2 - Spinal Chord Function and Dysfunction

Question 1

What is a spinal segment?

Answer 1

a portion of the spinal chord that gives rise to a pair of spinal nerves

Question 2

How many spinal nerves (pairs)/segments are there?

Answer 2

31

Question 3

Describe the discrepancy between the levels of the vertebral levels and the spinal levels

Answer 3

as you descend down the spinal chord, the vertebral level (the place where the nerve emerges from the vertebral column) becomes progressively more inferior than the spinal level (the place where the nerve emerges from the spinal chord)

Question 4

Describe the relationship between the bones of the vertebral column and their corresponding nerves

Answer 4

above C8, the corresponding nerve emerges from above the vertebra
(7 cervical vertebra and 8 cervical nerves)
below C8, the corresponding nerve emerges from below the vertebra

Question 5

What are the two enlargements in the spinal cord and what is their significance?

Answer 5

Cervical enlargement (C4-T1) – has extra motor neurons that go to the muscles of the upper limb
Lumbosacral enlargement (L2-S3) – has extra motor neurons that go to the muscles of the lower limb

Question 6

What are the layers of the meninges?

Answer 6

dura mater - outermost layer
arachnoid mater
(arachnoid and dura are closely associated)
SUB ARACHNOID SPACE - CSF is found here
pia mater

Question 7

Which space is present in the spinal meninges but not in the cranial meninges?

Answer 7

Epidural space – this can be used for injecting anaesthetics/analgestics

Question 8

Define dermatome

Answer 8

an area of skin innervated by (a pair) one single spinal nerve or spinal segment

Question 9

Define myotome

Answer 9

muscles innervated by (a pair) one single spinal nerve or spinal segment

Question 10

When does a spinal nerve form?

Answer 10

when the ventral and dorsal horns have fused (before the rami branch off)
they have a mixture of sensory and motor nerves

Question 11

Which is larger out of the anterior and posterior rami?

Answer 11

anterior

Question 12

What are the three most important tracts in spinal cord injury? State their roles.

Answer 12

Lateral corticospinal tract – fine motor movements (motor)
Dorsal columns – fine touch, pressure, vibration, proprioception (sensory)
Spinothalamic tract – pain and temperature (pain)

Question 13

Where do the upper motor neurons within the lateral corticospinal tract decussate (cross over)?

Answer 13

Pyramidal decussation in the medulla

Question 14

Usually, how many neurones in sensory pathways?

Answer 14

3
1 in skin, 1 in CNS and 1 going from the thalamus to the brain

2nd order sensory neurones cross over

Question 15

Where do the sensory fibres of the dorsal columns decussate?

Answer 15

Sensory decussation in the medulla

Question 16

How are pain neurons arranged differently to other sensory and motor neurons?

Answer 16

The first order neurons synapse in the dorsal horn and then the second order neuron crosses to the contralateral side immediately (at the level of the synapse with the first order neurone)
The second order neurons then ascend on the contralateral side

(dorsal crosses over in the medulla, hence ascends on the same side)

Question 17

Describe autonomic outflow in relation to spinal segments

Answer 17

parasympathetic outflow - (craniosacral) cranial nerves III, VIII, IX and X and S2-S4
sympathetic outflow - (thoracocolumbar) T1-L2

Question 18

What are the two stages of lateral corticospinal tract damage?

Answer 18

SPINAL SHOCK – you get loss of reflexes below the level of the lesion leading to flaccid paralysis. The limbs become floppy and there is little muscle tone
RETURN OF REFLEXES – you get hyperreflexia and spasticity. The patient experiences spontaneous muscle contraction and there is very high muscle tone – rigid paralysis

Question 19

at what vertebral level does the spinal chord end at?

Answer 19

L2

Question 20

What are are arachnoid granulations?

Answer 20

they are small protrusions of the arachnoid mater into the outer membrane of the dura mater. They protrude into the dural venous sinuses of the brain, and allow CSF to exit the subarachnoid space and enter the blood stream.