Motor Pathways (Chapter 14)

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Vocabulary flashcards covering key terms and definitions from the lecture notes on Motor Pathways.

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32 Terms

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Lower motor neurons

Originate in the ventral horns of the spinal cord; axons exit via ventral roots; innervate skeletal muscles; organized somatotopically.

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Alpha (a) motor neurons

Innervate extrafusal muscle fibers; part of a motor unit; drive actual muscle contraction.

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Gamma (γ) motor neurons

Innervate intrafusal muscle fibers within muscle spindles; regulate spindle sensitivity; contract only marginally.

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Motor unit

One α-motor neuron and all of the skeletal muscle fibers it innervates; size can be large or small.

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Interneurons

Provide communication between neurons; relay impulses to multiple CNS areas and help synchronize complex motor pathways.

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Motor cortex

Region where α-motor neurons originate; controls voluntary skeletal muscle movement; most neurons decussate before synapsing with LMNs.

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Betz cells

Large pyramidal neurons in Layer V of the primary motor cortex.

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Homunculus (somatotopy)

Map of the body on the motor cortex showing which cortical areas control different body parts.

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Premotor cortex

Works with primary motor cortex; plans responses to visual/sound cues; stores motor memory and context.

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Supplementary motor area

Assists motor cortex; coordinates complex or sequential movements; involved in bilateral movements and planning strength, distance, direction.

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Association cortex

Located in the prefrontal and posterior parietal regions; modulates motor movements initiated in the motor cortex.

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Basal nuclei (basal ganglia)

Modulate and modify motor impulses; include caudate nucleus, putamen, globus pallidus, subthalamic nucleus, substantia nigra; interact with thalamus via glutamate and GABA.

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Thalamus (motor role)

Receives basal ganglia input and provides excitatory feedback to the motor cortex to help regulate movement.

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Cerebellum

Modulates motor impulses for precision and accuracy; Purkinje cells output; mossy fibers bring in information; communicates with vestibular nuclei, red nucleus, and motor cortex.

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Direct (pyramidal) tracts

Voluntary motor pathways; direct cortex-to-spinal cord/brainstem connections; include corticobulbar and corticospinal tracts.

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Indirect (extrapyramidal) tracts

Involuntary motor pathways that modulate muscle tone and balance; originate in the brainstem and project to the spinal cord.

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Corticobulbar tracts

Control skeletal muscles of chewing, facial expression, tongue movement, and swallowing; synapse with brainstem cranial nerve nuclei.

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Corticospinal tracts

Carry voluntary motor commands from the motor cortex to the spinal cord; include lateral (decussates in medulla) and ventral/anterior (axial muscles, may not decussate).

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Lateral corticospinal tract

Decussates at the pyramids of the medulla; mainly innervates appendicular (limb) muscles.

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Ventral (anterior) corticospinal tract

Does not decussate at the medulla; innervates axial (trunk) muscles; some fibers may cross at spinal level.

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Vestibulospinal tracts

Indirect tracts that control balance and posture; lateral (from lateral vestibular nuclei) and medial (from medial vestibular nuclei).

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Reticulospinal tracts

Indirect tracts that control axial/postural muscles and locomotion; medial (pontine) facilitates extensors; lateral (medullary) inhibits extensors.

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Rubrospinal tract

Originates in the red nucleus; mainly influences flexor muscles in humans; decussates and runs with lateral corticospinal tract.

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Tectospinal tract

Indirect tract that coordinates head movements in response to visual stimuli; originates in the superior colliculus; largely ipsilateral or contralateral depending on level.

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Central pattern generator (CPG)

Network of neurons generating rhythmic locomotor patterns; autonomous but modulated by voluntary input.

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Muscle spindle

Proprioceptive sensor within muscle that detects changes in length and rate of stretch; intrafusal fibers; reflexes prevent overstretch.

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Golgi tendon organ (GTO)

Proprioceptor in tendons that senses muscle tension; sends information to spinal cord and cerebellum to regulate force.

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Upper motor neuron disorders

Damage to upper motor neurons (often in cortex) causing weakness, poor fine control, hypertonia, spasticity; may show Babinski sign.

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Lower motor neuron disorders

Damage to α-motor neurons causing paresis, atrophy, hypotonia; weakness without the UMN signs like Babinski.

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Basal nuclei disorders

Dyskinesia, akinesia, hypokinesis; diseases include Parkinson’s and Huntington’s.

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Cerebellum disorders

Loss of coordination, postural imbalance, tremor, dysmetria, hypotonia; due to autoimmune, inflammatory, tumor, or injury.

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Aging and motor pathways

Cortical thinning, fewer pyramidal neurons, fewer dopamine receptors in basal nuclei, changes in motor units; results in poorer posture, balance, strength; exercise helps prevention.