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31 Cards in this Set
- Front
- Back
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Where are LMN located?
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Ventral horn
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Somatotropic organization of LMN?
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-Motor neurons for axial muscles are medial,
-Lateral for more distal muscles -Flexor motor neurons are dorsal to extensor motor neurons |
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Alpha motor neurons
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extrafusal fibers
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gamma motor neurons
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intrafusal fibers
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Each muscle fiber receives contact from ________ motor neurons?
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1
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When a motor neuron generates an action potential,_________________ in the motor unit contract
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all of the muscle fibers
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Red fibers
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-aka Slow oxidative fibers
– slow, sustained movements - example posture |
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Intermediate fibers
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- aka Fast oxidative fibers
– intermediate in speed and fatigue - example Walking |
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White fibers
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-aka Fast glycolytic fibers
– fast, brief movements -examples Jumping & Sprinting |
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Slow twitch motor unit
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-aka type S motor unit
-small amts of force for an extended time -red fibers |
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Fast twitch, fatigable motor unit
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-aka type FF
-large amt of force for brief periods of time -white fiber |
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Fast twitch, fatigue resistant motor unit
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-moderate amt of force over a moderate time
-intermediate fibers |
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Recruitment of motor units
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– increasing the number of active motor units
-recruited in order of size S-->FR-->FF |
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tetanus
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a smoothly fused contraction that results from rapid stim to muscle tissue
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Motor Unit Summation
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-temporal
-repeated stim causes repeated muscle twitches that add to each other to cause a greater than twitch response to a single stim -muscle does not have time to completely relax btwn stim |
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descending pathways, what's there typical MO?
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-LMN are regulated by supraspinal centers
-UMN synapse with and direct either LMN or interneurons |
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Where are UMN located?
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cerebral cortex or brainstem
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what do cortical spinal tracts due?
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mediate voluntary movement
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Where do corticospinal tracts originate?
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-1/2 from contralateral primary motor cortex
-1/3 from contralateral frontal cortex (premotor and supplementary motor areas) -From contralateral parietal cortex association areas |
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What is the role of the cortex in mvt generation?
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association cortex decides on mvt, premotor cortex devises a plan, basal ganglia/cerebellum provide fine tuning and motor cortex executes. Info is then projected into the spinal cord (LMN) who effect the change
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Lateral Corticospinal Tract
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-major descending pathway of the spinal cord, 85% of the fibers are from the contralateral pyramid
-ends in ventral horn in on interneurons or motor neurons |
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pathway of the lateral corticospinal tract
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motor cortex-->internal capsule-->peduncle, pons, medullary pyramid (CROSS)-->lateral corticospinal tract to specific level ventral horn
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What does damage to the lareral corticospinal tract result in?
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-inability to use fingers individually, eg pincer grip
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Upper Motor Neurons
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-Precentral gyrus
-Contact other neurons -Spastic paraylsis (increased tone/reflex) |
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Lower motor neurons
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-Ventral/anterior horn
-Contact skeletal muscle -Flaccid paralysis (decreased tone/reflex) |
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Anterior Corticospinal Tract
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-15% of fibers in each pyramid that do not cross (from ipsilateral pyramid) continue into anterior funiculus as anterior corticospinal tract
-many cross over in the ant. white comissure -terminate in med. ventral horn either with LMN or interneurons |
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Anterior Corticospinal Tract muscle activation
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-Preferentially affect the activity of motor neurons for axial muscles
-mostly in cervical and thoracic |
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What deficiets does damage to the ant. corticospinal tract result in?
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Does not result in obvious weakness, this is probably because of bilateral distribution of fibers from the contralateral tract
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Vestibulospinal tract
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- a descending tract that affects postural adjustment and head movements
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Reticulospinal / rubrospinal tracts
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a descending pathway that affects alternate routes of movement mediation
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Tectospinal tract
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a descending pathway that helps coordinates head movements with visual stim.
-believed to be involved in turning of head in response to visual stim |
