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Vocabulary flashcards covering key terms and definitions from the lecture notes on Motor Pathways.
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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.
Alpha (a) motor neurons
Innervate extrafusal muscle fibers; part of a motor unit; drive actual muscle contraction.
Gamma (γ) motor neurons
Innervate intrafusal muscle fibers within muscle spindles; regulate spindle sensitivity; contract only marginally.
Motor unit
One α-motor neuron and all of the skeletal muscle fibers it innervates; size can be large or small.
Interneurons
Provide communication between neurons; relay impulses to multiple CNS areas and help synchronize complex motor pathways.
Motor cortex
Region where α-motor neurons originate; controls voluntary skeletal muscle movement; most neurons decussate before synapsing with LMNs.
Betz cells
Large pyramidal neurons in Layer V of the primary motor cortex.
Homunculus (somatotopy)
Map of the body on the motor cortex showing which cortical areas control different body parts.
Premotor cortex
Works with primary motor cortex; plans responses to visual/sound cues; stores motor memory and context.
Supplementary motor area
Assists motor cortex; coordinates complex or sequential movements; involved in bilateral movements and planning strength, distance, direction.
Association cortex
Located in the prefrontal and posterior parietal regions; modulates motor movements initiated in the motor cortex.
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.
Thalamus (motor role)
Receives basal ganglia input and provides excitatory feedback to the motor cortex to help regulate movement.
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.
Direct (pyramidal) tracts
Voluntary motor pathways; direct cortex-to-spinal cord/brainstem connections; include corticobulbar and corticospinal tracts.
Indirect (extrapyramidal) tracts
Involuntary motor pathways that modulate muscle tone and balance; originate in the brainstem and project to the spinal cord.
Corticobulbar tracts
Control skeletal muscles of chewing, facial expression, tongue movement, and swallowing; synapse with brainstem cranial nerve nuclei.
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).
Lateral corticospinal tract
Decussates at the pyramids of the medulla; mainly innervates appendicular (limb) muscles.
Ventral (anterior) corticospinal tract
Does not decussate at the medulla; innervates axial (trunk) muscles; some fibers may cross at spinal level.
Vestibulospinal tracts
Indirect tracts that control balance and posture; lateral (from lateral vestibular nuclei) and medial (from medial vestibular nuclei).
Reticulospinal tracts
Indirect tracts that control axial/postural muscles and locomotion; medial (pontine) facilitates extensors; lateral (medullary) inhibits extensors.
Rubrospinal tract
Originates in the red nucleus; mainly influences flexor muscles in humans; decussates and runs with lateral corticospinal tract.
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.
Central pattern generator (CPG)
Network of neurons generating rhythmic locomotor patterns; autonomous but modulated by voluntary input.
Muscle spindle
Proprioceptive sensor within muscle that detects changes in length and rate of stretch; intrafusal fibers; reflexes prevent overstretch.
Golgi tendon organ (GTO)
Proprioceptor in tendons that senses muscle tension; sends information to spinal cord and cerebellum to regulate force.
Upper motor neuron disorders
Damage to upper motor neurons (often in cortex) causing weakness, poor fine control, hypertonia, spasticity; may show Babinski sign.
Lower motor neuron disorders
Damage to α-motor neurons causing paresis, atrophy, hypotonia; weakness without the UMN signs like Babinski.
Basal nuclei disorders
Dyskinesia, akinesia, hypokinesis; diseases include Parkinson’s and Huntington’s.
Cerebellum disorders
Loss of coordination, postural imbalance, tremor, dysmetria, hypotonia; due to autoimmune, inflammatory, tumor, or injury.
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.