Term
| Dorsal Column-Medial Lemniscal Pathway |
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Definition
| Pathway carries discriminative tactile sensations from the body These include touch, pressure, 2-point discrimination, vibratory sense, stereognosis) and conscious proprioception (both position and movement sense). Afferent input is detected by cutaneous receptors (Pacinian corpuscles, Meissner's corpuscles, Merkel's disks, etc.), innervated by A-beta afferents. These afferents enter the spinal cord in the more medial regions of Lissauer's tract. |
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Term
| In the dorsal column these axons are termed... |
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Definition
| fasciculus gracilis (from the lower extremities) or fasciculus cuneatus (from the upper extremities). The peripheral axons, dorsal root ganglion somas and the dorsal column axons comprise the 1st order neurons of this ascending pathway. |
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Term
| The dorsal column axons terminate in the ______ as they synapse onto neurons in the nucleus _____ (LE) and nucleus ______ (UE). |
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Definition
the medulla, gracilis
Thus, these 1st order
DRG neurons (A-beta afferents) run all the way from the peripheral cutaneus receptor to the termination site in the medulla. |
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Term
| Axons that comprise the 2nd order neurons (Dorsal Column-Medial Lemniscal Pathway) |
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Definition
| Neurons in the nucleus gracilis and nucleus cuneatus project axons that ascend through the brainstem as the Medial Lemniscus. |
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Term
| The Medial Lemniscus crosses at the ______ and then goes to the ______ where it synapses. |
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Definition
| Medulla, thalamic neurons (ventral posterior lateral nucleus – VPL) |
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Term
| The 3rd order neurons (Dorsal Column-Medial Lemniscal Pathway) |
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Definition
| Thes thalamic neurons and their thalamocortical projections through the corona radiata to the primary somatosensory cortex (post-central gyrus; Brodmann's areas 1,2,3). |
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Term
| Trigmenial Lemniscal Pathways |
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Definition
| 1. Pathway carries discriminative tactile sensations from the face These include touch, pressure, 2-point discrimination, vibratory sense, stereognosis) and conscious proprioception (both position and movement sense). Afferent input is detected by cutaneous receptors (Pacinian corpuscles, Meissner's corpuscles, Merkel's disks, etc.), innervated by A-beta afferents. |
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Term
| Lateral Spinothalamic Tract (also called the Anterolateral System) |
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Definition
| Pathway carries pain and thermal sense from free nerve endings and heat and cold receptors in the skin of the body. |
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Term
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Definition
| Pathway carries pain and thermal sense from free nerve endings and heat and cold receptors in the skin of the face. |
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Term
| Dorsal Spinocerebellar Tract (DSCT) |
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Definition
| An uncrossed pathway carrying unconscious proprioceptive information to the cerebellum. |
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Term
| Spinocuneocerebellar Pathway (also called the cuneocerebellar pathway) |
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Definition
| An uncrossed pathway carrying unconscious proprioceptive information from the upper extremity. |
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Term
| Ventral Spinocerebellar Tract (VSCT) |
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Definition
This tract carries information to the cerebellum about the descending motor signals to thoracic and lumbar spinal cord.
2. Its originating neurons are diffusely located in lamina V, VI, and VII (not from a discrete nucleus such as Clarke's nucleus) of the thoracic and lumbar spinal cord |
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Term
| Rostral Spinocerebellar Tract |
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Definition
1. This tract carries information to the cerebellum about the descending motor signals to the cervical spinal cord.
2. Its originating neurons are diffusely located in lamina V, VI, and VII of the cervical spinal cord.
3. The axons from these neurons ascend ipsilaterally in the spinal cord and medulla.
4. These axons enter the cerebellum via both the inferior and superior cerebellar peduncles.
5. This tract, along with the ventral spinocerebellar pathway, is an internal feedback pathway that monitors corticospinal and brainstem-spinal signals to the spinal cord. |
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Term
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Definition
A protective mechanism that is normal, essential, healthy, and without it, the individual has the potential for serious injury or infection. It signals that tissue damage is imminent or has already occurred.
Acute pain can usually be localized to the site of tissue damage. |
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Term
| A goal of occupational and physical therapists is |
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Definition
| to lessen chronic pain, which may be caused by inflammation, arthritis, nerve entrapment, gun shot wounds, surgery, migraine, cancer, spinal cord injury, stroke, tumors, or other chronic pain syndromes. |
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Term
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Definition
i. Visceral pain is sensed by receptors (e.g., free nerve endings) located in the internal organs (e.g., gall bladder, kidney, stomach, gut, heart).
ii. Examples of pain-inducing stimuli that would be sensed by receptors in the viscera include gall stones, kidney stones, ulcer, and appendicitis, pain of angina due to ischemia of heart muscle. |
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Term
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Definition
i. This pain can be further subdivided into superficial pain and deep pain.
ii. Superficial pain is pain that arises from the skin (cutaneous free nerve endings)
a. For example: pain from pinprick or pinching or hitting the thumb with a hammer.
b. Two qualities accompany superficial pain: initial pain (A delta fibers) and delayed pain (c fibers) (see Echo Pain, below).
iii. Deep pain arises from connective tissue, bones, joints and muscles.
a. Deep pain does not have the fast vs. slow pain qualities of superficial pain.
b. It tends to be longer lasting and more "nagging". Examples include muscle cramp, headaches (e.g., from meninges). |
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Term
Somatic Pain receptors enter the dorsal horn of the spinal cord via...
And synapse where? |
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Definition
Lissauer's tract
In the substantia gelatinosa (Rexed's lamina II). |
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Term
| A-delta (Group III afferents) |
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Definition
i.. lightly myelinated
ii. faster conducting than C fibers
iii. lower threshold to stimulation than C fibers
iv. located throughout the body
v. Types of sensations they carry include: localized, sharp, stabbing pain that is transmitted rapidly, perceived rapidly, and disappears quickly. This is also called initial pain or fast pain. |
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Term
| C afferents (Group IV afferents) |
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Definition
i. unmyelinated; widely distributed
ii. slow conducting
iii. Types of sensations they carry include: diffuse burning, aching, and itching -- qualities that tend to linger after the initial stimulus has ended. C afferents carry slow pain or delayed pain. |
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Term
| Stimulation of Pain Receptors |
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Definition
A. Mechanical deformation (inducing a receptor potential, which at threshold becomes a series of action potentials)
B. Extreme heat
C. Chemicals
i. Acid (e.g., lactic acid following intense exercise can cause muscle pain)
ii. Potassium ions (e.g., leak out of cells at the site of damage)
iii. Prostaglandins (released at the site of damage). Aspirin and aspirin-like drugs inhibit synthesis of prostaglandins and can reduce pain and inflammation locally.
iv. Histamine (released at the site of inflammation)
v. Other substances (bradykinin, serotonin, etc.) |
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Term
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Definition
A. A-delta and C afferents together are responsible for the phenomenon of "echo pain", which is associated with superficial somatic pain from the skin.
B. Echo pain includes initial, or fast, pain, which is transmitted rapidly by myelinated A-delta afferents. This is followed by delayed pain, which is transmitted by the slower conducting unmyelinated C afferents.
Examples of echo pain
1. Needle stick. Initially feel sharp prick (initial or fast pain); then feel second sensation that is a dull type pain, different in quality to the initial sharp sensation.
2. Touch a hot object (e.g., iron or hot pan). Initially feel hot stimulus (which induces a flexor withdrawal reflex), then feel a secondary, delayed pain that is lingering, aching and burning. |
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Term
| Gate Theory of Pain Control |
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Definition
(Local, segmental control of pain transmission)
Example: Fear of going to the dentist may enhance pain that is felt, whereas an athlete playing in a football game may play the game while injured, tending to ignore the pain from the injury.
They suggested that collaterals of A-beta afferents and those of pain afferents (A-delta and C fibers) have antagonistic effects on cells of the substantia gelatinosa.
4. A-beta fibers could pre-synaptically inhibit the interneurons that receive input from pain afferents. Inhibition of these interneurons (which synapse onto neurons of the spinothalamic tract), would prevent transmission of action potentials along the pain pathway (spinothalamic tract).
5. The gate would be open if the lateral spinothalamic tract neurons were stimulated, and pain transmission would proceed to the thalamus and on to the somatosensory cortex. The gate would be closed if the large cutaneous afferents (A-beta) inhibited transmission of the spinothalamic tract.
6. Gate control theory provides the basis of conventional TENS treatment. Transcutaneous electrical nerve stimulation is thought to activate larger diameter peripheral nerve fibers (A-beta) to presynaptically inhibit pain afferents. Pain relief basically lasts for the duration that the stimulus is on, with little carry-over pain relief. |
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Term
| Descending System for Control of Pain: |
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Definition
Dampening transmission of noxious information at the spinal cord level
1. Neurons in the periventricular and periaqueductal gray matter of the reticular formation of the brainstem receive input from branches of the spinothalamic tract (called spinotectal and spinoreticular fibers).
2. Neurons in the periventricular and periaqueductal gray matter excite neurons in the medulla whose axons descend in the dorsolateral funiculus of the spinal cord and release the transmitters serotonin and norepinephrine which act to excite interneurons containing enkephalins. These enkephalin-containing interneurons are thought to presynaptically inhibit the release of substance P (the neurotransmitter of pain afferents) and therefore reduce transmission of painful stimuli to the spinothalamic tract.
3. Evidence for the existence of the descending pain control system comes from the effect of electrical stimulation of the gray matter around the 3rd and 4th ventricles (periventricular gray) and around the cerebral aqueduct (periaqueductal gray) which induces profound analgesia. Other sensations such as touch can still be perceived. |
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Term
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Definition
1. Stress increases the levels of circulating endorphin from the pituitary.
2. Endorphins reduce the amount of substance P released from pain afferents in the substantia gelatinosa, thereby reducing transmission of pain signals in the spinothalamic tract.
3. Stress-induced analgesia is thought to be the mechanism by which soldiers wounded in battle can continue to fight, and athletes who are injured during a sport can continue to play. It is also thought to be the mechanism underlying the "runner's high". |
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Term
| CHRONIC PAIN – “Plasticity gone awry” |
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Definition
Persists for a prolonged period of time and tends to recur. Chronic pain serves no real useful function unless tissue damage is ongoing. Usually, it does not signal impending or recent tissue damage. It is sometimes difficult to pin point any physical disorder or derangement of tissue.
II. There is an affective (emotional) component to chronic pain in that it can induce anxiety (e.g., the patient worries that something very serious is causing the pain such as a cancer). Chronic pain can induce depression in some individuals. It can also lead to feelings of hopelessness, even to the point of suicidal feelings in some. Different types of people deal with pain differently.
III. Chronic pain can lead to pain neurosis, where pain can become the center of a person's life.
IV. Two basic forms of chronic pain: persistent somatic pain and neurogenic pain. |
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Term
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Definition
A. Peripheral stimulus persists in duration.
B. Inflammatory response to strong chemical, thermal, or mechanical stimuli of peripheral tissues.
C. Pain experience induces sensitization of peripheral nociceptors and/or sensitization of postsynaptic receptors (i.e., those on spinothalamic tract neurons) in the dorsal horn.
D. Plastic pathophysiological changes occur.
E. There may be a reinforcing nociceptive barrage from the periphery.
Examples: arthritis and certain cancers. |
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Term
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Definition
A. Also called "neuropathic pain" or "deafferentation pain".
B. Occurs following insult to peripheral or central nervous system tissues (along the pathway from the peripheral nerve to the spinothalamo-cortical system to the cerebral cortex).
C. There is loss of normal pain and temperature sensitivity, and the reaction to normal pain and thermal stimuli are exaggerated.
D. Neurogenic pain does not require continual afferent barrage to occur.
E. Examples of neurogenic pain include phantom pain (see below) and pain that follows brachial plexus avulsion.
F. Two types of neurogenic pain: Steady Neuropathic Pain and Peripherally Evoked Neuropathic Pain |
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Term
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Definition
a. This is the most common form of neurogenic pain, and has a burning quality to it.
b. Pain is thought to derive from degenerative and metabolic changes in the postsynaptic neurons (i.e., spinothalamic tract neurons) which become hyperactive.
c. Painful deafferentation dysesthesias are thought to be due to plastic changes central to the site of lesion. |
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Term
| Peripherally Evoked Neuropathic Pain |
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Definition
Receptors on the postsynaptic neurons become sensitized to input from a variety of cutaneous afferents, giving rise to sensory abnormalities of:
- allodynia (painful response to light touch) or
- hyperalgesia (decreased threshold and excessively painful response to normally mildly painful stimuli).
- paresthesia (abnormal sensation in the absence of nocioception).
- dysesthesia (evoked or spontaneous unpleasant abnormal sensation). |
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Term
| Chronic neurogenic/neuropathic pain is produced by: |
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Definition
A. Central sensitization
B. Structural reorganization
C. Ectopic foci
D. Ephaphtic transmission
E. Altered modulation |
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Term
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Definition
a. Damage to peripheral tissues causes the sensation of pain in response to subsequent stimuli to be enhanced.
b. The threshold of firing of nociceptors decreases (takes less stimulation to activate nociceptors) following injury.
c. Neighboring nociceptors (in areas previously undamaged) become sensitized and their threshold for activation also decreases (called secondary hyperalgesia).
Example: Causalgia and Complex Regional Pain Syndrome (CRPS) |
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Term
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Definition
| Following peripheral nerve injury or, less commonly, after a viral infection, activity of efferent fibers of the sympathetic nervous system can trigger sensation of burning pain, possibly by direct activation of nociceptive afferents or by nonsynaptic electrical cross-talk |
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Term
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Definition
| is described as progressively prolonged discharge of dorsal horn neurons to repeated input from nociceptors. |
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Term
| Structural Reorganization |
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Definition
1. Potent stimulation of pain afferents signals the CNS that injury has occurred.
2. If the pain signal is massive enough and prolonged enough, plastic and long-lasting changes occur in postsynaptic neurons of the spinothalamic tract in the dorsal horn of the SC.
3. Neurons of the spinothalamic tract become sensitive to ALL types of afferent input (pain and temperature as well as touch).
A. C-fiber axons withdrawal axon terminals while other types of axons, including A-Betas sprout collaterals to form new synapses on spinothalamic neurons in the substantia gelatinosa |
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Term
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Definition
| Myelin damage in A delta fibers allows for the excitation of these fibers at sites proximal to the peripheral nocioceptor, causing activation of the spinothalamic pathway in the absence of painful stimuli. |
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Term
| Ephaphtic transmission (crosstalk) |
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Definition
| A delta and C fibers become excited by neighboring cutaneous and proprioceptive axons/somas |
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Term
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Definition
| Deficits in the descending pathways that modulate pain decrease inhibitory input to the spinothalamic neurons, result in increased activity of the spinothalamic pathway. |
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Term
| Phantom Pain/Phantom Sensation |
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Definition
sensations are perceived by most amputees to be emanating from the amputated body part. (May also be phantom limb, phantom breasts following mastectomy, phantom genitalia following castration, phantoms of the entire lower body following spinal cord transection). Some 35% of amputees experience phantom pain, which is a type of chronic pain.
2. Types of sensations include warmth or cold, heaviness, cramping, or shooting, burning, crushing pain.
3. Phantom pain may appear immediately following surgery, or may appear weeks, months, or years later.
4. For the amputated upper extremity, a common sensation is that the hand is clenched, with the fingers bent over the thumb, digging into the palm so that the whole hand is tired and painful.
5. Causes for phantom pain are not well understood. It may be due to stimulation of peripheral nerves (e.g., a neuroma present near stump that continues to be stimulated accidentally) or to stimulation of autonomic nerves (the latter is an RSD-like phenomenon).
6. Another hypothesis for phantom pain is that nerve cells in the denervated areas of the spinal cord and brain, including somatosensory cortex, thalamus as well as other areas that formerly represented the limb fire spontaneously at high levels and with abnormal bursting patterns. |
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Term
| Treatments for Chronic Pain |
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Definition
1. Surgery
2. Dorsal column stimulation (thought to release endorphins/enkephalins to block pain)
3. Pharmacological agents (some can be addictive)
4. Physical treatment modalities
5. Acupuncture for pain. Stimulation of acupuncture points is thought to induce analgesia, (but perhaps not deep enough for surgery). Is successful in treatment of chronic pain for some people.
6. Nerve block injections, especially to block sympathetic nerve activity (see causalgia and reflex sympathetic dystrophy, below).
7. There is a definite psychological component to pain such that patients do better when they receive the treatment they want. |
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Term
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Definition
1. Afferents from viscera and afferents from dermatomes converge on same neurons in the dorsal horn of SC for transmission along the spinothalamic tract.
2. In some types of referred pain, the CNS tends to misinterpret the sensory information coming from viscera as coming from dermatomes. The brain has learned that pain generally comes from the somatic structure rather than the visceral structure.
Example 1: Angina
A. due to myocardial ischemia
B. pain is referred to the chest wall, left axillary region and inside the left arm, corresponding to the T1 and T2 dermatomes
C. Referred pain may be carried by afferents of blood vessels--this is not certain.
Example 2: Inflammation of diaphragm
A. May occur following laparoscopic surgery in which the abdominal cavity is inflated with a gas to enable the surgeon to explore with laparoscopic instruments. The gas irritates the diaphragm.
B. Pain is referred to the shoulder region, specifically to the C3, C4, and C5 dermatomes.
C. The motor and sensory innervation of the diaphragm is via segments C3, C4 and C5.
Other Examples:
Gallbladder pain referred to the scapular region
Ureteral pain referred to abdominal wall (kidney stone)
Bladder pain referred to perineum
Appendix pain (appendicitis) referred to anterior abdominal wall, around umbilicus |
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Term
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Definition
. Pain may be projected into areas that are innervated by nerves that are compressed or damaged at a distant site.
2. Pain is usually projected to a site distal to the actual site of injury, but not proximal to it. Example: With a shoulder injury, projected pain may be in elbow or wrist, but wrist pain would not be projected to the shoulder).
Example: A spinal nerve can be compressed at its point of entry into the spinal cord by damage to the intervertebral disk at that level (herniated disk). Pain impulses may radiate or project into areas supplied by the compressed spinal nerve (radiating pain in the buttocks and down the back of the thigh). |
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Term
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Definition
When a noxious stimulus acts on sensory neurons for a long period of time, the result is spontaneous pains that occur in waves or sudden attacks. Neuralgic pains tend to be restricted to regions supplied by the affected nerve or nerve root.
Example: Trigeminal neuralgia also called tic douloureux or intractable facial pain. This debilitating disorder is twice as common in females than males. Symptoms include shooting pain along one or more branches of CN V. Usually the maxillary and mandibular branches are involved. Pain occurs in bouts, remits, then recurs. Bouts of pain become progressively longer and remissions shorter. Cause is unknown. Herpes zoster (shingles) virus can infect the trigeminal nerve (as well as the spinal nerves), leaving the patient with trigeminal neuralgia. |
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