Structure and function of the spinal cord part 2

Question 1

What can damage to anteriolateral column as a result of a lesion on one side of spinal cord cause

Answer 1

• Loss of pain, temperature and crude touch on opposite side

Question 2

What does outside compression of cord and therefore damage to anterolateral column cause

Answer 2

• Loss of lower limb pain first(fibres sit laterally)

Question 3

What can an inside grey matter tumour affecting the anterolateral column cause

Answer 3

• Loss of upper limb pain first(fibres sit medially)

Question 4

What do the spinocerebellar tracts detect

Answer 4

• Unconscious muscle proprioception(from muscle spindles, golgi tendon organs)
• For smooth motor coordination

Question 5

What do the spinocerebellar tracts consist of

Answer 5

• Two neurons only(only 1st order and 2nd order)

- Four tracts

Question 6

Do the fibres of the spinocerebellar tracts cross

Answer 6

• No they remain uncrossed(note that second order neurons of anterior tract cross to other side and then cross back)
• Left cerebellum controls left side of the body

Question 7

Path of first-order neurons in the spinocerebellar tracts

Answer 7

• Synapse in dorsal horn

Question 8

Path of second-order neurons in the spinocerebellar tracts

Answer 8

• Ascend in lateral column to cerebellum

- Very fast axons

Question 9

What is the effect of a lesion on one side of spinal cord affecting the spinocerebellar tracts

Answer 9

• Uncoordinated lower limb muscular activity on same side

- Although rarely damaged in isolation(other tracts are normally affected)

Question 10

What is the corticospinal tract responsible for

Answer 10

• Great voluntary motor pathway

Question 11

What type of neurons does the corticospinal tract contain

Answer 11

1. Upper motor(premotor) neuron - from cerebral cortex to ventral horn
2. Lower motor neuron - From ventral horn to skeletal muscle

Question 12

Path of pyramidal tract joining primary motor cortex to the lateral/anterior corticospinal tract

Answer 12

Primary motor cortex –> posterior limb on internal capsule –> cerebral peduncle –> pons –> pyramids of medulla –> lateral/anterior corticospinal tract

Question 13

Where do the fibres of the corticospinal tract cross

Answer 13

• Cross at the pyramids of decussation
• 80% cross - lateral corticospinal tract
• 20% on same side - anterior corticospinal tract

Question 14

What happens to the fibres of the anterior corticospinal tract

Answer 14

• Supply deep neck muscles and cross in spinal cord

Question 15

Topographical organisation of fibres of the corticospinal tract in ventral horn

Answer 15

• Medial - trunk
• Anterolateral - Proximal limb segments
• Posterolateral - distal limb segments
  segments - muscles

Question 16

How does motor neuron disease occur

Answer 16

• Disruption of the corticospinal tract

Question 17

How does upper motor neuron disease occur

Answer 17

• Degeneration of upper motor neurons
• Spastic paralysis(increased muscle tone)
• Overactive tendon reflexes
• No significant muscle atrophy

Question 18

How does localisation of loss of axons affect each side in upper motor neuron disease

Answer 18

• Loss of axons above pyramids will result in effects on the opposite side as will cross over
• Loss of axons below pyramids result in effects on the same side

Question 19

How does lower motor neuron disease occur

Answer 19

• Degeneration of lower motor neurons in ventral horn
• Flaccid paralysis(no muscle tone)
• Muscle atrophy

Question 20

Defects in what gene causes spinal muscular atrophy

Answer 20

• Caused by defects in the SMN1 gene

- SMN1 gene is vital for survival of motor neurons

Question 21

What is amyotrophic lateral sclerosis

Answer 21

• Selectively affects lower and upper motor neurons

- Progressive muscle weakness and atrophy but mind intact

Question 22

Prognosis of amyotrophic lateral sclerosis

Answer 22

• Symptoms initially in limbs or bulbar signs(speech and swallowing difficulties)
• Spasticity present when upper motor neurons affected
• Short life span(-5 years - due to respiratory failure)

Question 23

What gene has been identified that has a link with development of amyotrophic lateral sclerosis

Answer 23

• eg SOD1 gene

Question 24

What are extrapyramidal tracts

Answer 24

• Do not pass through the pyramids

- Descending tracts from basal ganglia, cerebellum and pons

Question 25

What is the reticulospinal tract

Answer 25

• From reticular formation(pons) to spinal cord
• Regulates ventral horn motor activity/reflexes
• Facilitates and inhibits lower motor neurons
• Important for posture and locomotion