15: Control of movement

Question 1

What features are the spinal cord involved in? (3)

Answer 1

• Processing commands from brain and giving motor output. - Has specific circuitry to allow to it run autonomously.

• Reflexes
- Stretch (muscle spindle) reflex
Can be easily generated by tapping into the patella region
- Tension (Golgi tendon organ) reflex

• Rhythmic motor patterns
- E.g. locomotion, chewing

Question 2

Describe the stretch reflex

Answer 2

slides

• Contraction of extensor muscles (up)
• Relaxation of flexor muscles (down)
• Information about muscle length sent to brain

(maintains length)

Question 3

Describe the tension reflex

Answer 3

Maintains force

• Inhibition of the motor neuron of the extensor muscle and its synergist
• Excitation of flexor muscles’ and motor neuron

Slides

Question 4

Describe the withdrawal reflex

Answer 4

Slides

• Ipsilateral flexor muscle’s motor neuron is stimulated (withdrawal reflex). Flexors active, extensors relaxed
• Opposite limb is extended (cross-extensor reflex) to support. Extensor active, flexor relaxed

Question 5

Describe somatotopy in primary motor cortex

Answer 5

slides

Question 6

Describe the corticospinal pathway

Answer 6

Output from motor cortex controls spinal neurons, or fine, isolated movements (crosses to opposite side).

Note: most input is to interneurons

Question 7

Describe the brainstem pathway

Answer 7

Coordinated activity in large muscle groups, for posture, locomotion, routine activities (crosses and uncrossed)

Question 8

What are the special roles of primary motor cortex? (3)

Answer 8

• Special role in controlling force of muscle contractions
- Greater rate of neuronal activity, greater force

• Special role in controlling direction of movements
- Relative activity of many cortical neurons, controlling muscles each side of a joint, control the direction of movement

* Most axons from motor cortex synapse on interneurons, not α-motor neurons
* Special role of motor cortex neurons which synapse direction on α-motor neurons

- Have a particularly direct, fast and powerful effect
- Mostly for control of distal limb (hand and fingers)
- More developed in higher primates

Question 9

What are the roles of basal ganglia?

Answer 9

• Basal ganglia monitors and helps plan cortical activity involved in movement
• Helps cortex select combinations/sequences of muscle activation
• Cycle through loop (cortex -basal ganglia -cortex) occurs several times during preparation for movement
• Positive feedback to cortex for selected pathways
• Needed for initiation of movements
• Dopamine input [from substantia nigra] vital to allow proper functioning
- Death of dopamine neurons produces Parkinson’s disease

Question 10

What are the roles of the cerebellum?

Answer 10

Helps plan, execute, and learn motor programs

slides

Question 11

What are results of cerebellar injury? (9)

Answer 11

1. Loss of coordination of motor movement (asynergia)
2. The inability to judge distance and when to stop (dysmetria)
3. The inability to perform rapid alternating movements (adiadochokinesia)
4. Movement tremors (intention tremor)
5. Staggering, wide based walking (ataxic gait)
6. Tendency toward falling
7. weak muscles (hypotonia)
8. Slurred speech (ataxic dysarthria)
9. Abnormal eye movements (nystagmus)