Lecture #15 - Motor Systems

Q: What are the four basic neural subsystems that control movement?

A: (1) Descending pathways from motor cortex/brainstem, (2) Cerebellum, (3) Basal ganglia, (4) Local spinal cord circuitry.

Q: Which cortical areas are involved in voluntary movement control?

A: Primary motor cortex, premotor cortex, supplementary motor area, parietal motor area, prefrontal cortex.

Q: What is the function of the primary motor cortex?

A: Executes specific, well-defined motor movements via upper motor neurons.

Q: What is the function of the premotor cortex?

A: Plans complex motor responses, transfers plans to primary motor cortex.

Q: What is the function of the supplementary motor area?

A: Programs motor sequences, mental rehearsal, coordinates bilateral movements.

Q: What is the function of the parietal motor area?

A: Correlates sensory information with body position; helps initiate movement based on motivation.

Q: What is the function of the prefrontal cortex in movement?

A: Plans, goals, and intentions for future actions.

Q: What is the overall role of the cerebellum in movement?

A: Unconscious level control; compares intended and actual movement; midcourse corrections.

Q: What are the three functional divisions of the cerebellum and their roles?

A: Spinocerebellum: compares intended vs. actual movement,
Cerebrocerebellum: plans/programs movements,
Vestibulocerebellum: balance and eye movements.

Q: What is the primary function of the basal ganglia in movement?

A: Plans voluntary movement; controls speed and size of movement.

Q: Do the basal ganglia connect directly with the spinal cord?

A: No, they regulate movement via connections with the motor cortex.

Q: What are alpha (α) motor neurons?

A: Neurons that innervate extrafusal muscle fibers to generate force.

Q: What are gamma (γ) motor neurons?

A: Neurons that innervate intrafusal muscle fibers in muscle spindles to maintain spindle tension.

Q: What is a motor unit?

A: An alpha-motor neuron and all the extrafusal muscle fibers it innervates.

Q: What structure monitors muscle length?

A: Muscle spindles (stretch receptors).

Q: What structure monitors muscle tension?

A: Golgi tendon organs.

Q: What is alpha-gamma coactivation?

A: Simultaneous contraction of intrafusal fibers by γ-motor neurons during extrafusal contraction to maintain spindle sensitivity.

Q: What are spinal reflexes?

A: Stereotypical motor responses to specific stimuli involving a reflex arc.

Q: What is the stretch (myotatic) reflex?

A: Monosynaptic reflex where muscle stretch activates α-motor neurons to contract the same muscle.

Q: What is the Golgi tendon reflex?

A: Disynaptic reflex where high tension activates Golgi tendon organs causing relaxation of the contracting muscle.

Q: What is the flexor withdrawal reflex?

A: Polysynaptic reflex withdrawing a limb from painful stimulus while extending the contralateral limb for support.