The terminal branches of the axon of a single motor

The terminal branches of the axon of a single motor neuron
can synapse with up to 1000s of muscle fibers, forming a
motor unit . A motor pool consists of multiple motor units .
The vertebrate motor unit

The vertebrate motor unit
•
muscles performing powerful, coarsely controlled
movements have larger number of fibers per motor unit

example : a single calf muscle motor neuron may
connect to ~2000 muscle fibers
•
muscles that produce more precise, delicate movements
contain fewer fibers per motor unit

example : extraocular muscles have only ~12 muscle
fibers per motor neuron
A single motor unit consists of a single motor neuron and all
the muscle fibers that it controls .
The numbers of muscle fibers per motor unit and numbers
of
motor units per muscle vary widely.

Motor units in extraocular muscles

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Treppe and summation
.
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Summation Treppe
Treppe and summation

Incomplete tetanus Complete tetanus
Tetanus