A line of cell ventral to the neural plate that will become the site of the vertebral column.

Remnants of the notochord are found in the nucleus pulposus of the intervertebral discs.

Cells arising from the neural fold during the invagination of the neural plate. As the neural plate becomes the neural tube, these cells will be pushed out to the dorsal sides, essentially surrouding the folding plate.

These will mostly form the dorsal roots, containing the sensory nerves.

Mesodermal tissue that is covered by ectoderm that appear as lumps on the dorsal side of the embryo. This shows the segmentation of the nervous system.

The mesoderm will develop in muscle, and will carry nerves (motor; ventral) that will relate back to the original developmental position = myotomes

The ectoderm will develop into skin, and will carry nerves (sensory; dorsal) that will relate back to the original delopmental position = dermatomes

.

• Olfactory
• Sensory: smell
• Directly off brain

• Optic
• Sensory: vision
• Directly off the brain

• Oculomotor
• Motor: iris (contracted), levator palpebrae, Eye muscles (except lateral rectus and superior oblique)
• Off of the midbrain

• Trochlear
• Motor: Superior Oblique
• Off of the midbrain

• Trigeminal
• Motor: muscles of mastication
• Sensory: facial sensation
• Off of the middle pons

• Abducens
• Motor: Lateral Rectus
• Off of the lower pons

• Facial
• Motor: facial expression
• Sensory: taste
• Off of the lower pons

• Vestibulo-cochlear
• Sensory: head position, acceleration, hearing
• Off of the lower pons

• Glossopharyngeal
• Motor: pharynx
• Sensory: taste
• Off of the medulla oblongata

• Vagus
• Motor & Sensory: Lung, Heart, Gut, Larynx
• Off of the medulla oblongata

• Spinal Accessory
• Motor: Trapezius and SCM
• Off the medulla oblongata and spinal cord

• Hypoglossal
• Motor: Tongue
• Off the medulla oblongata

Vertical pressure (perpendicular to the skin)

"Merkel is Vertical"

  Lateral pressure (parallel to the skin)

"M.C. Later(-al)"

Deep pressure

"Press roughly (deep)"

Deep vibrations

"Pa-pa-pa" vibrations

Transient signal interuption due to axon compression. No axonal degeneration/death.

Best case scenario.

Refers to damage in the PNS.

Axon is damaged by an extended pressure injury. The connective tissue is intact.

Has a better chance for regeneration than neurotmesis.

Refers to damage in the PNS.

Damage to both the axon and the connective tissue (complete cut/severence). Damage to the CT results in displacement of the severed nerve ends. Most severe situation, less chance for regeneration.

Regards to damage in the PNS.

• Neurofilaments swell and fragment.
• There is an increase in mitochondria, in an attempt to repair and clean up
• The myelin retracts from the axon

• The axon myelin becomes swollen and irregular

The forebrain (the most cephaled).

Develops into the:

1. Telencephalon
2. Diencephalon

Derived from the prosencephalon. Develops into:

• Cerebral hemispheres
• Lobes of the cortex
• The 2 lateral ventricles

A derivative of the prosencephalon. Develops into:

• The thalamus
• Hypothalamus
• 3rd ventricle

The midbrain. Remains the mesencephalon as development continues (doesn't "divide")

Cranial Nerves III & IV will arise from here.

The "Hindbrain". Divides into:

1. Metencephalon
2. Myelencephalon

A Rhombencephalon derivative. Develops into:

• Pons
• Cerebellum
• 4th ventricle

A Rhombencephalon derivative. Develops into:

• Medulla Oblongata

Nerves/neurons carrying motor information to the PNS (effectors).

"Efferents exit the CNS"

Single axon coming from body, single dendrite coming to the body. "Typical" neuron we draw/examine.

"Discrete" neurons

One long process dendrite --> axon with cell body "off" the process. Has central and periphery connections.

Ex: dorsal root ganglion cells: Ganglion holds the cell body, process is in both CNS and PNS.

A neuron whose threshold potential is > -40mV. This means it takes a larger stimulus to reach threshold and trigger an AP.

Clinically, this would present as sluggish behavior, slow deep tendoon reflex, etc.

A condition in which the [K+] in the ECF drops. This increases the tendency for K+ to leave the cell because the gradient has changed. This then causes the Vm to become more (-), making the cell hypoexcitable. (Remember that K+ influences Vm, while Na+ influences threshold)

This is a common in elderly patients using diuretics with BP medicine, as increased urine output "washes" out the ECF K+

• Free nerve endings: pain and temp
• Pacinian corpuscles: deep vibrations
• Ruffini's corpuscles: deep pressure

Pacinian and Ruffini corpuscles contribute to our sense of proprioception.

A component of the muscle spindle. Two types:

Bag - dynamic stretch sensor

Chain - static stretch sensor

The afferent nerve wraps around this fiber.

1. Tap the tendon
2. Stretches the spindle
3. The stretch is sensed by the afferent nerve (Ia fiber)
4. Afferent sends signal to spinal cord, where it synapses on the motor efferent
5. Motor efferent (Aα fiber) synapses onto the extrafusal fiber
6. The muscle contracts

Some of the afferent and/or efferent fibers involved in the DTR circut are damaged, but there are enough to still produce a (weakened) reflex.

This can be caused by damage to the nerves directly or a herniated disk that compresses the nerves leaving the spinal cord.

• Large diameter
• Motor fiber
• 120 m/sec

• Small diameter
• Pain and temperature
• 15 m/sec

• Small diameter
• Unmyelinated
• Pain and temperature
• 2 m/sec

• Large diameter
• Spindle afferents
• 120 m/sec

• Small diameter
• Pain and temperature
• 15 m/sec

• Small diameter
• Unmyelinated
• Pain and temperature
• 2 m/sec

• Droopy or closed eyelid
• Lose ability to move eye: down, in, up
• Lose iris control: fixed and dilated (relaxed)
• Resting position of eye: lateral

• Depending on where the lesion is, lose 1/3 to all of facial sensation
• Loss of chewing

• Loss of lateral eye movement
• Resting eye postion - medial

• Loss of facial expression: Bell's Palsy
• Some taste loss

• Hearing loss
• Balance loss

• Loss of pharynx control
• Changes in blood pressure and breathing
• Difficulty swallowing

• Motor loss: Pharynx and larynx, swallowing, speech, heart, gut, lungs
• Increased heart rate

• Motor: trapezius and SCM
• symptoms are easier to see with lesions to the spinal part of the nerve

• Tongue control
  • Easy to test - have patient stick out tongue. The tongue will deviate to the side of the affected lesion (ie: A right sided lesion - tongue deviates to the right)

1. Caudate Nucleus
2. Globis Pallidus
3. Putamen

These are involved in motor activity

It is the place where all sensory and motor tracts pass through from the spinal cord and brain.

Fibers run ventral-dorsal (down-up); as they move up into the cortex, the fibers fan out (corona radiata) to their appropriate destinations.

You can see the the cerebral aqueduct and superior colliculi.

Note that in the stained picture, the substantia nigra stains white.

A. Superior colliculus
B. Periaqueductal gray

C. Thalamus
D. Red nucleus (just lateral to CN III)

E. CN III

F. Cerebral aqueduct

G. Substantia Nigra

HIJ. Crus

        [image]

A. Periaqueductal gray

B. Inferior Colliculus -> resembles tennis racket

E. Substantia Nigra

I. Cerebral Aqueduct

        [image]

A. Cerebellum

B. Cerebral aqueduct --> 4th Ventricl

C. CN V

G. Pontocerebellar fibers

        [image]

B. 4th Ventricle -> key to determining the slice

E. Olives - appear squiggly when stained

F. CN XII - hypoglossal

G. CN IX - glossopharyngeal

G. CN X - vagus

H. Pyramids - corticospinal tract

          [image]

• Sensory decussation
• Motor decussation (below sensory)
• Can't see the 4th ventricle
• Start to notice transition into the spinal cord

• Short pools of nuclei
• Receives multiple sensory inputs
• Contains the Ascending Reticular Activating System (ARAS)
  • Contributes to the awake state and sense of awareness
• Suppresses Sensory information, namely pain
• Vital integrating centers
  • Cardiovascular, BP, HR, respiration, vomiting, walking, swallowing

It is hour glass shaped, with the cervial and lumbosacral regions being larger than the thoracic.

This is because the larger areas innervate much more than the thoracic:

C = upper extremity

LS = lower extremite

T= chest

Gray matter is the area of processing and modulation. It includes:

• internuncial neurons = the modulators
• motor neurons
• autonomic neurons
• tract cells - ascending, sensory cell bodies

3 horns, which contain specific nuclei:

• Dorsal horn
• Lateral horn
• Ventral horn

1. Substantia gelatinosa = pain suppression
2. Nucleus propius = pain

1. IMM (intermediomedial) cell column
2. IML (intermediolateral) cell column

Both have autonomic functions.

The lateral horn is most prominant in the thoracic region

1. Medial and Lateral motor nuclei - cell bodies and dendrites for Aα LMNs
2. Special nuclei: phrenic and spinal accessory

Lamina I, III, IV, and V

They are found in the dorsal horn.

Lamina IX. It contains the cell bodies of Aα LMNs

This is the most important lamina, and is located in the ventral horn.

Columns or nuclei:

Dorsal

Lateral

Ventral

• Movement
• Muscle tone
• Visceral functioning
• Sensory editing (ex: pain suppression)

• Touch
• Pressure
• Pain
• Temperature
• Proprioception

• Fasiculus gracilis (most medial tract) = lower limb, sensory
• Fasiculus cuneatus (lateral to FG) = upper limb, sensory

[image]

• Lateral corticospinal
• Spinothalamic (lateral)

[image]

• Ventral (medial) corticospinal - minor to the lateral
• Spinothalamic (ventral/anterior)

It has big "wings" of gray matter. You can also see both the Fasiculus gracilis (N) and fasiculus cuneatus (O). (this is the only place you will see both, since FC carries sensory information from the upper limb)

[image]

The lateral horns are most prominant here, since the ANS information is primarily visceral organs, located in the thoracic region.

Additionally, there will be very little gray matter; mostly white matter

[image]

There is a more prominant butterfly gray, and you can see FG. There is still a fair amount of white matter.

[image]

There is a larger amount of gray matter than white matter. This is because there is only tracts from the lower limbs, fewer ascending and descending tracts are need.

[image]

Multiple nerve roots

[image]

• Scar tissue can make it difficult for sprouts to find and/or reach the tube.
• The wrong type of nerve sprout may end up in the wrong tube, thereby making that a non-functional regeneration (ie: A sensory nerve sprout finds a motor tube)
• The size of the gap. More than a few mm will hinder regeneration

1. Reinstatement of blood flow (only in neuropraxia, where there is only compression, no lesion of the neuron or CT)
2. Recovery of Synaptic Effectiveness (also only in neuropraxia)

Widespread CNS inhibition that occurs when there is an injury. There is no cell death, so it's analogous to neuropraxia. It seems that the CNS just "shuts down" these intact neurons.

Ex: concussion (contact injury); TIA (24 hrs post = complete recovery)

The cause of the inhibition is unclear. It may be: The hypothalamus, or the adjacent areas to the lesions, or changes in blood flow.

A recovery mechanism in which a lesion "awakens" neurons in a silent pathway. There are neurons in the brain that are silent, or "asleep". When a lesion occurs, it activates these neurons to help with regaining some function.

This also plays an important role in learning and memory. (Long term potentiation)

• Most will occur within the first 6 months post-injury (if they recover at all - some injuries or diseases have a downhill progression)
• There can be some recovery 6-12 months later
• And very little occurs after a year (although current research is starting to show this is not necessarily true)

It is not fully understood, but some theories include:

• Antigrowth factors produced by oligodendrocytes (Nogo), which are not produced by Schwann cells in the PNS
• A difference between the myelin and/or neural growth factors produced by Schwann cells and Oligodendrocytes
• Abscent growth factors in the CNS
• Immune response
• Too much scarring