Motor Unit
The functional unit of the neuromuscular system consisting of a motor neuron and all muscle fibers it innervates. Used in electrodiagnostic testing to assess neuromuscular function.
Full Definition
A motor unit comprises a single motor neuron (including its cell body, axon, and axon terminals) and all the skeletal muscle fibers that it innervates. Motor units vary in size from small units with few muscle fibers (for fine motor control) to large units with hundreds or thousands of fibers (for gross motor movements). During voluntary contraction, motor units are recruited in an orderly fashion from smallest to largest. Assessment of motor unit recruitment patterns is crucial in electrodiagnostic evaluation of neuromuscular disorders.
Usage
Usage note: Distinguish from 'motor neuron' which is only the neural component, not including muscle fibers.
In Context
- "The motor unit recruitment pattern suggested a neurogenic process." — EMG report
- "Large motor units were observed during maximal voluntary contraction." — Electrodiagnostic study