6. Motor System

Question 1

Where are the nuclei of the upper motor neurone and lower motor neurone of the motor system found?

Answer 1

Upper motor neurone - primary motor cortex of CNS.

Lower motor neurone - ventral horn of spinal cord or in the brainstem motor nuclei of the PNS.

Question 2

A lesion where can destroy upper motor neurones?

Answer 2

A CNS lesion.

Question 3

A lesion where can destroy lower motor neurones?

Answer 3

A CNS and a PNS lesion.

Question 4

What are the signs of lower motor neurone damage?

Answer 4

Weakness.
Areflexia.
Muscle wasting.
Fasciculation.
Hypotonia.

Question 5

What is the net effect of upper motor neurones on lower motor neurones?

Answer 5

Inhibitory.

Question 6

What is the main role of the lateral corticospinal tract?

Answer 6

Dexterity, hand movements and general muscle control (not so much for general posture).

Question 7

In a stroke why are only the muscles on one side of the lower half of the face affected?

Answer 7

Upper half of the face is bilaterally innervated by CNVII, the lower half is only innervated by the contralateral side.

Question 8

What is the babinskri reflex?

Answer 8

Stimulation of the plantar foot causes dorsiflexion of the large toe.

Question 9

What signed are seen in damage to upper motor neurones? Which of these are late signs eg in a stroke?

Answer 9

Weakness.
Hypertension - late sign.
Hyperreflexia - late sign.
Extensor plantar reflex - late sign.

Question 10

What happens immediately after damage to the upper motor neurones in a stroke?

Answer 10

Spinal shock - stroke destroys the upper motor neurons, lower motor neurone got into spinal shock and their activity levels decrease initially leading to weakness, hypotonia, areflexia and flexor plantar reflex. Then over time the activity of the lower motor neurones increase and then go into overdrive causing the classic upper moor neurone signs.