Motor control 2

Question 1

What is meant by directional tuning?

Answer 1

Commands to perform precise movements are encoded in the integrated activity of large numbers of neurones in M1 (primary motor cortex)

If you imagine a precise movement which has several directions (vectors) it could go in - each neuron associated with the movement has its own preferred direction

If we decide to move in one direction, the neurones corresponding to that movement go fkn mental whereas the other direction’s neurones stay pretty chill

Question 2

Shown below are the action potentials of a single neuron as a monkey moves a joystick in various directions

What does the diagram show?

Answer 2

Activity increased before movements in yellow zone and decreased for movements in purple zone

This means the direction associated with that neuron (its preferred direction) is the ones in yellow - as activity increases before those movements

Question 3

What is the importance of feedback mechanisms to us maintaining balance/position?

Answer 3

A change in body position initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurones

The movements initiated correct postural instability

Question 4

What is the importance of feedforward mechanisms in maintaining posture?

Answer 4

Before movements begin, brainstem reticular formation nuclei (controlled by the cortex) initiate feedforward anticipatory adjustments to stabilize posture

Question 5

What are the signs of cortical damage (specifically damage to descending motor pathways)?

Answer 5

Damage to Desc. pathways will cause ‘Upper motor neuron syndrome’ - however specific signs are specific to the area damaged

Spinal shock:

• Immediate flaccidity of contralateral muscles - hypotonia
• After a few days - spinal motor reflexes begin to return

Plantar reflex:

• UMN damage will cause plantar extension (should be flexion)
  
  • Note - in babies, plantar extension is normal
• Due to incomplete upper control of spinal circuits

Spasticity:

• hypertonia, hyperactive stretch reflex, clonus
• develops after recovery from spinal shock^ - basically overcompensated

Loss of fine finger movements