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Motor Nerve Fibers

Motor Neurons

Stimulate skeletal muscle contraction from the central nervous system (CNS).

Motor Unit

One motor neuron and all the muscle fibers it stimulates.

Motor units vary...

in the number of muscle cells involved, depending on the strength or delicacy needed for the area in which they are found.

In the eye

very small, precise movements are required, One motor neuron may control only 10-15 muscle cells

In the hand

both precision and strength are needed, each motor nerve may synaps with 10-100 muscle cells

Single motor neuron

may innervate as few as 10 and as many as 2000 muscle fibers.


average muscle fibers per motor neuron

All or None Principle

Muscles contract all the way or not at all. Individual muscle fibers contract to their fullest extent. They do not partially contract.

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