Spinal cord function and dysfunction

Question 1

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

Answer 1

Cervical enlargement (C3-T1) 
Lumbar enlargement (L1-S3) 

They have extra neurones which innervate the muscles of the upper and lower limbs

Question 2

What anchors the spinal cord to the dura?

Answer 2

Denticulate ligament (extensions of the pia)

Question 3

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

Answer 3

Epidural space – this can be used for injecting anaesthetics (epidural anaesthesia) e.g. during natural childbirth

Question 4

Where is spinal anaesthetic injected into? When might it be used?

Answer 4

Subarachnoid space

Routine Caesarian section

Question 5

What are the major tracts of the spinal cord?

Answer 5

• Fasciculus gracilis (in dorsal column)
• Fasciculus cuneatus (between F.g. and anterior horn)
• Lateral and anterior corticospinal tracts
• Spinothalamic tract

Question 6

Briefly state the role of the dorsal column tracts

Answer 6

Sensory (fine touch, vibration, proprioception) from ipsilateral lower limb (f.g.) and upper limb (f.c.)

Question 7

Briefly state the role of the spinothalamic tract

Answer 7

Sensory (pain and temperature) from contralateral side of the body

Question 8

Describe the pathway of the corticospinal tracts

Answer 8

• A collection of axons carry motor information from the primary motor cortex, premotor cortex and supplementary motor area towards the spinal cord
• The axons converge into bundles called cerebral peduncles, and descend through the midbrain, the pons and into the medulla (as medullary pyramids)
• At the base of the pyramids, approx. 85% of fibres decussate and form the lateral corticospinal tract => terminate in ventral horn and synapse with lower motor neurones
• The other 15% of fibres will not decussate and form the anterior corticospinal tract (however most will eventually decussate in the spinal cord just before they synapse with lower motor neurones)

Question 9

What is the difference between these two tracts in terms of the control of muscle movement?

Answer 9

LCT primarily controls muscle movement in limbs

ACT is involved with movement of the muscles of the trunk

Question 10

How is the dorsal column sensory pathway different to the spinothalamnic pathway?

Answer 10

DCP: 1st order neuron travels up spinal cord in dorsal column and synapses with a 2nd order neuron in the medulla. It decussates and travels up to the thalamus where it synapse with a 3rd order neuron. 3rd order neuron => sensory cortex.

SP: 1st order neuron synapses in the dorsal horn, and then the second order decussates at the same level and ascends in the spinothalamic tract to the thalamus where is synapses with a 3rd order neuron

Question 11

Where are autonomic neuronal cell bodies found within the spinal cord?

Answer 11

Lateral horns (only thoracolumbar and sacral segments)

Question 12

What three factors affect the severity of a spinal lesion, and how?

Answer 12

Loss of neural tissue
- Small e.g. trauma, or more extensive e.g. metastases, degenerative disease

Vertical level
- Higher the lesion, greater the disability

Transverse plane
- Most lesions are not complete i.e. only affect particular tracts

Question 13

What are the two stages of lateral corticospinal tract damage?

Answer 13

Stage 1 = SPINAL SHOCK
Loss of reflex activity below the lesion, lasting for days or weeks resulting in flaccid paralysis

Stage 2 = RETURN OF REFLEXES
Hyperreflexia and/or spasticity (intense reflexes) resulting in rigid paralysis

Question 14

Where do pain and temperature first order neurones synapse in the dorsal horn?

Answer 14

Substantia Gelatinosa

Question 15

What is the filum terminale?

Answer 15

An extension of the pia mater that is attached to the coccygeal segments, whose function is to suspend the cord in the CSF