Primary motor cortex and descending pathways

Question 1

primary” motor cortex

Answer 1

Outputs (upper motor neurons) neurons project down corticospinal tract
responsible for generating the neural impulses controlling execution of movement
-only active when executing movements
-lowest electrical thresholds for stimulating movement.
-cortical inputs from area 6 and somatosensory areas 1,2,3.
Stimulation leads to simple movements.

Question 2

Brodmann Area 6 - premotor and supplementary motor areas

Answer 2

• PMA: sensory guided movements, control of proximal and trunk muscles
• SMA: two subdivisions – caudal SMA proper, rostral pre-SMA
• SMA proper - planning of motor actions, especially those guided from memory
• pre-SMA: acquiring new motor sequences
• Electrical stimulation leads to complex movements.

Question 3

lesion of premotor and supplementary motor areas

Answer 3

-lesions cause apraxia – impairment of complex but not simple movements.

Question 4

Key difference between PMA and SMA:

Answer 4

• premotor area incorporates sensory info;
• SMA is for internally generated movements.
• SMA: performing an already-learned sequence (retrieval), or linking multiple, known sequences.

Question 5

in simple finger tip flexion which area is involved?

Answer 5

primary motor cortex and primary somatosensory

Question 6

sequential finger movement

in Mental rehearsal of finger movements

Answer 6

primary motor cortex and primary somatosensory
and SMA

Mental rehearsal of finger movements only SMA

Question 7

CAN brain areas controlling movement be engaged without performing the movement?

Answer 7

In 2006, Owen and colleagues were able to detect activity in the supplementary motor area of a patient who had been in a persistent vegetative state for about 5 months following a car accident. Prior to the accident, the woman had been a tennis player, and the activity they recorded was consistent with activity in the brains of control subjects asked to imagine playing tennis. This again demonstrates that the brain areas controlling movement can be engaged without actually performing the movement.

Question 8

Difference in neuron of primary motor area, premotor area and supplementary motor areas

Answer 8

Neurons in the:
•primary motor area can directly control movement (via projections to LMN)
•premotor areas use sensory information to link the motor cortex and outside world. Their activity codes the goal to be accomplished, not the muscle contractions
•supplementary motor areas are involved in the motor plan - specifying and learning sequences of muscle contractions necessary to accomplish a complex movement.

Question 9

How are long and complex movements co-ordinated if the environment is changing?

Answer 9

=> Need to integrate sensory feedback and awareness of body position into a closed loop system

Question 10

Cerebellum helps coordinate ….

Answer 10

sequences of muscle contractions.

• adjusts posture and gait
• refines movements in progress (evaluates disparities between intention and action)
• adapts & improves repetitions of the same movement (trial and error)