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22 Cards in this Set
- Front
- Back
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define motor unit
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one motor neuron and all of the muscle FIBERS it inervates
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What is the relationship between size of the motor unit and precision of control
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smaller unit= more control (stapedius 1MN=2-3 fibers, gastrocnemius 1MN=1000 fibers)
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How do alpha and gamma MN's differ in terms of innervation
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alpha=extrafusal fibers, gamma=intrafusal fibers
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Describe the structure of a motor unit in normal muscle
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1 MN innervates many muscle fibers in DIFFERENT fascicles, the innervated fibers are not adjacent to each other, allows for efficicent activation of muscle in proportion to the force necessary, asynchronous activation= smooth fluid movement
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T/F a motor unit innervates many muscles fibers that are all in one fascicle
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false, this indicates pathology (deinnervation=>reinnervation), larger muslce unit=larger increments of force=large, jerky movements, not finely graded, loss of asynchrony
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What are some histological clues that a muscle is diseased
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Normally both types of muscle fiber are evenly distributed in a random fashion, w/ pathology can have fiber type grouping
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how can you distinguish a neuropathic vs. myopathic disorder based on MUP duration and amplitude
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neuropathic=MUPs are large and long b/c reinnvation of a larger region=abnormally large motor unit, mypathic=reduced amplitude and duration because of damage to muslce itself
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How can you distinguish between a neuropathic and myopathic disorder based on recruitment pattern
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neuropathic=normal amplitude but interrupted firing since some motor units are not sucessfully activated (the intact units work just fine but you skip the messed up ones);
myopathic=continous or increased pattern sincemore motor units need to be activated for a given force but the amplitude is decreased (the pattern is the same because all of the nerves are working but the amplitude is decreased becasue there are less working muscle cells Hint: Amplitude is determined by muscle cells, pattern is determined by nerve cells |
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Describe the shape of an EMG for a damaged muscle that has undergone de/re innervation
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at rest=fasiculations, random firing; slight contraction=large force b/c MN innervates a larger unit; maximal contraction=reduced interference pattern b/c fewer healthy nerves to generate force
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describe the somatotopic organization of the motor nuclei in the ventral horn of the spinal cord
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medial=axial muscles, lateral=limb muscles (most medial=proximal, more lateral- distal), flexors are nera the center of the spinal cord, extensors are more peripheral
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how does the "connectivity" of medial and lateral nuclei differ
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medial=connected across many segments (balance, posture), lateral= few segments
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compare UMN and LMN lesions in terms of: weakness
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weakness is expected for both
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compare UMN and LMN lesions in terms of: atrophy
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UMN= no atrophy, LMN= atrophy
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compare UMN and LMN lesions in terms of: fasciculations
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UMN=NO, LMN=YES
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compare UMN and LMN lesions in terms of: reflexes
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UMN=increased, LMN=decreased
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compare UMN and LMN lesions in terms of: tone
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UMN=increased LMN=decrased
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What is the function of slow twitch motor units (type 1)
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small fibers, small MN, slow contraction, small tension long duration w/o fatigue, specialized for endurance esp. posture, standing, walking
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What is the function of fast fatigalbe motor units (IIb)
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larger fibers, larger MN, prief burst of force, escape, sprint, jump
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what is the funciton of fast fatigue-resistance fibers
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endurance exercise
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what two factors determine the force exerted by a muscle
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1.rate code- frequency of AP firing in motor neuron 2. Recruitment-number of motor units firing
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Describe the order of recruitment of motor units
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correlated wit hsize of cell body and axon; slow twich first then fast twitch, fast-fatigable last, stop firing in reverse order
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What are the advantages of the "size principle" in terms of MU recruitment
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allows a smooth increase in force output by muslce, minimizes fatigue, maximuzes efficiency
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