Spinal Cord - function and dysfunction

Question 1

How many spinal nerves are there and how many vertebrae?

Answer 1

31 nerves

33 vertebrae

Question 2

Where are there enlargements in the spinal cord and why?

Answer 2

C3-T1 (extra motor neurones that go to the muscles of the upper back)
L1-S3 (extra motor neurones going to the muscles of the lower limbs)

Question 3

If the spinal cord was severed below the lumbosacral region what would happen?

Answer 3

affect bladder and bowel control

Question 4

What would a lesion above C3-C5 affect?

Answer 4

breathing ability

Question 5

What is paraplegia?

Answer 5

loss of voluntary control of the lower limbs

Question 6

Describe how the spinal cord and vertebral column are different in terms of when they stop developing

Answer 6

spinal cord stops early but VC develops into adulthood

Question 7

What are the three layers of meninges covering the spine?

Answer 7

dura
arachnoid
pia

Question 8

What are the denticulate ligaments?

Answer 8

Small protrusions of pia mater that tether the spinal cord.

Question 9

What is special about the extradural space in the spinal cord?

Answer 9

• There is a unique extradural space between the outside of the dura and the bone (not in cranial meninges)
• The space is full of venous plexuses and fatty tissue
• This space is used clinically to inject anaesthetic

Question 10

Where does an epidural go?

Answer 10

extradural space - longer time when duration unknown e.g. during childbirth

Question 11

Where does a spinal block go?

Answer 11

subarachnoid space - short term e.g for surgeries with known duration

Question 12

During injuries which part of the spinal cord is most important?

Answer 12

White as it carries axons

Question 13

What is syringomyelia?

Answer 13

Caused by an enlargement of the central canal - cyst formed within sc

Question 14

What is a dermatome?

Answer 14

An area of skin supplied by a single spinal nerve or spinal segment (stripes)

Question 15

What is a myotome?

Answer 15

Muscle supplied by a single spinal nerve or spinal segment

Question 16

What is a ramus?

Answer 16

Branching from a root

Question 17

What is a rootlet?

Answer 17

Division of a root attaching the spinal cord

Question 18

Name some parts of the spinal cord

Answer 18

posterior and anterior column (aread next to the horns (medial))

posterolateral and anterolateral sulcus (exit/entry point for the motor and sensory root)

anterior median fissure (deeper hence fissure)

posterior median sulcus (less deep hence sulcus)

Question 19

What are ascending and descending motor tracts?

Answer 19

ascending - sensory

descending - motor

Question 20

What are the three most important tracts in the spinal cord and what are they important for?

LOOK AT DIAGRAM TO SEE LOCATION

Answer 20

Lateral Corticospinal Tract

• MOTOR
• Important for fine movements

Dorsal Columns

• SENSORY
• Touch, vibration, pressure

Spinothalamic Tract

• SENSORY
• Pain, temperature

Question 21

What are the two main stages of injury to the lateral corticospinal tract?

Answer 21

Stage 1 - spinal shock

Stage 2 - return of the reflexes

Question 22

What happens during stage 1?

Answer 22

• You lose all reflex activity below the level of the lesion - there is no direct damage to them, they just stop working
• Causes flaccid paralysis - the limbs become floppy and there is very little muscle tone
• Eventually this changes and the reflexes come back with a vengeance

Question 23

What happens during stage 2?

Answer 23

• Hyperreflexia
• E.g. if you test the knee-jerk reflex the leg will go mad
• You also get spasticity where the patient experiences spontaneous muscle contraction
• There is very high muscle tone - rigid paralysis
• This is probably because the lower motor neurones below the level of the lesion have been cut off from their normal activating pathway so they have lowered their threshold and become more sensitive

Question 24

What is important in determining the extent and location of damage done via unilateral lesions?

Answer 24

the place where the tract decussates (crosses over)

Question 25

Where does the lateral corticospinal tract neurone decussate?

Answer 25

at medulla

Question 26

If there is a unilateral lesion in the mid thoracic region of the corticospinal tract where will the deficit be?

Answer 26

same side as the lesion

Question 27

Where do the sensory neurones going into the dorsal columns (sensory) decussate?

Answer 27

At the level of the medulla

Question 28

Where do pain nerves cross over?

Answer 28

Immediately as the enter the spinal cord - when the neurone enters the dorsal horn it synapses and then the second cell sends its axon across the midline

Question 29

If there is a left sided unilateral lesion at midthoracic level in the spinothalamic tract, what will happen to the legs?

Answer 29

It will not interrupt the spinothalamic tract coming from the left leg but it will interrupt the spinothalamic tract that’s going up the left side and coming from the right leg
In this case, a lesion on the left will cause loss of pain sensation in the right leg

Question 30

What is syringomyelia?

Answer 30

• Loss of temperature sensation in the arms but not the legs is caused by the formation of a space in the spinal cord called a syrinx
• Enlargement of the central canal

Question 31

What does syringomyelia damage and why aren’t the legs affected?

Answer 31

• There is a large space in the middle that is selectively damaging the spinothalamic axons that are crossing over at the level of the lesion but it does not affect the fibres that have already crossed over and are travelling up in the spinothalamic tract
• The fibres from the legs would already have crossed over and would be travelling up the spinothalamic tract unhindered