L15: Control of Movement

Question 1

What do Central Pattern Generators (CPGs) control?

Answer 1

• control some simple repetitive behaviours
• repetative motions, don’t have to think about it
• recieve imput from higher brain regions → voluntary override

Question 2

Describe the activity pattern of CPGs

Answer 2

• neurons fire in bursting pattern
  
  • e.g. two cells inhibit each other, creates oscillatory pattern of contraction, e.g. extensor/flexor muscles

Question 3

Describe the motor control hierarchy

Answer 3

planning in PFC -> motor cortex -> descending pathways -> motor neurons activate skeletal muscle -> proprioceptive info back to brain to modify and control movement

Question 4

Describe the role of the basal nuclei in movement control

Answer 4

basal nuclei adjust movement by:
1. alter sensitivity of pyramidal cells to adjust output along corticospinal tract
2. change the excitatory or inhibitory output of medial and lateral pathways

Question 5

Describe the Somatotopic organization of Primary Motor Cortex

Answer 5

• homunculus
• lower limb medially -> upper limb -> face -> tongue

Question 6

What are 3 descending pathways

Answer 6

• Lateral corticospinal tract
• Ventral corticospinal tract
• Brainstem pathways

Question 7

Describe the Lateral corticospinal tract

Answer 7

motor cortex controls fine movement -> medulla -> cross the midline and descend as lateral
corticospinal tract (LCST) -> terminate on interneurons -> motorneurons located laterally in spinal cord grey matter

Question 8

Describe the Ventral corticospinal tract

Answer 8

motor cortex controls course movement (neck, trunk, shoulders etc.) -> medulla -> doesn’t cross the midline but descends on same side as ventral corticospinal tract (VCST) -> motorneurons located medially in spinal cord grey matter

Question 9

Describe the Brainstem pathways

Answer 9

• Co-ordinates activity in large axial & proximal muscle groups (posture, locomotion) & routine activities
• motor neurons located medially in spinal cord grey matter -> to body wall muscles

Question 10

What is the role of the cerebellum in movement control?

Answer 10

• Organises timing of muscle contractions
• Compares planned movement with
  actual result, modifies ongoing activity to
  make movements smooth and accurate

Question 11

What disorders happen when loss of function in the cerebellum?

Answer 11

slow, uncoordinated movements = ataxia
* “Drunken gait”-sway and stagger when walking
* Dysmetria – inability to judge distances and stopping points
* Tremors – eg “essential tremor”
* Muscular weakness (hypotonia)
* Slurred speech (ataxic dysarthria)
* Abnormal eye movements (nystagmus)

Question 12

What is the role of the basal ganglia/nuclei in movement control?

Answer 12

• planning, initiating and monitoring of
  movements
• form processing loops
  
  • cortex to basal ganglia to thalamus then back to cortex

Question 13

Differentiate between the two pathways of the basal ganglia

Answer 13

• direct pathway = small amount of inhibition = big amount of activity back to cortex
• indirect = more structures involved = lots of inhibition of thalamus = less activity back to cortex

Question 14

outline the role of dopamine in basal ganglia pathways

Answer 14

all these pathways controlled by dopamine
- promotes movement by activated direct pathway
- inhibits in indirect pathway

Question 15

What happens in Parkinson’s disease, and how is it treated

Answer 15

Death of substantia nigra neurons -> reduces dopamine output ->
in inability to initiate movements, slowed movements (Bradykinesia),
stiffness, and tremor
* Typically results in decrease in activity of direct pathway, and increases activity in indirect pathway
* treatment with dopamine precursors (Levadopa) or DBS