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Flashcards in Motor Units Deck (8)
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Motor Pool

MNs coming out from spinal cord that activate a specific uscle


5 Kinds of Neurons that Synapse Onto Lower Motor Neurons

Short and long distance local circuit neurons
Commissural Axons - (LD local circuits that decussate)
Input from UMNs (descending input from cortex)
Sensory input from muscle Rs


Motor Unit

1 LMN and all of the muscle fibers it innervates. All are of same type and in a mosaic in the muscle


Muscle Examples of Mostly Fast and Mostly Slow Fibers

Gastroc: fast
Soleus: slow


3 Mechs of Graded Contraction

Increase firing rate
Recruit additional motor units and synergistic muscles


2 Stronger Forces of Fast Motor Units

Fast Fibers produce more force each and there's more of them in a motor unit


Motor Unit Recruitment

Small diameter MNs are for slow and have few channels, and thus high resistance and so a stimulus causes a high V. Large diameters are for fast, so it requires more. So slow units recruited first, once they reach a certain point they recruit fast units. Fasts fatiguables activated last


Acute Denervation and Reinnervation

Acute Denervation if a motor neuron dies/axon is injured, myofibers of its unit atrophy rapidly and so mosaic of normal and atrophied fibers. If healthy axons adjacent and it stays dead, healthy ones sprout w/in few weeks and reinnervate muscle fibers but will cause fiber type conversion so big blocks less well regulated, less graded, and have large fasciculations