L13 - Upper motor neurons

Question 1

Lateral white matter in the spinal cord have axons from the ____, medial white matter in the spinal cord have axons from the ____.

Answer 1

Motor cortex, brainstem

Question 2

3 descending projections from the brainstem to the spinal cord and what they do

Answer 2

1) Lateral and medial vestibulospinal tracts - operates via hair cells detecting gravity related changes, helps maintain balance
2) Reticulospinal tract - It is an extrapyramidal motor tract that descends from the reticular formation in two tracts to act on the motor neurons supplying the trunk and proximal limb muscles. It is involved mainly in locomotion (programmatic complex movements) and postural control.
3) Colliculospinal tract - most rostral part of brainstem, nerve pathway that coordinates head and eye movements, mediating reflex postural movements of the head in response to visual and auditory stimuli. It is responsible for motor impulses that arise from one side of the midbrain to muscles on the opposite side of the body.

Question 3

What pathway is the medial lemniscus involved in

Answer 3

Somatosensory

Question 4

EXP: Subject told to pull on bar if he hears a tone. What muscles are involved? Which one activates first?

Answer 4

Biceps pulling bar and calves tense in anticipation of using biceps. The calves are a preemptive postural control and hence activates 100 ms before biceps.

Question 5

What is another name for the brainstem?

Answer 5

Corticalbulbar

Question 6

There is another type of corticalbulbar neuron activating motor neurons in brainstem controlling ___ muscles.

Answer 6

Facial

Question 7

T/F: Premotor is complicated and often bilateral, needing more stimulation to elicit response

Answer 7

True

Question 8

T/F: Stimulating surface of brain elicted strong contralateral movements from primary area

Answer 8

True

Question 9

Betz cells are giant pyramidal cells found in ____, whats special about their size?

Answer 9

Primary motor cortex. Largest neurons in NS (30-40 microns in soma)

Question 10

Majority of neurons in NS is ____ and spinal cord injury leads to spinal cord being more easily ____

Answer 10

Inhibitory, excitable

Question 11

Why does pyramidal decussation (fibres cross over) occur?

Answer 11

Caudal medulla

Question 12

Mirror motor neuron activity in a ventral-anterior sector of the lateral premotor cortex experiement

Answer 12

1) Neuron fires when doing action as well as watching someone else do it
2) Same task but with pilers - no response from watching this scenario
2) Covering up target - monkey still reaches and grab, neurons still fire

CONCLUSION: Motor neuron that is also activated by seeing someone else do it

Question 13

Babinski sign

Answer 13

It is a form of clinical diagnosis of damage to the motor system. Extensor plantar response and fanning of toes when pen runs up soles of feet, opposed to normal response of toes down (flexion). Infantile form of this reflex must have been suppressed by brain and once suppression is removed by spinal injury, the response returns.