulla or pons, (3)metastatic lesions, and the (4)obstruction of vessels
o A well-known example of a lesion due to vascular obstruction is the lateral medullary syndrome (also called posterior inferior cerebellar artery syndrome or Wallenberg syndrome), in which there is an alternating sensory loss
Wallenberg syndrome results in an ipsilateral loss of pain and thermal sense on the face (spinal trigeminal tract) and a contralateral loss of the same sensations on the body (anterolateral system), in concert with motor deficits most frequently related to damage to the nucleus ambiguus or vestibular nuclei |
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Term
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Definition
o A lesion at the root of the nerve in the ambient cistern or cavernous sinus, or at the superior orbital fissure, results in paralysis of the superior oblique muscle on that side
o If the lesion is on the left side, the left eye cannot rotate slightly downward and outward
o In patients with multiple sclerosis involving the MLF, the damage to which has extended to the trochlear nucleus, a variation on this theme may been seen
o A lesion in the right MLF with trochlear nucleus involvement results in paralysis of the left superior oblique muscle, and the left eye cannot rotate downward and outward to the left; in clear contrast to trochlear nerve root lesion, the patient also has internuclear ophthalmoplegia on the right
o Sudden cortical damage (such as from stroke or trauma) involving the frontal eye field results in an involuntary conjugate deviation of the eyes to the side of the lesion |
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Term
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Definition
o Cortical damage (such as from stroke or trauma) involving the frontal eye fields produces an involuntary conjugate deviation of the eyes toward the side of the injury; the patient “involuntarily looks to the lesioned side”
o If the cortical lesion is large enough to involve the corticospinal fibers, the deviation of the eyes is toward the side of the cortical damage but away from the side of the resulting hemiparesis
o Lesions involving the oculomotor nucleus, the oculomotor nerve in the interpeduncular cistern, or the nerve in the lateral wall of the cavernous sinus all generally have the same result
o Loss of the GSE motor fibers paralyzes all of the extraocular muscles in the ipsilateral orbit except the superior oblique and lateral rectus muscles; as a result, the ipsilateral eye assumes an abducted and depressed position (down and out), owing to the unopposed action of the lateral rectus and superior oblique muscles
o The patient also experiences diplopia (double vision) because the image seen by each eye cannot be directed to corresponding portions of each retina, as most of the extraocular muscles in one eye are not functional
o Interruption of the preganglionic parasympathetic fibers in the oculomotor nerve results in characteristic signs and symptoms in the ipsilateral eye:
1) The pupil is dilated (mydriasis) and nonreactive to light because the sphincter pupillae muscle is denervated (the dilator pupillae muscle, innervated by sympathetic fibers, is intact)
2) The lens in the ipsilateral eye cannot accommodate because the ciliary muscle is also denervated
3) Although the innervation to the superior tarsal muscle is intact because the course of the sympathetic fibers does not involve the oculomotor nerve outside the orbit, the upper eyelid exhibits ptosis (droop) because the levator palpebrae has been denervated by the oculomotor nerve lesion
o Because the parasympathetic fibers are located near the periphery (outer surface) of the oculomotor nerve, visceromotor signs and symptoms such as subtle ptosis or medley diminished pupil reactivity can appear before the onset of, or in the absence of, any extraocular muscle dysfunction with external compressive injury to the oculomotor nerve
o The external compression affects the superficially located, smaller-diameter visceromotor fibers first
o In contrast, in diabetic patients, the onset of an eye movement disorder may not be accompanied by visceromotor signs and symptoms; this is because diabetes is a vascular problem and the larger vessels inside the nerve are compromised first, thereby affecting the internally located, larger-diameter GSE motor axons but sparing the smaller and more superficially located visceromotor fibers
o Isolated lesions of the oculomotor nerve distal to its passage through the superior orbital fissure are relatively rare and produce variable symptoms depending on the location of the lesion |
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Term
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Definition
o Cortical damage (such as from stroke or trauma) involving the frontal eye fields produces an involuntary conjugate deviation of the eyes toward the side of the injury; the patient “involuntarily looks to the lesioned side”
o If the cortical lesion is large enough to involve the corticospinal fibers, the deviation of the eyes is toward the side of the cortical damage but away from the side of the resulting hemiparesis
o Lesions involving the oculomotor nucleus, the oculomotor nerve in the interpeduncular cistern, or the nerve in the lateral wall of the cavernous sinus all generally have the same result
o Loss of the GSE motor fibers paralyzes all of the extraocular muscles in the ipsilateral orbit except the superior oblique and lateral rectus muscles; as a result, the ipsilateral eye assumes an abducted and depressed position (down and out), owing to the unopposed action of the lateral rectus and superior oblique muscles
o The patient also experiences diplopia (double vision) because the image seen by each eye cannot be directed to corresponding portions of each retina, as most of the extraocular muscles in one eye are not functional
o Interruption of the preganglionic parasympathetic fibers in the oculomotor nerve results in characteristic signs and symptoms in the ipsilateral eye:
1) The pupil is dilated (mydriasis) and nonreactive to light because the sphincter pupillae muscle is denervated (the dilator pupillae muscle, innervated by sympathetic fibers, is intact)
2) The lens in the ipsilateral eye cannot accommodate because the ciliary muscle is also denervated
3) Although the innervation to the superior tarsal muscle is intact because the course of the sympathetic fibers does not involve the oculomotor nerve outside the orbit, the upper eyelid exhibits ptosis (droop) because the levator palpebrae has been denervated by the oculomotor nerve lesion
o Because the parasympathetic fibers are located near the periphery (outer surface) of the oculomotor nerve, visceromotor signs and symptoms such as subtle ptosis or medley diminished pupil reactivity can appear before the onset of, or in the absence of, any extraocular muscle dysfunction with external compressive injury to the oculomotor nerve
o The external compression affects the superficially located, smaller-diameter visceromotor fibers first
o In contrast, in diabetic patients, the onset of an eye movement disorder may not be accompanied by visceromotor signs and symptoms; this is because diabetes is a vascular problem and the larger vessels inside the nerve are compromised first, thereby affecting the internally located, larger-diameter GSE motor axons but sparing the smaller and more superficially located visceromotor fibers
o Isolated lesions of the oculomotor nerve distal to its passage through the superior orbital fissure are relatively rare and produce variable symptoms depending on the location of the lesion |
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Term
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Definition
o The development of the pituitary gland during the third week is linked to that of the diencephalon
o A downward extension of the floor of the third ventricle, the infundibulum, meets the Rathke pouch, an upward outpocketing of the stomodeum, the primitive oral cavity
o By the end of the second month, the Rathke pouch loses its connection with the developing oral cavity but maintains its attachment to the infundibulum
o As development continues, the Rathke pouch gives rise to the anterior lobe (adenohypophysis) and pars intermedia of the pituitary gland, whereas the infundibulum differentiates into the posterior lobe of the pituitary gland, or neurohypophysis
o A craniopharyngioma (Rathke pouch tumor) can rise from a portion of the Rathke pouch that fails to undergo proper migration and apposition to the infundibulum
o These tumors mimic lesions of the pituitary and may cause visual problems, diabetes insipidus, and increased intracranial pressure |
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Term
| • Ventral Posterior Nucleus of Thalamus |
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Definition
o The ventral posterior nucleus, consisting of ventral posterolateral (VPL) and ventral posteromedial (VPM) nuclei, conveys somatosensory information to the cerebral cortex from the contralateral sides of the body
o Both the VPL and VPM project to the somatosensory cortex of the parietal lobe
o Lesions of the VPL will most directly affect the relay of somatosensory information from the body to the primary somatosensory cortex
o A small vascular lesion that damages the VPM will interrupt the transmission of somatosensory information from the face to the somatosensory cortex |
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Term
| • Ventral Lateral Nucleus of Thalamus |
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Definition
o The ventral lateral (VL) nucleus of the thalamus are important motor-related nuclei
o The VL is also composed of three subdivisions: (1)pars oralis, (2)pars medialis, (3)pars caudalis
o The largest, pars oralis, receives a dense projection from the internal segment of the ipsilateral globus pallidus; some of these afferents enter the caudal subdivision
o In contrast, the pars caudalis subdivision of the VL receives its main input from the contralateral cerebellar nuclei
o The output of the VL reflects its segregated input in that the oral and caudal parts project to largely separate areas of the frontal lobe
o Damage to the VL will most specifically affect the efficacy of motor activity |
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Term
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Definition
o The lateral (LGB) and medial (MGB) geniculate nuclei are considered parts of the lateral thalamic nuclear group
o The medial geniculate nucleus receives ascending auditory input via the brachium of the inferior colliculus and projects to the primary auditory cortex in the temporal lobe
o The lateral geniculate nucleus receives visual input from the retina via the optic tract and in turn projects to the primary visual cortex on the medial surface of the occipital lobe
o Lesions of the lateral geniculate nucleus will result in a partial loss of vision |
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Term
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Definition
o Unlike the thalamus, which is primarily related to somatic functions, the hypothalamus is mainly involved in visceromotor, viscerosensory, and endocrine activities
o Damage to the hypothalamus will result in a variety of visceromotor dysfunctions
o Hypothalamic lesions may affect sleep-wake cycles, eating behavior, the ability to maintain body temperature, activity of a variety of releasing hormones, and other visceral activities |
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Term
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Definition
o The cells of the subthalamic nucleus receive input from the motor areas of the cerebral cortex, project to the substantia nigra, and are reciprocally connected with the globus pallidus
o The subthalamic nucleus can be affected by vascular lesions involving posteromedial branches of the posterior cerebral or posterior communicating arteries, which results in a clinical condition known as hemiballismus
o Patients with this involuntary movement disorder exhibit rapid and forceful flailing movements, which usually involve the contralateral upper extremity
o These movements can be very debilitating because the patient has no control over their initiation or duration |
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Term
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Definition
o Pinealocytes also produce serotonin, norepinephrine, and neuroactive peptides, such as thyrotropin-releasing hormone (TRH), which are normally associated with the hypothalamus
o Pinealomas (tumors with large numbers of pinealocytes) are accompanied by depression of gonadal function and delayed puberty
o Lesions that lead to the loss of pineal cells are associated with precocious puberty
o Pineal secretory products exert an inhibitory influence on gonadal formation |
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Term
| • Vasculature of The Diencephalon |
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Definition
o The anterior choroidal artery originated from the cerebral portion of the internal carotid artery and courses caudolaterally along the trajectory of the optic tract
o It sends penetrating branches into the genu of the internal capsule and into the more inferior aspect of the posterior limb of the internal capsule
o It serves the optic tract, inferior portions of the lenticular nucleus, the ch0roid plexus of the inferior horn of the lateral ventricle, and large parts of the hippocampal formation
o An occlusion of this artery leads to choroidal artery syndrome resulting in characteristic visual and motor deficits that reflect damage to the optic tract and the inferior portion of the posterior limb of the internal capsule
o Although the thalamus receives a blood supply largely separate from that of the internal capsule, vascular lesions in the thalamus may extend into the internal capsule or vice versa
o Ischemic or hemorrhagic strokes in the hemisphere may result in contralateral hemiparesis in combination with hemianesthesia; these losses correlate with damage to corticospinal and thalamocortical fibers in the internal capsule
o Strokes involving the larger thalamic arteries, such as the thalamogeniculate artery, may result in total or dissociated sensory losses
o These patients may subsequently experience persistent, intense pain (thalamic pain, Dejerine-Roussy syndrome) |
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Term
| o Posterior column deficits |
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Definition
| may be seen in cases of trauma or vascular compromise |
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Term
| o Lesions of the posterior column-medial lemniscus system caudal to the sensory decussation |
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Definition
| decussation result in ipsilateral sensory deficits; lesions rostral to this decussation result in contralateral deficits (pg 269-270) |
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Term
| o Bilateral compromise of the posterior columns in the spinal cord |
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Definition
| result in a loss of discriminative touch, vibratory sense, and position sense bilaterally below the level of the lesion |
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Term
| o Damage to the sensory trigeminal root, or the principal sensory nucleus |
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Definition
| may result in a loss of tactile discrimination, proprioception, and kinesthesia from the head |
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Term
| • Slowly Adapting Peripheral Mechanoreceptors |
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Definition
o Merkel cells, Ruffini corpuscles, and some hair follicle receptors signal tonic evens such as discrete small indentations in the skin
o They provide input related to both the displacement and velocity of a stimulus
o They are capable of encoding stimulus intensity of duration because they are slowly adapting (SA) and are active so long as the stimulus is present
o For example, Merkel cell complexes are crucial to reading Braille |
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Term
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Definition
presents symptoms indicative of damage to fibers of the posterior columns in the spinal cord
o This disease is caused by infection with Treponema pallidum and is associated with neurosyphilis
o The fibers of the posterior columns degenerate, and the patient has ataxia(related to the lack of sensory input), a loss of muscle stretch(tendon) reflexes, and proprioceptive losses from the extremities |
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Term
| • Primary Somatosensory Cortex |
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Definition
o Small lesions in various parts of the primary somatosensory cortex (S1) may result in characteristic types of sensory losses
o Lesions involving area 1 produce a deficit in texture discrimination
o Damage to area 2 results in loss of size and shape discrimination (astereognosis)
o Injury to area 3b has a more profound effect than that from damage to either area 1 or 2 alone, producing deficits in both texture and size and shape discrimination
o This difference suggest that there is hierarchical processing of tactile information in S1 cortex, with area 3b performing the initial processing and distributing he information to area 1 and 2
o Lesions involving the somatosensory cortex usually include larger areas and frequently result in more global deficits, such as a loss of proprioception, position sense, vibratory sense, and pin and thermal sensations on the contralateral side of the body |
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Term
| • Additional Cortical Somatosensory Cortex |
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Definition
o The secondary somatosensory cortex (S2) lies deep in the inner face of the upper bank of the lateral sulcus; it contains a somatotopically organized representation of the body surface
o Inputs to S2 cortex arise from the ipsilateral S1 cortex, as well as from the ventral posterior inferior nucleus
o This cortical area is supplied primarily by the middle cerebral artery
o Posterior to area 2, additional parietal cortical regions also receive tactile inputs; these regions include area 5 and lateral portions of area 7 (7b)
o Lesions in the parietal association area can produce agnosia, in which contralateral body parts are lost from the personal body map
o Sensation is not radically altered, but the limb is not dressed and is not recognized as part of the patient’s own body |
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Term
| • Plasticity and Reorganization in the Primary Somatosensory Cortex |
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Definition
o Some individuals appear to “recover” lost functions, whereas others remain relatively unchanged after brain injury
o In general, the younger the person suffering the injury, the more “recovery” is noted
o The brain of a child is quite malleable or plastic; it forms multiple, redundant neural connections linking various brain areas
o Many of these connections will be retained, through usage and experience, whereas others will be “pruned” by programmed cell death (apoptosis) and other cellular mechanisms
o These processes will continue for a finite period of time (critical period), thus giving many brain regions the potential to function in a variety of ways
o Children suffering brain trauma due to a birth injury may appear to be quite normal with respect to sensory, motor, and cognitive abilities; only after inspection of a brain scan that the abnormal brain anatomy resulting from the injury is appreciated
o The developing brain possesses the ability to reassign brain functions to other brain regions; this is commonly referred to as plasticity
o In contrast to that in children, the nervous system in the adult has passed beyond the critical periods of brain development and has become relatively nonmalleable
o However, somatosensory cortex can undergo reorganization e.g. changes in cortical map following limb or digit amputation which one study has shown to be quite rapid
o A similar mechanism is also probably at work in older patients who suffer a stroke; in these patients there may initially be a complete loss, followed by a partial recovery that may extend over many months
o In contrast to younger patients, who may experience a complete (or almost complete) recovery, older patients may experience less than full recovery; the older the brain, the less plasticity it seems to have |
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Term
| o Pain, thermal, and nondiscriminative touch sensations |
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Definition
| transmitted via a composite bundle called anterolateral system |
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Term
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Definition
o Nociceptors (pain receptors) are found in cutaneous as well as in deep structures
o Two major classes of cutaneous pain receptors have been identified Aδ (A-delta) mechanical nociceptors and C-polymodal nociceptors
o These receptors are found at the end of the peripheral processes of thinly myelinated (Aδ) or nonmyelinated (C) fibers
o The cutaneous receptive field of an Aδ nociceptor consists of a number of small sensitive spots (2 to 30) scattered over an area of skin; each spot ranges from 50 μm to 180 μm in diameter and respond to mechanical injury accompanied by tissue damage
o Aδ fibers carry well-localized sensations, which do not evoke an affective component to the sensory experience; a pinprick, used clinically to test ALS function, is one stimulus that activates Aδ fibers
o C-polymodal nociceptors respond to mechanical, thermal, and chemical stimuli; the cutaneous receptive field of a C-polymodal nociceptor usually consists of one to two sensitive spots, with each spot covering an area of skin of 1 mm2 to 2 mm2
o C fibers transmit poorly localized sensations that produce a noticeable affective component e.g. a dull, persistent ache that follows a muscle pull
o C fibers spots are larger but fewer in number than the Aδ spots, which are smaller but more numerous
o Local anesthetics, such as lidocaine or bupivacaine, preferentially affect small-diameter Aδ and C fibers and thus result in loss of nociception (analgesia) |
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Term
| • Peripheral Sensitization and Primary Hyperalgesia |
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Definition
o Pain receptors, unlike Meissner corpuscles or Merkel cells, demonstrate a unique phenomenon called sensitization
o Following an insult, these receptors become more sensitive (lower pain threshold) and thus more responsive (increases in firing rate) to noxious stimulation within their receptive fields
o Chemicals released by the damaged skin or byproducts from plasma, or both, are thought to contribute to sensitization
o As a result of this heightened sensitivity, the affected area is exquisitely sensitive to painful stimuli and patients experience a sensory disturbance called hyperalgesia (exaggerated response to a painful stimuli)
o This condition can be differentiated primary hyperalgesia and secondary hyperalgesia
o Primary hyperalgesia occurs in the region of damaged skin and is probably the result of receptor sensitization |
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Term
| • Central Sensitization and Secondary Hyperalgesia |
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Definition
o Secondary hyperalgesia occurs in the skin bordering the damaged tissue
o Although receptor sensitization may contribute to secondary hyperalgesia, there is likely to be a central (e.g. spinal) component as well
o Sensitization of peripheral nociceptors causes an increase in spontaneous activity in the Aδ and C fibers
o The central processes of these fibers enter the posterior horn of the spinal cord, where they activate posterior horn neurons
o Ongoing inputs from these injured peripheral nociceptors evoke a number of changes in the central processing of sensory information by the posterior horn neurons
o These changes include a marked increase in the receptive field size of the posterior horn neuron (to include skin areas not involved in the initial injury), an increased response of the cells to the application of suprathreshold stimuli, a decreased threshold to stimulus application in the receptive field, and activation of the cell by novel inputs (e.g. a light breeze)
o This phenomenon is known as central sensitization, and it represents a potentiated state in which the system has been shifted from one function level (normal) to another (sensitized) by a change in transcription
o In some patients, an innocuous stimulus, such as a gentle breeze or a light touch, can evoke pain sensation in the skin bordering the damaged tissue; the perception of an innocuous stimulus as painful is referred to as allodynia and can be the result of central sensitization |
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Term
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Definition
o Visceral pain is often described as being diffuse and difficult to localize and is frequently referred to an overlying somatic body location and usually involves autonomic reflexes
o Visceral pain receptors located in the heart, respiratory structures, the gastrointestinal tract, and the urogenital tract are poorly identified
o These receptors can be activated by intense mechanical stimuli including overdistention or traction, ischemia, and endogenous compounds, including bradykinin, prostaglandins, H+ ions, and K+ ions; activation of these receptors produces pain |
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Term
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Definition
is a procedure in which posterior roots are sectioned in an attempt to alleviate intractable pain
o In addition to their normal trajectory (lateral division) into the posterior horn, a small number of C fibers enter the spinal cord through the anterior root of the spinal nerve; it is possible that these fibers provide a basis for the return of pain after posterior rhizotomy |
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Term
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Definition
o Shingles (herpes zoster) is a disease of viral etiology that is noteworthy for its dermatomal distribution
o Subsequent to a bout of chickenpox, viral DNA may infect and become latent in trigeminal and posterior root ganglion cells
o The virus may reactivate periodically, producing infectious virions that travel down the peripheral processes of the neurons to produce a painful skin irritation in the dermatomal distribution of the ganglion
o When an injury or disease process affects a series of nerve roots, the result is diminished sensibility (hypesthesia) over the dermatomes served by these roots
o The borders of the hypethetic region correspond to dermatomal boundaries
o The most debilitating aspect of this disease is a poorly understood recurrence of pain
o Known as postherpetic neuralgia, this condition is a neuropathic pain |
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Term
| • Clinical Tests For ALS and PCML Systems |
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Definition
o Clinically, it is important to test patients for intact ALS and PCML systems function
o In testing the ALS, a single pin point applied to the skin should evoke a response (perception of pain) from the patient
o Function of the intact PCML system is tested by the simultaneous application of two points spaced at measured intervals; as the points are moved closer, the ability to identify them as separate stimuli (two-point discrimination) decreases and eventually disappears
o The PCML system is also tested by applying a 128-Hz tuning fork (vibratory sense) to a bony prominence or the tip of a finger or toe; the patient perceives this as a buzzing sensation
o It is common to test both the pain/thermal sense and discriminative touch/vibratory sense on both sides of the face and body to see if there are asymmetries |
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Term
| • Direct and Indirect Spinothalamic Pathways |
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Definition
o The fibers of the ALS participate in both direct and indirect spinothalamic pathways
o Most Aδ fibers participate in the direct (neospinothalamic) pathway, which carries nondiscriminative tactile, innocuous thermal, and nociceptive signals
When these Aδ fibers enter the posterolateral fasciculus and bifurcate, their branches travel rostrocaudally for three to five spinal levels
The descending branches terminate on interneurons within the spinal gray that participate in segmental spinal reflexes
The ascending branches terminate on second-order neurons (tract cells) in lamina I of the posterior horn; these tracts cells, in turn, project to the thalamus
The great majority of their axons cross the midline of the spinal cord obliquely via the anterior white commissure and ascend in the contralateral ALS; a few ascend in the ipsilateral ALS
The thalamic (third-order) neurons of these pathways are located mainly in the VPL, the posterior nucleus, and the intralaminar nuclei
o The polysynaptic indirect (paleospinothalamic) component of the ALS, which originates chiefly from C fibers, relays noxious and innocuous mechanical and thermal information to the brainstem reticular formation
Branches of these fibers ascend and descend by one or two levels in the posterolateral fasciculus to synapse on interneurons in laminae II and III
These interneurons influence tract cells in laminae V to VIII, which send axons that cross obliquely through the anterior white commissure (over a distance of one to three segments) to join the contralateral ALS
These spinoreticular fibers terminate in the brainstem reticular formation, which in turn projects to the thalamus |
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Term
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Definition
o Brown-Sequard syndrome is a hemisection of the spinal cord which results in a combination of sensory and motor losses
o Sensory deficits include:
1) Contralateral loss of nociceptive and thermal sensations over the body below the level of the lesion (ALS damage)
2) Ipsilateral loss of discriminative tactile, vibratory, and position sense over the body below the level of the lesion (posterior column damage)
o The motor loss is manifested as an ipsilateral paralysis of the leg or leg and arm, depending on the level of the hemisection |
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Term
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Definition
o A condition in which there is cystic cavitation of central regions of the spinal gray matter, may impinge on the anterior white commissure and decussating ALS fibers
o When located at the C4 to C5 levels of the spinal cord, this lesion produces bilateral loss of nondiscriminative tactile, nociceptive, and thermal sensations beginning several segments below the level where the fibers are interrupted
o The symptoms present as sensory losses in the configuration of a cape draped over the shoulders and extending down to the nipple level |
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Term
| • Dissociated Sensory Loss |
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Definition
o Vascular lesions or tumors in the lower brainstem can affect discriminative touch and nociception differentially e.g. a lesion in medial portions of the medulla may result in a contralateral loss of discriminative touch and vibratory sense but not of pain and thermal sensation
o This is a dissociated sensory loss (one modality absent but not another) |
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Term
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Definition
o Injury to trigeminal nerve fibers produces a paresthesia restricted to specific regions of the face
o Tic douloureux (trigeminal neuralgia) produces episodic “paroxysmal” pain usually restricted to the peripheral distribution of the maxillary or mandibular division on one side
o Trigeminal neuralgia is further characterized by the presence of “trigger zones,” which, upon the most gentle stimulation (such as a light breeze or a brush with a wisp of cotton), produce stabbing pain on one side of the face
o The precise etiology of this condition remains enigmatic, but vascular compression of the trigeminal nerve root and the presence of microneuromas are likely causes |
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Term
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Definition
o Vascular lesions involving the posterior inferior cerebellar artery produce characteristic sensory symptoms collectively known as lateral medullary (Wallenberg) syndrome or posterior inferior cerebellar artery syndrome
o The sensory symptoms of this syndrome may include a contralateral loss of pain (hemianalgesia) and temperature (hemithermoanesthesia) sensibility over the body and ipsilateral loss of these modalitites over the face
o The extent of damage following posterior inferior cerebellar artery lesions shows remarkable variation, and the combination of symptoms is representative of the structures served by this artery |
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Term
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Definition
o Single-neuron recording and microstimulation have demonstrated that neurons within the human VPM/VPL (collectively called ventrocaudal [Vc] nuclei by some neurosurgeons) are involved with processing of tactile, thermal, and pain signals
o Patients report that microstimulation of Vc evokes sensations of touch, warmth, coolness, tingling, burning, or pain localized to specific body areas
o These recordings also reveal that a population of thalamic cells activated by innocuous tactile stimuli are mixed with other neurons activated by mechanical and thermal stimuli in painful range
o Single-neuron recording has demonstrated that microstimulation in the Vc evokes the sensation of angina, suggesting that these nuclei play a role in pain localization regardless of its origin, that is, cutaneous or visceral
o The human Vc nuclei can undergo changes (i.e. exhibits plasticity) following deafferentation, which can occur directly as a result of damage to ascending pathway s or secondarily as a result of removing sensory inputs (e.g. amputations)
o These changes may contribute to chronic pain or phantom limb pain; they involve the upregulation and downregulation of neurochemicals within the nucleus, changes in local circuitry, and changes in the functional state of Vc neurons
o For example, in patients who have undergone leg amputation, single-neuron recordings reveal that the thalamic region formerly receiving input form the lower leg and foot responded to stimulation of the stump (thigh); these patients also described the presence of nonpainful tingling over the stump in response to microstimulation in this same area |
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Term
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Definition
o Lesions have been centered in either the lateral thalamus or the medial thalamus
o Lateral thalamic lesions involve the somatosensory thalamus (VPL/VPM); although producing some transient relief for pain, these lesions produce unwanted side effects, including loss of cutaneous and position sense in the affected limb, as well as impaired motor functions
o Lesions in the medial thalamus involve the centromedian-parafascicular (CM-PF) complex as well as the central lateral nucleus (CL) and the medial dorsal nucleus; medial thalamic lesions produce transient relief from intractable pain but fail to produce loss of pain and thermal sensations; these do not produce the unwanted sensory loss seen with lateral thalamic lesions |
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Term
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Definition
o Deep brain electrical stimulation has been used for more than several decades in patients suffering form chronic pain or deafferentation pain
o Stimulating electrodes centered in the somatosensory thalamus, the CM-PF complex, or the periventricular gray (PVG)-PAG activate neurons within their vicinity and thus may contribute to stimulus-induced analgesia
o Cortical stimulation has also been shown to produce relief of chronic pain of neuropathic origin
o An evaluation of different brain regions that may contribute to the stimulus-induced analgesia was carried out using PET
o Following thalamic stimulation, increased regional cortical blood flow was noted in the rostral insula, a region activated in studies of experimental pain, neuropathic pain, and warm and cool innocuous stimuli, as well as in the anterior insular cortex
o These results suggest that stimulation of the somatosensory thalamus may activate a pain modulation circuit that involves thalamocortical thermal pathways |
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Term
| • Central or Thalamic Pain |
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Definition
o Central or thalamic pain is poorly understood sequela of natural or surgical lesions of structures involved in somatic sensibility
o Central pin was originally observed with thalamic lesions, but it can occur with lesions of the ALS below the level of the thalamus
o Central pain syndrome can also result from vascular lesions e.g. patients surviving the Wallenberg syndrome may ultimately develop central pain, suggesting some sparing of alternate or parallel pain pathways
o In central pain syndrome, the analgesia that initially results from the lesion is replaced after a period of weeks, months, or years by spontaneous paresthesia (burning, prickling, tingling), dysesthesia (impaired, disagreeable, or abnormal sensations), or unusual painful responses
o Allodynia, pain resulting from a stimulus that does not normally evoke pain, and hyperalgesia, an increased response to a stimulus that is normally painful, are common neurologic signs associated with the central pain syndrome
o Patients often characterize central pain as burning, aching, prickling, or lacerating and as occurring in paroxysms that vary in intensity and are poorly localized
o Central pain may last for years and is intractable to current analgesics
o Pharmacologic agents, such as antidepressants and antiepileptic drugs, have been used with varying degrees of success to treat central pain
o Although the etiology for this condition has not been elucidated, it is possible that this type of pain represents a deafferentation phenomenon, that is, it results from removal of primary afferent influence eon central neurons
o The time course and symptoms of central pain suggest that it may be due to the sprouting of inappropriate connections of non-nociceptive or nociceptive fibers, to increased excitability of central pain neurons, or to removal of inhibitory influences on pain neurons
o Patients experiencing central pain may obtain temporary relief from transcutaneous electrical nerve stimulation (TENS) (electrical stimulation of nerves through the skin), from electrical stimulation of the posterior columns, or from chronic stimulation of the PAG or PVG regions by stereotaxically positioned electrodes (deep brain stimulation)
o Neuroablative surgical procedures that have been used in the treatment of central pain include anterolateral cordotomy, trigeminal tractotomy, lesions of the posterior root entry zone, thalamotomies, and cortical ablation
o None of these procedures are successful in the long term |
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Term
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Definition
o Stimulation-produced analgesia (SPA) relies on electrical stimulation of CNS structures to induce the release of endogenous chemicals, such as enkephalin, from cells in pain control circuits; endogenous opiates such as enkephalin inhibit pain transmission
o Stimulation of PVG, the PAG, or the nucleus raphe magnus results in the release of enkephalin or monoamines producing analgesia
o Systemic administration of pharmacologic opiates, such as morphine, excites periventricular and periaqueductal neurons, supplementing their natural activity
o This increase in activity suppresses neurons in the spinal and medullary posterior horns that transmit painful information, also producing analgesia
o The direct delivery of opioids to the spinal cord (epidural anesthetic techniques) also is used to produce a powerful analgesia for surgical procedures and deliveries
o Current therapies for control of pain transmission include transcutaneous electrical nerve stimulation and chronic stimulation of the posterior columns by implanted electrodes
o Posterior column stimulation activates large-diameter myelinated fibers; antidromic activation of these fibers discharges collaterals in the posterior horn; these collaterals stimulate the enkephalinergic interneurons in the posterior horn that inhibit the transmission of pain signals
o This stimulation also provides long-term diminution of pain for reasons that are poorly understood
o Acupuncture-like stimulation also may produce local analgesia by stimulating these fibers |
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Term
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Definition
Free nerve endings of Aδ and C fibers located in the heart, respiratory structures, gastrointestinal tract, and urogenital tract
Respond to stimuli that have the potential to damage tissue or to stimuli resulting from the presence of damaged tissue e.g. intense mechanical stimuli (overdistention or traction), ischemia, and endogenous compounds (bradykinin, prostaglandins, and H+ and K+ ions)
Receptors signal changes in visceral structures that result from pathologic process such as myocardial ischemia or appendicitis or from benign conditions such as gastrointestinal cramping or bloating
Visceral pain is often described as being diffuse or referred and difficult to localize |
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Term
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Definition
Responsive to innocuous stimuli and monitor the functions of visceral structures on a continuing bases
Mediate normal visceral reflexes such as baroreceptor reflex
Examples of physiologic receptors are:
1) Rapidly adapting mechanoreceptors signal occurrence of dynamic events such as movement or sudden changes in pressures e.g. free nerve endings that exist in the epithelia of pulmonary airways that are sensitive to the presence of inhaled particles are also known as “cough receptors”; largest example is the pacinian corpuscle
2) Slowly adapting mechanoreceptors signal the presence of stretch or tension within a visceral structure; essential for the perception of fullness in organs such as stomach and bladder
3) Specialized receptors includes (1)baroreceptors respond to rapid increase in arterial blood pressure, (2)chemoreceptors responds to acidity and oxygen and carbon dioxide tension in arterial blood, (3)osmoreceptors responds to osmolarity of extracellular fluid, and (4)internal thermal receptors
4) Specialized receptors also exists in the hypothalamus as chemoreceptors, osmoreceptors, and internal thermal receptors and are activated by changes in blood chemistry or osmolarity or by changes in temperature of blood circulating through the hypothalamus |
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Term
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Definition
o Visceral efferents (GVE) fibers travel through the sympathetic nerves such as the splanchnic and cardiac nerves or through parasympathetic nerves such as the vagus and pelvic nerves
o These sympathetic and parasympathetic nerves also contain viscerosensory (general visceral afferent [GVA]) fibers
o Visceral afferents fibers tend to predominate in the parasympathetic nerves but are comparatively sparse in the sympathetic nerves e.g. more than 80% of the fibers in the vagus nerve are viscerosensory whereas less than 20% of fibers in the greater splanchnic nerve are visceral afferents
o Most visceral afferents (90%; both sympathetic and parasympathetic) are either unmyelinated or thinly myelinated and, therefore, are slowly conducting fibers
o Information originating from nociceptors (visceral pain) is conducted almost exclusively by sympathetic nerves
o Input originating from physiologic receptors (innocuous input) travels primarily in parasympathetic nerves |
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Term
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Definition
o A phenomenon whereby noxious stimuli that originate in a visceral structure, such as the heart or the stomach, are perceived by the patient as pain arising from a somatic portion of the body wall such as the skin, bones, or skeletal muscles
o Certain patterns of referred pain are clearly diagnostic of disease in particular visceral locations e.g. pain in the chest (sometimes perceived as intense pressure) that radiates down the left arm may be indicative of a serious heart problem |
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Term
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Definition
o Referred pain is frequently associated with diseases of the heart
o Frequently called angina pectoris because it is perceived as a pain of the chest, including the sternum and pectoral muscles
o In 80% of patients, angina is initially perceived as an unpleasant squeezing sensation originating from behind the sternum
o Discomfort may also be perceived as pain radiating down the left arm or, more rarely, down both arms
o On rare occasions, the pain has been reported to radiate bilaterally into the neck, jaw, and temporomandibular joints
o Predilection of the pain for the left side of the chest or extending down the left arm, reflects the predominance of myocardial disease in the left side of the heart |
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Term
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Definition
o Hypertension is abnormally elevated blood pressure; it is a major health issue and has a variety of causes
o Hypotension is abnormally low blood pressure |
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Term
| • Reticular Activating System |
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Definition
o Axons from the reticular formation of the brainstem to the cerebral cortex with the largest number terminating in the frontal lobe are called reticulothalamic and thalamocortical pathways; these pathways “alert” or “activate” the cerebral cortex
o The reticular formation receives viscerosensory input via spinoreticular fibers and collaterals from the ALS
o Some of these ascending fibers to the reticular formation convey nociceptive visceral afferent information originating from the gut on sympathetic afferent fibers
o Other ascending fibers convey a sense of bladder (or bowel) fullness originating from the pelvic viscera on parasympathetic afferents
o Both types of viscerosensory input feed into the reticular formation and participate in the “arousal” of the cerebral cortex through the ascending reticular activating system (ARAS) e.g. either sudden pain from the stomach or small intestine or the stimulus of a full bladder will excite the reticulothalamocortical circuit and wake a person from a deep sleep
Initial sensation is not one of specific information (full bladder, stomach pain) but rather the sense of just being awakened; once cortex has been “alerted,” conscious/perceptive part of the brain takes over |
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Term
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Definition
o Congenital megacolon, or Hirschsprung disease, results from a failure of these enteric neuronal precursor cells to migrate into the wall of the developing lower gut
o As a result, the affected segment of the gut (the portion lacking enteric ganglion cells, the aganglionic segment), usually the colon, is paralyzed in a constricted state, with consequent distention of the proximal, and normally innervated (the portion containing enteric ganglion cells, the ganglionic segment), portion of the intestine
o Most commonly seen in the very young (newborn to 6 years) but may be seen in adults
o Although the presentation of the disease is strikingly characteristic on a radiograph or with MRI, definitive diagnosis relies on biopsy and histologic confirmation of a lack of enteric ganglion neurons in the affected segment
o The treatment of choice is to resect the aganglionic segment and join the remaining normal portions of the gut |
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Term
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Definition
o Development of the autonomic nervous system requires an elaborate sequence of intercellular signaling that involves two major families of neurotrophic factors
o One is the glial cell line-derived neurotrophic factor (GDNF) family, which consists of several distinct signaling molecules and their receptors
Mutations of one of these receptors, designated RET, is the underlying cause of some cases of congenital megacolon
o The neurotrophins are the other large family of neurotrophic factors
As with the GDNF family, each neurotrophin regulates development and function of specific populations of PNS and CNS neurons via binding to specific receptors
The existence of these neuronal growth factors was first demonstrated when the neurotrophin growth factor (NGF) was discovered as a target-derived messenger molecule that is absolutely essential for survival and development of sympathetic postganglionic neurons as well as those primary sensory neurons that are involved in pain
The pathologic changes in animals deprived of NGF or its high affinity receptor are similar to those seen in patients with congenital insensitivity to pain and with anhidrosis (hereditary sensory and autonomic neuropathy type IV), an autosomal recessive disease |
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Term
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Definition
o The largest of the paravertebral (sympathetic chain) ganglia is the superior cervical ganglion
o Postganglionic fibers from these cells innervate blood vessels and cutaneous targets of the face and scalp and the neck of the territories supplied by the first four cervical nerves
o The superior cervical ganglion also innervates the salivary glands, nasal glands, lacrimal gland, and structures of the eye such as the papillary dilator muscle and the superior and inferior tarsal muscles
o A constellation of signs and symptoms results from interruption (central or peripheral) of the sympathetic pathway through the superior cervical ganglion; these include:
1) Constriction of the pupil (miosis) caused by the unopposed action of the parasympathetically innervated papillary constrictor
2) Drooping of the upper eyelid (ptosis) resulting from paralysis of the superior tarsal muscle (of Muller)
3) Flushing of the face from loss of sympathetically mediated vascular tone
4) Diminished for absent sweating (anhidrosis) on the face |
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Term
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Definition
o In special circumstances, sympathetic activation can become linked to pain
o Causalgia (complex regional pain syndrome type II) is a syndrome that can result from partial injury to a peripheral nerve, typically a nerve serving an extremity
o Signs and symptoms include:
1) Spontaneous burning pain
2) Hypersensitivity of skin
3) Pain triggered by loud noises or strong emotions
4) Sweating and reduced temperature of the limb
5) Mottling of skin
6) Swelling of the extremity
o A striking feature of causalgia is that symptoms can often be alleviated by sympathectomy or otherwise blocking sympathetic function
o Prevailing theory of the etiology of the pain associated with the syndrome is that sympathetic postganglionic neurons coursing in the injured nerve develop abnormal connections to nociceptive dorsal root ganglion neurons
o This pathologic process could occur either in the tangle of regenerated nerve fibers that form a neuroma or within the sensory ganglion
o The nociceptive neurons may develop abnormal responsiveness to adrenergic stimulation |
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Term
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Definition
o CNS influence over activities of the digestive system is conveyed by sympathetic and parasympathetic pathways but the digestive tract is able to perform its basic functions with a remarkable degree of independence from regulation by the CNS
o This high degree of autonomy of digestive functions is possible because the wall of the gut (esophagus to anus) is equipped with an elaborate intrinsic network of neurons termed the enteric nervous system or intrinsic nervous system of the gut
o The enteric nervous system is regarded by some authorities as the third divion (along with the sympathetic and parasympathetic divisions) of the autonomic nervous system
o It has been estimated to comprise roughly 100 million neurons, approximately the same number found in the spinal cord
o The majority of enteric neurons are distributed within the myenteric and submucosal plexuses, although there are additional plexuses in the mucosa and serosa
o Over a dozen distinct functional types of intrinsic neurons have been identified including several kinds of sensory neurons (mechanoreceptors, chemoreceptors, nociceptors), interneurons (excitatory, inhibitory, orally projecting, caudally projecting), and motor neurons (secretomotor, excitatory and inhibitory muscle motor)
o Smooth muscle-like cells called interstitial cells of Cajal (ICC) spontaneously initiate rhythmic electrical activity like the pacemaker cells of the heart; input from the enteric nervous system is necessary to translate the slow waves of depolarization into useful waves of contractions
o A prominent specific function of the enteric nervous system is the peristaltic reflex whereby the presence of ingested material in the intestine evokes waves of contraction and relaxation that slowly propel the material toward the anus
o Although the peristaltic reflex and other basic reflexes can occur independently of external signaling they are normally subject to extrinsic regulation by parasympathetic input (generally enhancement) and sympathetic input (generally inhibitory)
o An extremely diverse array of neurotransmitters and neuromodulators are involved in the functions of the enteric nervous system such as small molecules (acetylcholine, norepinephrine, ATP, serotonin), a gas (NO), and numerous polypeptides (substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, cholecystokinin, dynorphin, enkephalins, neuropeptide Y)
o Some chemical messengers such as 5HT can either be excitatory or inhibitory depending on the receptor
o Various molecular signaling systems provide important targets of pharmacologic therapies for disorders of gut motility e.g. agonists and antagonists that target specific subtypes of neurotransmitter receptors are used to treat irritable bowel syndrome |
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Term
| • Major Central Nervous System Components |
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Definition
o The importance of the supraspinal control of autonomic function is illustrated by some of the deficits associated with spinal cord injuries at higher levels (T6 or above)
o Initially, the interruption of descending reticulospinal and hypothalamospinal fibers that regulate sympathetic preganglionic neurons in the intermediolateral cell column is manifested as an overall reduction in sympathetic activity
o Thus, clinical signs include lowered blood pressure, orthostatic hypotension (severe drop in blood pressure), and reduced heart rate (bradycardia)
o With time, hyperactivity of sympathetic reflexes (termed autonomic dysreflexia) develops, probably as a result of denervation hypersensitivity of sympathetic neurons and target tissues
o Signs and symptoms include hypertension, urinary retention, piloerection, profuse sweating, and reduction of blood flow to peripheral tissues in response to any of a wide variety of noxious stimuli below the level of spinal cord injury |
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Term
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Definition
o The function of the cardiovascular system is influence by mental activity, emotional state, posture, muscular exertion, visceral activity, body temperature, and concentration of blood gases and electrolytes
o In addition to mechanisms that regulate blood pressure, there is precise neural control of blood flow to specific organs and regions of the body
o The baroreceptor reflex functions to buffer blood pressure against a sudden change in posture; failure of this reflex results in orthostatic hypotension when the patient assumes an upright position
When a reclining individual stands upright, reduction in baroreceptor discharge results in decrease signals from the solitary nucleus to the vagal preganglionic parasympathetic neurons and vasopressor neurons in the rostral ventrolateral medulla to increase cardiac output, heart rate, and vascular pressure
o The chemoreceptor reflex maintains homeostasis of blood gas composition by adjusting respiration, cardiac output, and peripheral blood flow
The cardiovascular component of the chemoreceptor reflex is closely coordinated with respiration, a somatic motor function coordinated by other neurons of the brainstem reticular formation
The chemoreceptor reflex is sensitive to oxygen and carbon dioxide in the blood
o The vasopressor response increases heart rate and blood pressure; the vasodepressor response decreases heart rate and blood pressure |
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Term
| • Urinary Bladder and Micturition |
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Definition
o Emptying of the urinary bladder, micturition, is brought about by contraction of smooth muscle of the bladder wall (detrusor muscle) mediated by parasympathetic outflow and relaxation of skeletal muscle of the external urethral sphincter which is subject to both reflex and voluntary control supplied by alpha motor neurons in segments S3 to S4
o Emptying the bladder is a combination of lower motor neuron and parasympathetic activity
o The bladder wall also has a sympathetic innervations and its influence is mainly inhibitory on both the detrusor muscle and the parasympathetic postganglionic neurons in the bladder wall
o Sympathetic activity is highest during urine storage |
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Term
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Definition
o Characterized by polyuria (increased urination) and polydipsia (increased consumption of water)
o This condition is due to a deficit of circulating release of ADH from the posterior pituitary
o Lesions of the supraoptic or paraventricular nucleus or of the supraopticohypophyseal tract produces diabetes insipidus
o The pituitary is well protected in the sella turcica but it is subject to a variety of potential insults (tumor, vascular, surgical) in this confined location
The extension of the hypophyseal stalk and infundibulum through the diaphragma sella is a vulnerable relationship
Trauma to the head may result in a shearing of the stalk and the eventual development of diabetes insipidus |
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Term
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Definition
o The lateral hypothalamic nucleus is commonly referred to as the “feeding center” and lesions of this nucleus will result in attenuated feeding and will produce weight loss
o The ventromedial nucleus is generally thought of as a “satiety center” and lesions to this nucleus will result in excessive eating and weight gain |
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Term
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Definition
o The mammillary region contains four nuclei:
1) Medial mammillary nuclei
2) Intermediate mammillary nuclei
3) Lateral mammillary nuclei
4) Posterior mammillary nuclei
o Lesions of the mammillary bodies tend to impede the retention of newly acquired memory, so that an immediate memory or a short-term memory is not processed into long-term memory
o A patient with a mammillary lesion has no difficulty in remembering events occurring months or years prior to the lesion but memory for events occurring after the lesion is limited to short term (period of minutes)
o Anterograde amnesia typically results in severe difficulties learning new tasks and transforming experiences into long-term memory
o These specific memory deficits are characteristic of the Korsakoff syndrome
Condition that is caused by thiamine deficiency and is typically associated with chronic alcoholism
The memory deficits in this syndrome are caused by progressive degeneration in the mammillary bodies and in functionally related brain structures, such as hippocampal complex and the dorsomedial thalamic nucleus
Patients may have difficulty understanding written material and in conducting meaningful conversations because they tend to forget what was just read or said
Patients tend to confabulate which is stringing together fragmentary memories from various events into a synthesized memory of an “event” that never occurred |
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Term
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Definition
o Hypothalamomedullary and hypothalamospinal fibers form an essential and direct link between the hypothalamus and autonomic nuclei of the medulla and spinal cord
o Lesions in the anterolateral medulla may disrupt these fibers
o Although the effect of disrupting hypothalamomedullary fibers is not well understood, injury to hypothalamospinal fibers results in a loss of sympathetic outflow to the ipsilateral face and head causing Horner syndrome and to the ipsilateral side of the body |
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Term
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Definition
o Tumors (adenomas) occurring within the pituitary can easily encroach on the neighboring hypothalamus
o Visual deficits are frequently experience by patient with pituitary tumors e.g. a pituitary tumor pressing on the optic chiasm may damage axons originating from the nasal half of each retina; this may result in a loss of vision in the temporal half of the visual field for each eye (a bitemporal hemianopia) reducing peripheral vision
o Tumors occurring within the pituitary gland account for 12% of primary brain tumors
o These tumors occur most frequently in young adults and are generally noncancerous
o Incidental adenomas occur with increasing frequency in the 5th, 6th, and 7th decade of life
o Pituitary tumors can be classified according to their secretory characteristics, size, or biologic invasiveness
o Microadenomas are tumors less than 1 cm, whereas tumors greater than 1 cm are referred to as macroadenomas
o Invasiveness tumors may erode and extend into the dura mater and even the sphenoid bone
o Nonsecreting pituitary tumors do not secrete hormones and as a result are often undiagnosed until they grow to a considerable size and exert pressure on nearby structures
o Patients with large pituitary tumors have symptoms that often include visual disturbances (60% to 70%) and headaches
o Secreting Tumors
Commonly referred to as hormonally active tumors or hypersecreting tumors
The clinical manifestations of a secreting tumor are the effects of the biologic activity of the specific pituitary hormone that is overproduced |
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Term
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Definition
o Excessive production of growth hormone leads to uncontrolled growth in height (gigantism), if the growth occurs before closure of the epiphyseal plates
These patients may have large muscles, but they are weak because these muscles contain excessive amounts of connective tissue rather than muscle fibers
o Overproduction of growth hormone after the growth plates have closed results in a condition termed acromegaly, referring to the enlargement of the digits of the patient
Patients with acromegaly typically have
1) Facial changes with elongation of the face
2) Malocclusion of the jaw
3) Gaps in the lower dentition
4) Frontal and mastoid sinus bulges
5) Bulbous nose
6) Thickened lips
7) Very large hands and feet
8) Excessive cortical thickening of bone
9) Cardiac failure secondary to heart enlargement (cardiomegaly)
10) Hypertension
11) Diabetes mellitus |
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Term
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Definition
o Much rarer form of pituitary tumor can result from the overproduction of thyrotropin hormone
o The result may either be hypothyroidism or hyperthyroidism
o The patients frequently suffer from abnormal cardiovascular function as well as tremor
o With the progression of these tumors, symptoms such as headaches, visual disturbances, and parasellar cranial nerve (i.e. CN III, IV, and VI) dysfunction may be recognized
o The CN dysfunction generally involves the abducens nerve(s) first, then the oculomotor and trochlear nerve as the tumor enlarges in the lateral direction |
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Term
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Definition
o An overproduction of corticotropin leads to a form of hyperadrenalism known as Cushing disease
o Excessive ACTH from the pituitary gland result in excessive adrenal cortisol secretion
o Affected patients have:
1) Central truncal obesity with violaceous striae (stretch marks) which are clearly different from those seen in pregnancy or excessive weight gain (Cushing-purple to violet, pregnancy or overweight-white)
2) Moon-like facies
3) Facial hirsutism
4) Dorsal cervical hump, commonly called buffalo hump which results from enlargement of the fat pad in this area
5) Hyperpigmentation
6) Easy bruising
7) Hypertension
8) Osteopenia
9) Emotional lability |
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Term
| • Prolactin-Secreting Tumors |
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Definition
o An overproduction of prolactin in women results in the syndrome of galactorrhea (milk production) and amenorrhea (absence of menstrual periods)
o Prolactin is the most commonly affected hormones in secreting tumors
o Hyperprolactinemia is seen physiologically as part of a normal pregnancy
o Hypothyroidism and drug use could contribute to hyperprolactinemia in nonpregnancy situations
o In men, hyperprolactinemia may be indicated by decreased libido, impotency, or infertility
o This type of hypersecretory tumor is the most common pathologic cause of infertility |
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Term
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Definition
o These tumors consists of cells that produce either excessive luteinizing hormone (LH) or follicle-stimulating hormone (FSH)
o Excessive secretion of FSH causes no known symptoms in either men or postmenopausal women
o Excessive LH secretion has been reported to cause premature pubertal changes (precocious puberty) in males and possibly disruption of the ovarian cyclicity in females
o Frequently gonadotrope adenomas come to clinical attention because of their mass effect, with visual impairment, headaches, and occasionally diplopia (double vision) caused by optic nerve compression |
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Term
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Definition
o All vital functions of the hypothalamus, including the maintenance of blood pressure, body temperature, and water balance are controlled through reflexes and are typically not subject to conscious control
o Some people can learn to alter certain hypothalamic responses e.g. biofeedback training enables some people to alter blood pressure and body temperature, which are generally under hypothalamic control |
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Term
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Definition
Regulates blood pressure in response to input from baroreceptors in the aortic arch and carotid sinus
The solitary nucleus contains cells that transmit baroreceptor information to the paraventricular, dorsomedial, and lateral hypothalamic nuclei which in turn projects to the dorsal vagal nucleus in the medulla |
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Term
| o Temperature Regulation Reflex |
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Definition
Specialized temperature-sensing neurons in the hypothalamus called intrisinc receptors sense the temperature of blood
When the temperature rises above normal, these neurons stimulate regions in the rostral hypothalamus which are responsible for activating physiologic mechanism for heat dissipation-sweating and cutaneous vasodilation
When temperature is below normal, these neurons timulate regions in the caudal hypothalamus to activate mechanism for heat conservation-cutaneous vasoconstriction mediated by autonomic pathways and for heat production-shivering mediated by reticulospinal pathways |
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Term
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Definition
Unlike the baroreceptor and temperature regulation reflexes, which are entirely neural, the water balance reflex is neurohumoral; its efferent limb consists of a hormonal signal carried by ADH
The osmolarity of the blood is monitored by specialized osmolarity-sensitive neurons located in the anterior hypothalamus near the preoptic and paraventricular nuclei
The output from these receptors influences the release of ADH by neurons in the supraoptic and paraventricular nuclei
When blood osmolarity is too high, more ADH is released; when blood osmolarity is too low, less ADH is released |
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Term
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Definition
o Circuits within the brain presumably associated with emotions and/or emotional behavior were proposed by James Papez
o Initial segment of the Papez circuit is a projection primarily from the subiculum, to the medial mammillary nucleus via the postcommissural fornix
o The circuit is completed by the following connections:
1) Mammillothalamic tract connecting the medial mammillary nucleus to the anterior nucleus of the thalamas
2) Thalamocortical fibers from the anterior nucleus to broad expanses of the cortex of the cingulated gyrus
3) Projection from the cingulated cortex, via cingulum, to the entorhinal cortex and also directly to the subiculum and the hippocampus |
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Term
| • Cytoarchitectural Definitions of the Limbic Cortex |
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Definition
o Cortical regions with three to five cellular layers are called the paleocortex (paleopallium or periallocortex) and are represented by the:
1) Parahippocampal gyrus (entorhinal cortex)
2) Uncus (piriform cortex)
3) Cortex overlying the termination of the lateral olfactory stria (lateral olfactory gyrus)
o Cortical regions with only three cellular layers are classified as archicortex (archipallium or allocortex) and are represented by the dentate gyrus and hippocampus |
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Term
| • Blood Supply to the Limbic System |
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Definition
o Main vessels that serve much of the limbic system are the anterior and posterior cerebral arteries, anterior choroidal artery, and branches arising from the circle of Willis
o The subcallosal area and rostral parts of the cingulated gyrus are supplied by the branches of the anterior cerebral artery as it loops around the genu of the corpus callosum
o Most of the cingulated gyrus and its isthmus receives its blood supply via the pericallosal artery
o Temporal branches of the posterior cerebral artery supply the parahippocampal gyrus
o The uncus is primarily served by the uncal arteries, which are branches of the M1 segment of the middle cerebral artery although it may receive some small branches from the posterior cerebral artery
o The anterior choroidal artery usually originates from the internal carotid artery and follows the general trajectory of the optic tract; sends branches into the choroidal fissure of the temporal horn of the lateral ventricle; serves the choroid plexus of the temporal horn, the hippocampal formation, parts of the amygdaloid complex, tail of caudate nucleus, stria terminalis, and sublenticular and retrolenticular limbs of the internal capsule
o Vessels serving hypothalamic nuclei that are functionally associated with the limbic system originate from the circle of Willis
o Anterior nucleus of the thalamus is supplied by thalamoperforating arteries that arise from P1 segment of the posterior cerebral artery |
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Term
| • Blood Supply to the Limbic System |
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Definition
o Main vessels that serve much of the limbic system are the anterior and posterior cerebral arteries, anterior choroidal artery, and branches arising from the circle of Willis
o The subcallosal area and rostral parts of the cingulated gyrus are supplied by the branches of the anterior cerebral artery as it loops around the genu of the corpus callosum
o Most of the cingulated gyrus and its isthmus receives its blood supply via the pericallosal artery
o Temporal branches of the posterior cerebral artery supply the parahippocampal gyrus
o The uncus is primarily served by the uncal arteries, which are branches of the M1 segment of the middle cerebral artery although it may receive some small branches from the posterior cerebral artery
o The anterior choroidal artery usually originates from the internal carotid artery and follows the general trajectory of the optic tract; sends branches into the choroidal fissure of the temporal horn of the lateral ventricle; serves the choroid plexus of the temporal horn, the hippocampal formation, parts of the amygdaloid complex, tail of caudate nucleus, stria terminalis, and sublenticular and retrolenticular limbs of the internal capsule
o Vessels serving hypothalamic nuclei that are functionally associated with the limbic system originate from the circle of Willis
o Anterior nucleus of the thalamus is supplied by thalamoperforating arteries that arise from P1 segment of the posterior cerebral artery |
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Term
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Definition
o The hippocampal formation (archicortex) is composed of the subiculum, hippocampus (hippocampus proper or horn of Ammon), and the dentate gyrus
The subiculum is the transitional area between the three-layered hippocampus (archicortex or allocortex) and the five-layered entorhinal cortex (paleocortex or periallocortex) of the parahippocampal gyrus
• Dysfunctions (pg 506-509)
o Bilateral damage to the hippocampal formation may profoundly impair the ability of the patient to consolidate immediate- and short-term memory into long-term memory
First observed in 1900 by Bechterew
Immediate memory and short-term memory refer to types of memory that persist for seconds and minutes, respectively
Normally, these memories can be incorporated into long-term memory, which can be recalled days, months or years later |
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Term
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Definition
Loss of memory and cognitive function
Characterized by presence of neurofibrillary tangles, neuritic plaques, and neuronal loss in specific brain regions
Subiculum and entorhinal cortices are among the first sites in which abnormalities appear; thought to be responsible for memory deficits characteristics of Alzheimer disease |
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Term
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Definition
o The hippocampal formation (archicortex) is composed of the subiculum, hippocampus (hippocampus proper or horn of Ammon), and the dentate gyrus
The subiculum is the transitional area between the three-layered hippocampus (archicortex or allocortex) and the five-layered entorhinal cortex (paleocortex or periallocortex) of the parahippocampal gyrus
• Dysfunctions (pg 506-509)
o Bilateral damage to the hippocampal formation may profoundly impair the ability of the patient to consolidate immediate- and short-term memory into long-term memory
First observed in 1900 by Bechterew
Immediate memory and short-term memory refer to types of memory that persist for seconds and minutes, respectively
Normally, these memories can be incorporated into long-term memory, which can be recalled days, months or years later |
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Term
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Definition
o The hippocampal formation (archicortex) is composed of the subiculum, hippocampus (hippocampus proper or horn of Ammon), and the dentate gyrus
The subiculum is the transitional area between the three-layered hippocampus (archicortex or allocortex) and the five-layered entorhinal cortex (paleocortex or periallocortex) of the parahippocampal gyrus
• Dysfunctions (pg 506-509)
o Bilateral damage to the hippocampal formation may profoundly impair the ability of the patient to consolidate immediate- and short-term memory into long-term memory
First observed in 1900 by Bechterew
Immediate memory and short-term memory refer to types of memory that persist for seconds and minutes, respectively
Normally, these memories can be incorporated into long-term memory, which can be recalled days, months or years later |
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Term
| o Korsakoff Syndrome (Korsakoff psychosis) |
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Definition
Prolonged thiamine deficiency typically seen in chronic alcoholics
Thiamine deficiency causes a characteristic pattern of degeneration in the brain typically involving the mammillary bodies, some incursion into the dorsomedial nucleus of the thalamus, column of fornix, and hippocampal formation
Patients show a defect in short- and long-term memory; may appear demented and prone to confabulation → tend to string together fragments of memory from several different events to form a synthetic “memory” of an event that never occurred
Accompanied with gaze palsies and ataxia secondary to cerebellar damage, memory losses and learning difficulties, is called Wernicke-Korsakoff syndrome |
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Term
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Definition
Bilateral lesions of the anterior part of the cingulated gyrus greatly diminish emotional responses
Patient is immobile, mute, and unresponsive but not in a coma |
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Term
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Definition
Bilateral temporal lobe lesions that abolish the amygdaloid complex
Initially described in a series of animal experiments but have also been seen in patients as a result of trauma to the temporal lobe or temporal lobe surgery for epilepsy
Damage to amygdaloid complex frequently involves portions of adjacent structures and of the surrounding white matter
Damage to the amygdala and hippocampus results in a greater memory deficit than deficits noted with damage to either one alone
Patient is no longer able to recognize objects by sight (visual agnosia); may also exhibit tactile and auditory agnosia
Tendency to examine objects (even harmful objects, e.g. lit match) excessively by mouth (hyperorality) or to smell them
Compulsion to intensively explore the immediate environment (hypermetamorphosis) and overreact to visual stimuli
My no longer show fear or anger even when such actions are appropriate (placidity)
May eat in excessive amounts (hyperphagia), even when not hungry, may eat objects that are not food or inappropriate to species
Hypersexuality, takes form in suggestive behavior and talk and vague, ill-conceived attempts at sexual contact in humans
Amnesia, dementia, aphasia, depending on extent of the lesion of the temporal lobe
o Uncinate Fits (psychomotor or complex partial seizures)
Seizures that start in the area of the uncus
Aura associated with olfactory or gustatory hallucination |
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Term
| o Layer I (molecular layer) |
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Definition
Contains very few neuron cell bodies and consists primarily of axons running parallel (horizontal) to the surface of the cortex
The apical dendrites of cells located in deeper layers also ramify within layer I |
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Term
| o Layer II (external granular layer) |
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Definition
Mixture of small neurons (granule cells) and slightly larger neurons (pyramidal cells)
Their apical dendrites extend into layer I and their axons descend into, and through, the deeper cortical layers |
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Term
| o Layer III (external pyramidal layer) |
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Definition
Contains primarily small-to medium-sized pyramidal cells along with some neurons of other types
Smaller pyramidal cells are sequestered in the outer, or superficial portion while larger pyramidal cells are located in the inner, or deeper layer
Their apical dendrites ascend into the layer I and their axons descend into, and through, the deep cortical layers |
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Term
| o Layer IV (internal granular layer) |
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Definition
Consists almost exclusively of smooth (aspiny) stellate (star-like) neurons and spiny stellate neurons, both of which have sometimes been categorized as “granule cells”
Primary target for ascending sensory information from the thalamus
Free of pyramidal-shaped cells
Can be divided into outer (IVa) and inner (IVb) portions in many neocortical areas
Primary visual cortex is divided into three portions (IVa, IVb, IVc) |
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Term
| o Layer V (internal pyramidal layer) |
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Definition
Consists predominantly of medium to large pyramidal cells
Apical dendrites of medium pyramidal cells may extend upward one or two layers
Apical dendrites of large pyramidal cells extend outward to layer I
Large pyramidal cells of this layer are a major source of cortical efferent fibers including axons to the basal nuclei, brainstem, and spinal cord
Some corticocortical axons also originate in layer V; these are probably collateral branches of axons that are projecting to some subcortical target |
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Term
| o Layer VI (multiform layer) |
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Definition
Contains an assortment of neuron types including some with pyramidal and fusiform cell bodies
Dendrites of the larger cells extend into layer I while those arising from the smaller cells extend no farther than layer IV
Axons of cells of this layer project to subcortical targets, such as thalamus, and to other cortical regions as corticocortical connections
o There are prominent plexuses of horizontally running myelinated fibers in layer IV (outer band of Baillerger) and layer V (inner band of Baillerger)
o Outer band of Baillerger in the primary visual cortex bordering the calcarine sulcus is greatly expanded and is called the stria of Gennari
o In most regions of the neocortex, there are many radially oriented bundles of axons passing between the subcortical white matter and various parts of the cortex or between inner and outer cortical layers
o Cortical arousal and wakefulness is partially regulated by inputs from the thalamus, locus ceruleus, and basal nuclei |
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Term
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Definition
o Cytoarchitecture of cortex differs from one area to another in ways that are related to function (Fig. 32-7)
o Heterotypical granular cortex – layer IV, the major input layer is thick, whereas layer V, the major projection layer, is narrow and indistinct; found in primary sensory cortex
o Heterotypical agranular cortex – layer IV, the major input layer, is almost invisible and layer V, the major, the major projection layer, is very thick and seeming to merge with layer II; found in primary motor cortex
o Homotypical cortex – all six layers are clearly represented and are of roughly equal thickness; found in most areas of the neocortex, including the association cortices
o Korbinian Brodmann subdivided the cerebral cortex on the basis of cytoarchitectural differences into 47 distinct areas |
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Term
| • Higher Cortical Functions |
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Definition
o The cerebral cortex is generally considered to be the seat of higher intellectual functions
o The cerebral cortex can be divided into four general functional categories (Fig. 32-12):
Sensory – except for olfaction, receive thalamocortical fibers from diencephalic relay nuclei that are functionally related to each modality
a) Primary somatosensory cortex (Brodmann areas 3, 2, and 1) receives projections from the ventral posterior complex of thalamus; projects to Brodmann area 5
b) Primary visual cortex (Brodmann area 17) receives projections from the lateral geniculate nucleus; projects to Brodmann area 18 & 19
c) Primary auditory cortex (Brodmann areas 41 & 42) receives projections from the medial geniculate nucleus; projects to Brodmann area 22
Unimodal association cortices – adjacent to each primary sensory area devoted to a higher level of information processing relevant to that specific sensory modality
a) Visual unimodal association cortices (Brodmann areas 18, 19, 20, 21, and 37)
b) Somatosensory association cortex (Brodmann area 5)
c) Auditory association cortex (Brodmann area 22)
Motor
Multimodal association cortex – receive information from several different sensory modalities and create a complete experience of our surroundings; critical to our ability to communicate using language, to reason to extrapolate future events on the basis of present experience, to make complex and long-range plans, and to imagine and create things that have never existed |
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Term
| • Dominant Hemisphere and Language |
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Definition
o The cerebral hemisphere that controls language is called the dominant hemisphere
o Vast majority of people have left cerebral dominance with brain lesions that adversely affect language being found in the left hemisphere in about 95% of cases
o Almost all right-handed individuals and about half of the left-handed individuals are left cerebral dominant; in most of the general population, the right cerebral hemisphere is non-dominant
o Language is the faculty of communication using symbols organized by a system of grammar to describe things and events and to express ideas; closely linked to vision and audition
o Aphasia – a disturbance of the comprehension and formulation of language, not a disorder of hearing, vision, or motor control; can affect verbal (spoken and written) and nonverbal (sign) language
o Some features of language are affected by lesions in the non-dominant parietal lobe; patients with right parietal lesion may have difficulty appreciating the prosody (variations in vocal inflections, emotional content, and melody that may alter the meaning of spoken sentence) of speech |
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Term
| o Broca aphasia (expressive aphasia or nonfluent aphasia) |
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Definition
) consists of a loss of the ability to speak fluently
o Lesions are located in the inferior frontal gyrus of the left hemisphere primarily Brodmann areas 44 & 45
o Most common causes are tumors and occlusions of frontal M4 branches of the middle cerebral artery
o Patients with the most severe form of Broca aphasia are unable to speak (mutism), although they are able to swallow and breathe normally and make guttural sounds and understand spoken language
o No paralysis of vocal apparatus, rather, it is a difficulty in turning a concept or thought into a sequence of meaningful sounds
o Full-blown Broca aphasia indicates that the damage extends beyond the Broca area of the cortex to include insular cortex and subjacent white matter
o Patients typically have contralateral motor signs and symptoms such as weakness (paresis) of the lower part of the face, lateral deviation of the tongue when protruded, and weakness of the arm–aphasia plus these motor problems suggests an occlusion of branches from the proximal parts of the middle cerebral artery (M1) including the lenticulostriate arteries
o In less severe cases and patients in recovery process, limited speech is possible
o Mild Broca aphasia indicates that the damage affects only cortical area
o Short habitual phrases such as “hi,” “fine, thank you,” and “yes” and “no” are the first to come back
o Speech is slowed and labored, enunciation is poor, and nonessential words are commonly omitted (telegraphic speech)
o Patients typically have difficulty with writing (agraphia) although they can understand written language |
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Term
| o Wernicke aphasia (receptive or fluent aphasia) |
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Definition
primarily a defect of the comprehension rather than expression of language
o Lesions are located in the supramarginal and angular gyri (Brodmann areas 37, 39, and 40) and posterior part of the superior temporal gyrus (Brodmann area 22) in the left hemisphere
o May result from occlusion of temporal and parietal M4 branches of the middle cerebral artery; hemorrhage into the thalamus (or tumors in the thalamus) extending laterally and caudally to invade the subcortical white matter
o If damage impinges on the Meyer loop and interrupts the optic radiations, a contralateral homonymous hemianopia may occur
o Patients with severe Wernicke aphasia are unable to understand what is said to them, are unable to read (alexia), are unable to write comprehensible language (agraphia) and display fluent paraphasic speech (the ability to produce clear, fluent, melodic speech at a normal or even faster than normal rate)
o Content of speech may be unintelligible because of frequent errors of word choice, inappropriate use of words, or use of made-up nonsense words (word salad) e.g. “we went to drive in the bridge for red pymarid were crooking the lawn browsers”
o Less severe cases, paraphasias occurs e.g. trying to say “the cat has claws” becomes “the cat has clads”–literal paraphasia–incorrect but similar-sounding word or “the cat has tires”–verbal paraphasia–word that seems appropriate to the patient but is incorrect
o Patient with Wernicke aphasia are much less aware of the extent of their disability compared to patients with Broca aphasia
o Damage to the basal nuclei, particularly to the head of the caudate on the left side, has been associated with language disorders similar to Wernicke aphasia |
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Term
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Definition
| a less common type of aphasia, results from interruption of the connections of linking the Broca and Wernicke areas; comprehension is normal and expression is fluent but the patient has difficulty translating what someone has said to him or her into an appropriate reply |
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Term
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Definition
| occurs when occlusion of the left internal carotid or the most proximal portion of the middle cerebral artery (M1) produces damage that encroaches on both the Broca and Wernicke areas, and the loss of language is virtually complete |
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Term
| • Contralateral Neglect (Hemineglect) and Related Symptoms |
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Definition
o Results in damage to the right parietal association cortex (non-dominant); patients will be completely unaware of objects and events in the left half of his or her surrounding space
o The parietal association cortex is the most highly lateralized in the brain with language functions concentrated in the left hemisphere and spatial relationships and related selective attention concentrated in the right hemisphere
o In its milder forms, contralateral neglect may simply be a tendency to ignore things on the left side of the patient’s surroundings
o In extreme cases, patients may not even recognize the left side of his or her own body (asomatognosia) e.g. ignore left side when dressing or grooming (dressing apraxia)
o Another group of symptoms associated with right parietal lobe lesions involves losing the ability to function successfully within the spatial surroundings e.g. unable to describe his/her route between home and work
o Another difficulty experienced by patients is the inability to successfully manipulate objects in space (constructional apraxia) e.g. duplicate a simple block construction while looking at a model
o Disorders of affect are also common such as reduced ability to understand and appreciate humor, loss of the ability to appreciate the prosody of speech, and often an inappropriate cheerfulness and lack of concern for, or even awareness of, the implications of the illness |
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Term
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Definition
a disorder of motor control that may occur after damage in parietal association cortex, premotor cortex, or supplementary motor cortex
No paralysis of individual muscles or limbs and muscle strength may be undiminished
Unable to coordinate his or her muscles to execute complex behavior e.g. patient who can visually recognize a hammer, can name it, can explain what it is used for, and has the strength to pick it up but will be unable to demonstrate how it is used to drive a nail into a board
May affect the muscles of speech; separate disorder from aphasia |
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