Term
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Definition
-motor neuron and all its muscle fibers it innervates
-motor axons branch onto many motor fibers
-vary in size (FF & S) |
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Term
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Definition
Motor units are recruited by size
-# of motor units active changes amount of force produced by muscle
-As active motor neurons increases, lower threshold S motor units recruited first
1) S= standing motor units
2) FF= jumping/leaping motor units |
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Term
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Definition
1) Fast Fibers (FF): Large motor neurons innervate large muscle fibers
-generate a lot of force
-large glycogen reserve-have energy readily available
-few mitochondria, easily fatigued
-Use when jumping, leaping, etc.
2) Slow Fibers (S), smaller motor units
-lower threshold of activation
-Generate small forces
-myoglobin, stores oxygen.
-Small motor units |
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Term
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Definition
1) Muscle Spindles
Structure: sensory receptor in muscles
Function: Respond to rate of change and change of length of muscle
-Creates sense of space for body
-stretch muscle spindles--> increased activity in alpha motor neurons that innervate muscle
-Deviations from desired muscle length detected by muscle spindles... restores muscle to desired length by constracting or relaxing muscle
-Disturbance-->length change in muscle fiber--> spindle receptors recognize and increase spindle afferent discharge-->activate alpha motor neurons
2) GTO= golgi tendon organs
Structure: junction of muscle & tendon, innervated by a single group of sensory axons
Function: Monitors and maintains muscle force
-Sensitive to muscle tension (muscle contraction)... insensitive to passive stretch (unlike spindles)
-Maintains steady level of force
-Negative feedback system that regulates muscle tension |
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Term
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Definition
-Alpha: innervates extrafusal muscle fibers
-Gamma: innervates intrafusal muscle fibers
Coactivation: prevents spindle from being unloaded. When both activated, no decrease in firing during muscle shortening |
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Term
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Definition
-Rapid response w/out direct control
-Modified by descending control... Upper motor structures do not participate in reflex itself
-Adjusted by descending system in order to control movement based on context of situation |
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Term
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Definition
-In motor cortex, encode accurate movement
-Movement in certain direction can result from summed activity of many small elements
-Vectors: direction and magnitude=firing rate
-Each neuron gets a vote for what direction... weight of vote depends on rate of discharge for the movement direction |
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