Exam 2

What are central pattern generators (CPGs)?

Neural circuits that produce rhythmic outputs like walking or breathing without rhythmic sensory or descending inputs.

Where are CPGs located, and how do they contribute to motor control?

Found in the spinal cord and brainstem; they generate autonomous motor patterns and can function without sensory feedback.

What is fictive locomotion?

Motor patterns recorded without actual movement, showing that rhythmic motor patterns are centrally generated.

What is the half-center model of locomotion?

Two groups of neurons inhibit each other to produce alternating rhythmic activity.

How can sensory feedback influence CPGs?

It can reset/modulate rhythm, prolong movement phases, and aid phase transitions.

What is the function of the neuromuscular junction (NMJ)?

Synapse between motor neuron and muscle fiber where ACh causes contraction.

What happens at the NMJ during muscle contraction?

AP → Ca²⁺ influx → ACh release → Na⁺ influx in muscle → depolarization → contraction.

What is myasthenia gravis and how does it affect the NMJ?

Autoimmune attack on ACh receptors → impaired transmission → muscle weakness.

What is the difference between upper and lower motor neurons?

Upper motor neurons originate in brain/cortex; lower motor neurons directly innervate muscles.

What is the size principle in motor unit recruitment?

Smaller units are recruited first due to higher excitability; larger units follow as force demand increases.

How does reciprocal inhibition work in motor control?

Contracting muscle inhibits its antagonist via interneurons to allow smooth movement.

What role do gamma motor neurons play in muscle contraction?

Adjust muscle spindle sensitivity by contracting intrafusal fibers during movement.

What is the stretch reflex and what components are involved?

Muscle stretch activates spindle afferents → excites alpha motor neurons → contraction.

What are Renshaw cells and how do they function?

Inhibitory interneurons providing negative feedback to alpha motor neurons.

What is a motor unit and how is it organized?

A single alpha motor neuron and all muscle fibers it innervates.

How do fast and slow muscle fibers differ?

Fast: quick, fatigues fast. Slow: slower, resistant to fatigue, used for endurance.

What is the Golgi tendon organ (GTO) reflex?

Detects tension and inhibits same muscle's motor neurons to prevent damage.

What is the difference between muscle spindle and GTO function?

Spindle: stretch detection/length. GTO: tension detection/force.

What is the function of the supplementary motor area (SMA)?

Plans and initiates internally generated movement and sequences.

What is the function of the premotor cortex?

Plans/selects movements in response to external cues.

How does the cerebellum contribute to motor control?

Compares intended vs actual movement, adjusts for coordination and precision.

What happens when the cerebellum is damaged?

Ataxia, intention tremor, dysmetria, and poor coordination.

What is the basal ganglia’s role in motor control?

Initiates desired movement and inhibits unwanted ones through direct/indirect pathways.

What is the difference between the direct and indirect pathways in the basal ganglia?

Direct: facilitates movement (disinhibits thalamus); Indirect: inhibits movement (more inhibition of thalamus).

What is Parkinson’s disease and how does it affect motor control?

Degeneration of substantia nigra dopamine neurons → decreased direct pathway activity → motor symptoms like bradykinesia, tremors.