Ventricular system and spinal nerve tracks

Question 1

Ventricular system

Answer 1

Lateral ventricle -> 3rd ventricle via left and right foramina of Monro

3rd ventricle -> 4th ventricle via cerebral aqueduct (of Sylvius)

4th ventricle -> subarachnoid space via

• Foramina of Luschka (Lateral)
• Foramen of Magendie (medial)

CSF made by ependymal cells of choroid plexus
Absorbed by arachnoid granulations and then drain into dural venous sinuses.

Question 2

Hydrocephalus:

Commincating hydrocephalus

Answer 2

Decreased CSF absorption by arachnoid granulation, increasing ICP, papillledema, and herniation (e.g. arachnoid scarring post meningitis)

Question 3

Hydrocephalus:

Communicating; normal pressure hydrocephalus

Answer 3

Results in increased subarachnoid space volume but no increase in CSF pressure

Expansion of ventricles distort the fibers of the corona radiata and leads to the clinical triad of:
Urinary incontinence
Ataxia,
Cognitive dysfunciton

“Wet, wobbly, and wacky”

Question 4

Hydrocephalus:

Communicating; hydrocephalus ex vacuo

Answer 4

Appearance of increased CSF in atrophy
(Alzheimer’s disease, advanced HIV, Pick’s disease)

ICP is normal; triad is NOT seen

Apperance increase in CSF observed on imaging is actually result of decreased neural tissue due to neuronal atropny

Question 5

Hydrocephalus:

Noncommunicating hydrocephalus

Answer 5

Caused by a structural blockage of CSF circulation

such as stenosis of the aqueduct of Sylvius.

Question 6

Spinal nerves

Answer 6

31 spinal nerves: "Just like B&R ice cream"
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal

Nerves C1-7 exit above the corresponding vertebrae, whereas all below.

Vertebral disc herniation: nucleus pulposus (soft central disc) herniates through anulus fibrosus (outer ring); usually occurs posterolaterally at L4-L5 or L5-S1.

Question 7

Spinal cord-lower extent

Answer 7

In adults, spinal cord extends to lower border of L1-L2 vertebrae.

Subarachnoid space (which contains CSF) extents to lower border of S2 vertebrae

Lumbar puncture dune at L3-4 or L4-5.

Question 8

Spinal cord and associated tracts

Answer 8

Dorsal columns: pressure, vibration, touch, proprioception

• Comprised of fasciculus cuneatus (upper body, extremities) and fasciculus gracilis (lower body, extremities)
• Supplied by posterior spinal artery

Lateral spinothalamic tract: pain and temp

Posterior horn (gray matter)

Lateral corticospinal tract: voluntary motor
- Legs are lateral in lateral corticospinal, spinothalamic tract.

Intermediate horn sympathetics (T1-L2/L3)

Anterior spinothalamic tract (crude touch, pressure) in gray matter.

• Medial (cervical) to lateral (sacral)
• cross anterior white commissure

Anterior horn (gray matter)

Anterior spinal artery.

Question 9

Spinal tract: dorsal column

*ascending tracts synapse and then cross

Answer 9

Medial lemniscal pathway
Ascending pressure, vibration, fine touch, and proprioception

1st order neuron: sensory nerve endings -> cell bodies in dorsal root ganglion -> enter spina cords, ascent ipsilaterally in dorsal column

Synapse 1: ipsilateral nucleus cuneatus or gracilis (medulla)

2nd order neuron: Decussate in medulla -> ascends contralaterally in medial lemniscus

Synapse 2: VPL (thalamus)

3rd order neuron:sensory cortex

Question 10

Spinal tract: spinothalamic tract

*ascending tracts synapse and then cross

Answer 10

Lateral: pain and temp
Anterior: crude touch, pressure

1st order neuron: sensory nerve ending (A-delta and C fibers) cell bodies in dorsal root ganglion -> enters spinal cord

Synapse 1: ipsilateral gray matter (spinal cord)

2nd order neuron: decussates at anterior white commisure -> ascends contralaterally

Synapse 2: VPL (thalamus)

3rd order neuron: sensory cortex.

Question 11

Spinal tract: lateral corticospinal tract

*ascending tracts synapse and then cross

Answer 11

Descending voluntary movement of contralateral limb

1st order neuron: UMN cell body in 1’ motor cortex -> descend ipsilaterally (through internal capsule) until decussating at caudal medulla (pyramidal decussation) -> descends contralaterally

Synapse 1: cell body of anterior horn (spinal cord)

2nd order neuron: LMN: leaves spinal cord

Synapse 2: NMJ

Question 12

Motor neuron signs

Answer 12

Lower MN: everything lowered (less muscle mass, lower muscle tone, lower reflex, downgoing toes)

Upper MN: everything up (tone, DTR, toes)

Fasciculation is muscle twitching
Babinski is normal in infants

Question 13

UMN lesion

Answer 13

Weakness
Increased reflex
Increased tone
Positive babinski
Spastic paralysis
Clasp knife spasticity

Question 14

LMN lesions

Answer 14

Weakness
Atrophy
Fasciculation
Decreased reflex
Decreased tone
Flaccid paralysis