Motor Nervous System and Pathways

Vocabulary flashcards reviewing concepts of motor neurons, classes of movement, structural hierarchy, and descending motor pathways based on the lecture notes.

Peripheral Motor Neurons (MNs)

Motor neurons located in the ventral horn of the spinal cord and the brainstem.

Motor Neuron Pool

A collection of motor neurons that innervate a single muscle, such as the triceps.

Motor Unit

The basic functional unit of motor control, consisting of a single motor neuron and all the muscle fibers it innervates.

Trophic Effect

The vital nutritional and maintenance effect exerted by motor neurons on muscle fibers beyond initiating contraction.

Reflex Responses

Stereotyped, involuntary movements initiated by a specific stimulus.

Rhythmic, Repetitive Motions

Sequences of relatively stereotyped and almost automatic voluntary movements, such as walking.

Voluntary Movement

Purposeful, goal-directed, complex, and learned movements.

Spinal Level (Motor Control)

The hierarchical level responsible for local patterns of movement, such as programmed withdrawal reflexes and basic rhythmic motions.

Midbrain/Brainstem Level (Motor Control)

The hierarchical level that focuses on maintaining axial tone for standing and continuous modification of muscle tone to maintain equilibrium and balance.

Highest (Cortical) Level (Motor Control)

The hierarchical level including the association cortex and motor areas that selects the movement goal and strategy.

a-Motor Neurons

The most numerous type of spinal motor neurons, which innervate extrafusal muscle fibers to produce actual muscle contraction.

Gamma Motor Neurons

Spinal motor neurons that innervate intrafusal muscle fibers within the muscle spindle to keep them taut and capable of detecting changes in muscle length during contraction.

Proximal-Distal Rule

An arrangement rule stating that motor neurons for proximal (trunk) muscles are located medially in the ventral horn, while motor neurons for distal (limb) muscles are located laterally.

Extensor-Flexor Rule

An arrangement rule stating that motor neurons for flexor muscles are located dorsally, while motor neurons for extensor muscles are located ventrally within the horn.

Propriospinal Neurons

Intrinsic spinal cord neurons whose axons terminate within its boundaries, functioning in sensorimotor integration, coordination between agonists and antagonists, and regulation of motor acts.

Medial Line (Cranial Nerves)

A brainstem organizational line located close to the midline that contains motor efferent nuclei.

Lateral Line (Cranial Nerves)

A brainstem organizational line formed by the special visceral motor column.

Ventromedial System

A motor control system descending in the ventral column that terminates in the ventromedial motor neuron pool to control posture, balance, and axial/proximal limb muscles.

Ventromedial System Pathways

A group of tracts comprising the Vestibulospinal, Reticulospinal, Tectospinal, and Anterior (Ventral) corticospinal tracts.

Dorsolateral System

A motor system with crossed axons descending in the lateral column that terminates in the dorsolateral motor neuron pool to control skilled, fractionated movements of distal limb segments.

Dorsolateral System Pathways

A group of tracts comprising the Lateral corticospinal, Corticobulbar, and Rubrospinal tracts.

Lateral Corticospinal Tract

A dorsolateral pathway originating in the primary motor cortex that is the only descending pathway with direct monosynaptic innervation on alpha motor neurons.

Rubrospinal Tract

A dorsolateral system pathway originating in the red nucleus of the brainstem.