2. Spinal cord function and dysfunction

Question 1

How many pairs of spinal nerves are there and what are their regions?

Answer 1

31 spinal nerve pairs
8 Cervical
12 Thoracic
5 lumbar
5 sacral
1 coccygeal

Question 2

How do nerves leave?

Answer 2

Motor neurons in ventral horn and they emerge from the vertebral column through intervertebral foramina

Question 3

What are the enlargements of the spinal cord and what significance do they have?

Answer 3

Cervical enlargement at c4-t1, has extra motor neurons to go to upper limbs muscles
Lumbar enlargement at L1-s3 has extra motor neurons that go to lower limbs muscles

Question 4

Describe the discrepancy between spinal nerves and vertebral levels

Answer 4

After c7 the spinal nerves emerge below their correspondent vertebral level.
Spinal cord stops at t12/l1 and spinal nerves travel longer distances down to under their vertebral level.

Question 5

What are the small protrusions of the pia mater called and what are their functions?

Answer 5

Denticulate ligaments

They anchor the pia mater to the dura mater, lateral denticulate ligaments separate the anterior and posterior roots

Question 6

Describe the epidural space

Answer 6

True space between the dura and the vertebral periosteum filled with fat and venous plexus

Question 7

Contrast the anterior and posterior roots of the spinal cord

Answer 7

Posterior root carries sensory information, cell bodies are in spinal ganglion, enters spinal cord in posterolateral sulcus
Anterior root carries motor information exits at anterolateral sulcus

Question 8

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

Answer 8

Epidural space

This can be used for injecting anaesthetics

Question 9

What tissue bridges the spinal cord to the sacrum?

Answer 9

Filum terminale

Question 10

What is the consequence of a lesion above C3-5

Answer 10

No breathing

Question 11

Compare epidural block and spinal nerve block

Answer 11

Epidural is in the epidural space and allows medication to be fed through. Spinal nerve block is in subarachnoid space and used for a single injection of anaesthesia

Question 12

What are the contents of grey and white matter?

Answer 12

White matter (out) - tracts 
Grey matter (in) - cell bodies

Question 13

How can you recognise which vertebral level you are at from the spinal cord?

Answer 13

Cuneate fasciculus is found only in the cervical tract it’s bigger than gracilis as more fine touch than lower limbs.
More grey matter in lumbar vertebrae
gracile fasciculus is found at all levels
substantia gelatinosa and intermediolateral columns are found in lateral aspects of thoracic column

Question 14

What is paraplegia?

Answer 14

Loss of voluntary control of lower limbs

Question 15

What are the three important tracts in spinal cord injury and what are their roles?

Answer 15

Lateral corticopsinal tract - fine motor movements
Dorsal columns - touch pressure, vibration, propioception
Spinothalamic tract - pain and temperature

Question 16

What are the two stages of lateral corticospinal tract damage?

Answer 16

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 paralys

Question 17

Where do the upper motor neurons within the lateral corticospinal tract decussate?

Answer 17

Pyramidal decussation in the medulla

Question 18

If you have a unilateral lesion of the lateral corticospinal tract in the mid-thoracic region, where will the deficit be?

Answer 18

Ipsilateral – on the same side as the lesion because the fibres decussate at the pyramidal decussation in the medulla

Question 19

Where do the sensory fibres of the dorsal columns decussate?

Answer 19

Sensory decussation in the medulla

medial lemniscus

Question 20

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

Answer 20

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

Question 21

What is syringomyelia? Describe and explain its features

Answer 21

Enlargement of the central canal (the space is called a syrinx)
This selectively affects the spinothalamic fibres that are crossing at the level of the lesion and it does not affect fibres that have already crossed
So if the enlargement of the central canal is in the region of the cervical enlargement, you could get loss of pain/temperature sensation in the arms but not the legs (because those fibres would already have crossed and would be ascending in the spinothalamic tract away from the central canal)

Question 22

Which factors affect severity of spinal lesion?

Answer 22

Loss of neural tissue
Vertical Level - higher level the greater the disability
transverse plane

Question 23

Describe neural tissue loss

Answer 23

Usually small if due to trauma
More extensive if metastases or degenerative disease
MRI of degenerating spinal cord

Question 24

Which areas of spinal cord involved in dorsal columns?

Answer 24

Fasciculus gracilis and cuneatus

Question 25

What is Brown-sequard syndrome?

Answer 25

A lesion in the spinal cord which causes paralysis/weakness in one side (hemiparaplegia) and loss of sensation in the other side (hemianesthesia)