2. Spinal cord function and dysfunction

Question 1

How many pairs of spinal nerves are there (including different levels)?

Answer 1

• Total: 31
• Cervial - 8
• Thoracic - 12
• Lumbar - 5
• Sacral - 5
• Coccygeal - 1

Question 2

Which part of the vertebral column do nerves leave?

Answer 2

Intervertebral foramina

Question 3

How many cervical vertebrae are there and where do the cervical nerves leave in reference to the corresponding vertebra?

Answer 3

• 8 cervical nerves (7 vertebrae)

* Leave above the vertebrae

Question 4

Where are there extra neurones in the spinal cord?

Answer 4

Cervical enlargement (C3-T1)
• extra motor neurones to upper limb muscles

Lumbosacral enlargement (L1-S3)
• extra motor neurones to the lower limb muscles

Question 5

What would happen if the spinal cord was severed just below the lumbosacral enlargement?

Answer 5

• Stop motor command from brain to bladder and biowel

* Incontinence (lack of voluntary control over urination or defecation)

Question 6

What would happen if there was a lesion in the mid-thoracic region?

Answer 6

Paraplegia - loss of voluntary control of the lower limbs

Question 7

What would happen if there was a lesion above C3-C5?

Answer 7

Stop breathing - pathway to diaphragm disrupted

Question 8

Where can CSF be sampled from and why?

Answer 8

• Lumbar cistern
• Spinal cord stops growing early but vertebral keeps on growing into adulthood
• Larger subarachnoid space with CSF

Question 9

What are the three layers of the meninges of the spinal cord?

Answer 9

• Dura matter
• Arachnoid matter
• Pia matter

Question 10

How is the spinal cord held in the middle of the subarachnoid space?

Answer 10

Protrusions of the pia matter - denticulate ligaments

Question 11

How is the epidural space different in the cranial meninges compared to the spinal?

Answer 11

• Space in cranial meninges is only pathological and not normally appreciable
• Space in spinal cord is full of venous plexuses and fatty tissue
• This is because there are 2 layers of the dura (periosteal and inner meningeal) in the spinal cord, but the inner meningeal is lost as the medulla passes through the foramen magnum

Question 12

Why is the epidural (extradural) space clinically useful?

Answer 12

• Full of venous plexuses and fatty tissue

* Can inject anaesthetic

Question 13

What is formed where the two layered dura splits in the brain and why is this structure important?

Answer 13

• Sinuses

* Important for venous drainage and reabsorption of CSF into blood

Question 14

Where is a spinal block used and why?

Answer 14

• Local anaesthetic injected into subarachnoid space

* Usually used instead of general anaesthetic e.g. if patient is elderly

Question 15

Why are the dermatomes of the limbs more complicated than the thorax?

Answer 15

• Rotate as they develop

* Discrepancy between vertebral and spinal levels as you go down

Question 16

What information passes through the ventral root of the spinal cord?

Answer 16

Motor information comes out

Question 17

What information passes through the dorsal root of the spinal cord?

Answer 17

Sensory information comes in

Question 18

What do the rami contain and which is larger?

Answer 18

• Motor and sensory fibres

* Anterior ramus is larger

Question 19

Describe a cross section of the spinal cord?

Answer 19

Surface
• Posterior median sulcus
• Posterolateral sulcus - entry of dorsal root
• Anterolateral sulcus - exit of ventral root
• Anterior median fissure
• An
Outer
• Posterior column
• Lateral column
• Anterior column
Inner
• Posterior horn
• Inner horn

Question 20

How is the anterior median fissure different to the sulci?

Answer 20

Larger

Question 21

Describe the crossing over of the sensory neurones.

Answer 21

• Tend to cross over when they synapse
• Either synapse immediately and cross over at the level they entered, or travel up the dorsal column then cross over when they synapse in the medulla
• Fine touch and proprioception goes up without synapsing, until medulla
• Pain and temperature synapses then crosses up (may go up/down 1-2 segments before synapsing in the dorsal horn)

Question 22

Describe the crossing over of the motor neurones.

Answer 22

• Crossing over occurs in the medulla - decussation of pyramids
• Leaves on the side of the spinal cord it came down

Question 23

Describe the corticospinal tract?

Answer 23

• Voluntary movement pathway
• Lateral - limbs
• Anterior - trunk (proximal muscles)
• Starts in motor cortex
• Synapses (only once) in ventral horn of spinal cord - goes to muscle
• Cross over in decussation of pyramids (medulla) for motor function of limbs

Question 24

What is the spinothalamic tract?

Answer 24

Carries pain and temperature from contralateral side of the body

Question 25

What are the dorsal columns?

Answer 25

• Carries sensory info for fine (discriminative touch)
• Fasciculus cuneatus - upper limbs
• Fasciculus gracillis - lower limbs

Question 26

How many neurones are there in the sensory pathway

Answer 26

3

Pain/temperature
• Receptor => spinal cord => thalamus => cortex

Proprioception/fine touch
• Receptor => medulla => thalamus => cortex

Question 27

Why are reflexes useful for neurological tests?

Answer 27

• Protective mechanism where brain is not needed, even though it has a huge influence
• Spinal cord injury - still should have reflex
• No reflex - probably peripheral nerve damage
• Can use patella tendon test

Question 28

What factors affect severity of spinal lesions?

Answer 28

• Loss of neural tissue
- usually small if due to trauma, degenerative disease can be more extensive
• Vertical level
- higher lesion - greater disability
- ventilator needed above C3-5
• Transverse plane

Question 29

What are the 2 stages of injury to the lateral corticospinal tract?

Answer 29

• Stage 1: spinal shock - loss of reflex activity below the lesion, lasting few days-weeks = flaccid paralysis
• Stage 2: return of reflexes - hyperreflexia, spasticity, over course of weeks/months = rigid paralysis

Question 30

What is Brown-Séquard syndrome?

Answer 30

• Unilateral lesions affecting half of the spinal cord
• Deficit to lesion depends on where the tract decussates
• Weakness/paralysis and loss of proprioception on one side (ipsilateral) of the body - (hemiparaplegia)
• Loss of pain and temperature sensation on the other side (contralateral) - (hemianesthesia)