Motor Control 2

Question 1

How is precise movement achieved by neurons in the motor cortex??

Answer 1

Instead of each neuron firing for one direction, the population of neurons fire to create a combined population vector, which determines the path of movement the skeletal muscle will create

Question 2

Is movement controlled by feed forward or feedback mechanisms?

Answer 2

Both

• A change in body position initiates rapid feedback to alter stature for stability
• When you anticipate movement brainstem nuclei can initiate feedforward anticipatory adjustments to correct posture

Question 3

When an UMN injury is sustained what happens?

Answer 3

• Initial hypoytonia “shock”: spinal circuits deprived of cortical input
• Spinal motor reflexes then return and strengthen
• Develop increased muscle tone, hyperactive stretch reflex due to removal of inhibitory influences

Fine finger movements can also be lost

Question 4

Which parts of the brain influence the basal ganglia? How does the basal ganglia select and initiate willed movement?

Answer 4

The frontal, prefrontal and parietal cortex

Basal ganglia receive movement suggestions from here, then feeds some on to area 6 via the ventral lateral nucleus in dorsal thalamus (Vlo)

Question 5

What nuclei form the input zone of the basal ganglia?

Answer 5

The corpus striatum

Caudate nucleus + putamen

Question 6

What is the corticostriatal pathway?

Answer 6

Pathway by which areas all over the cortex provide input to the corpus striatum

Multiple parallel pathways with different functions

Question 7

When do the putamen and caudate fire in relation to movements?

Answer 7

• Putamen fires before limb/trunk movements
• Caudate fires before eye movements

Both are predictive of movements

Question 8

Describe the basal ganglia motor loop (cortex-basal ganglia-cortex)

Answer 8

• Globus pallidus is constantly inhibiting VLo neurones to stop unwanted movement
• Putamen has an inhibitory effect on the globus pallidus, so putamen excitation by the cortex allows VLo to excite the SMA in the cortex, creating movement

Question 9

What is the indirect pathway with regards to the motor loop?

Answer 9

Direct pathway is the globus palladus inhibition causing movement

While this occurs, an indirect pathway also occurs via the subthalamic nucleus, it is an inhibitory pathway that suppresses competing/inappropriate movements

Basically just subthalamus excites instead of inhibits globus pallidus

Question 10

Describe the pathophysiology of parkinsons

Answer 10

• Neurones in the substantia nigra degenerate
• Less dopamine synthesized, less dopamine input to the striatum
• Causes hypokinesia

Question 11

What is hypokinesia?

Answer 11

Decreased bodily movement

• Slowness, difficulty moving, increased muscle tone (rigidity)

Question 12

Describe the pathophysiology of huntingtons disease

Answer 12

• There is profound loss of caudate, putamen and globus pallidus
• Loss of ongoing inhibitory effects of basal ganglia
• Causes characteristic chorea (abnormal involuntary movements)

Question 13

What is characteristic chorea?

Answer 13

Spontaneous, uncontrolled movements with no purpose (no intent)

Question 14

What is the function of the cerebellum with regards to movement?

Answer 14

• Determine the direction, timing and force of muscle contractions needed for precise movement

Question 15

Which tract connects the cerebellum to the rest of the movement circuit?

Answer 15

The cortico-ponto-cerebellar projection

connects cerebrum and cerebellum through pons and middle cerebellar peduncle

Question 16

Via which brain structure does the cerebellum communicate with the cortex?

Answer 16

Via the ventrolateral thalamus

Question 17

What is the effect of lesion to the cerebellum/dampening of cerebellar input via alcohol?

Answer 17

Ataxia

Uncoordinated, inaccurate movements. (eg. can’t touch nose with eyes shut)

Question 18

How do the pons and cerebellum influence the motor loop?

Answer 18

By altering VLo input on area 4 of the brain

Basal ganglia modify input to area 6 - movement planning instead of movement itself