Session 5

Question 1

Where are upper and lower motor neurones found?

Answer 1

Upper - cell bodies in precentral gyrus
Lower - cell bodies in CNS (ventral horns and cranial nerve nuclei - some CNS lesions have lower motor neurone signs) but amjority of nerve in PNS

Question 2

What are the signs of lower motor nerve lesions?

Answer 2

Weakness, wasting (after few weeks due to reduced growth factors), a/hypo-reflexia, hypotonia, fasciculations (uncoordinated contraction), fibrillation

Question 3

What stops the hamstrings from resisting the knee jerk during a patella tendon reflex?

Answer 3

There are collateral branches of the sensory neurones that descend down the ventral horns from L3 to L5 to inhibitory interneurones to inhibit the lower motor neurones

Question 4

What is the net effect of UMNs on LMNs?

Answer 4

Inhibitory via inhibitory interneurones

Question 5

Where is the internal capsule found on coronal section?

Answer 5

Between the thalamus and lentiform nucleus

Question 6

What are the 3 parts of the internal capsule and what neurones do they carry?

Answer 6

Anterior limb
Posterior limb - arm, trunk, leg going along
Genu (knee) - contains UMN supplying the face

Question 7

How do motor fibres enter the midbrain from the internal capsule?

Answer 7

Into the cerebral peduncles (mickey mouse’s ears) then into the pyramids in the medulla

Question 8

Where do motor fibres deccusate in the CNS and what do they form?

Answer 8

In the deccusation of the pyramids (in medulla) to form the lateral corticospinal tracts

Question 9

What is the function of the tectospinal tracts?

Answer 9

Reflex actions in response to visual and auditory stimuli

Question 10

What is the function of vestibulospinal tracts?

Answer 10

Responsible for upright posture and head stabilization. Receives input from the vestibulocochlear nerve. Think chickens!

Question 11

What is the function of the reticulospinal tract?

Answer 11

Regulates muscle tone

Question 12

What are the upper motor neurone signs?

Answer 12

Weakness
Hypertonia; spasticity (arms flexed and legs exended due to more powerful muscles with increased tone) and clasp knife reflex (rapid reducion in resistance when flexing a joint)
Hyperreflexia
Extensor plantar reflex
All due to lost inhibition leading to hyperactivity of the reflex arcs. Initially there is flaccid paralysis due to spinal shock.