Spinal Control of Movement

A comprehensive set of flashcards covering spinal motor control, motor unit classification, proprioceptors, spinal reflexes, and the mechanisms of locomotion.

Lower Motor Neurons

Neurons that provide the direct connection between the nervous system and skeletal muscle, serving as the final pathway through which neural signals produce movement.

Upper Motor Neurons

Neurons that do not directly contact skeletal muscle but influence lower motor neurons through descending pathways originating within the brain.

Motor Neuron Pools

Structures containing groups of motor neurons that control a particular muscle, often organized longitudinally through the spinal cord.

Alpha Motor Neurons

Lower motor neurons that directly innervate the force-generating muscles responsible for contraction and movement.

Gamma Motor Neurons

Neurons that innervate specialized sensory structures known as muscle spindles to maintain sensitivity through both muscle contraction and relaxation.

Feed Forward Control

A control strategy relying on predictions generated before movement begins, issuing commands based on prior experience and expected outcomes.

Feedback Control

A control strategy that depends on sensory information generated during motion to allow ongoing corrections and adjustments.

Motor Unit

A structure consisting of a single alpha motor neuron and all of the muscle fibers that it innervates.

Slow (Type I) Motor Units

Motor units that generate low levels of force and contract slowly, but are highly resistant to fatigue.

Fast Fatigue-Resistant Motor Units

Motor units that generate greater force and contract rapidly, capable of sustaining activity longer than fast fatigable units.

Fast Fatigable Motor Units

Motor units that produce the greatest force and fastest contractions, typically reserved for short-duration high-power movements like sprinting.

Size Principle

The principle stating that motor units are recruited in a highly predictable order from small, slow motor units to larger, fast motor units as force demands increase.

Proprioception

The sensory system that allows the nervous system to continuously monitor the position and movement of the body.

Muscle Spindles

Encapsulated sensory organs located within skeletal muscle that detect changes in muscle length.

Intrafusal Muscle Fibers

The $8$ to $10$ specialized fibers within a muscle spindle that function as sensory receptors rather than force-producing structures.

Nuclear Bag Fibers

Intrafusal fibers with nuclei clustered in a central region that are particularly sensitive to the rate of muscle stretch.

Nuclear Chain Fibers

Intrafusal fibers with nuclei arranged in a linear sequence that provide information about sustained muscle length.

Group IA Afferents

Large diameter sensory axons forming primary endings around bag and chain fibers that are highly sensitive to dynamic changes in muscle structure.

Group II Afferents

Secondary sensory endings providing information about static muscle length.

Stretch Reflex

A monosynaptic excitatory response where stretching a muscle activates muscle spindles, causing an immediate contraction of that same muscle.

Reciprocal Inhibition

The process of activating one muscle group while simultaneously suppressing alpha motor neurons that innervate the antagonizing muscle.

Golgi Tendon Organs

Proprioceptive receptors located at the junction between muscle and tendon that monitor the force or tension generated by muscle contraction.

Inverse Myotactic Reflex

A reflex pathway initiated by Golgi tendon organs that produces inhibition of alpha motor neurons to reduce muscle contraction in response to excessive force.

Flexion (Withdrawal) Reflex

A rapid, stereotypical response initiated by nociceptors to withdraw a limb from potentially damaging stimuli.

Crossed Extensor Reflex

A reflex coordinated with the flexion reflex where the contralateral limb becomes rigid and supportive to maintain balance as the affected limb withdraws.

Central Pattern Generators (CPGs)

Neural networks within the spinal cord that produce the timing and coordination necessary for rhythmic motion like walking or running.

Swing Phase

The phase of locomotion where the limb is lifted from the ground and advanced forward.

Stance Phase

The phase of locomotion where the limb contacts the ground, supports body weight, and contributes to propulsion.

Mesencephalic Locomotor Region

A brainstem area that can initiate locomotion by providing excitatory drive to spinal locomotor circuits through the medullary reticular formation.

Posterior Parietal Cortex

A brain region that integrates visual information with proprioceptive input to link limb position with the environment and guide movement in space.