ABSTRACT
A motor unit consists of a motor neuron and the muscle fibers it innervates. In mammals each muscle fiber is supplied by only one motor neuron. However, each motor neuron synapses with anything from six to a few thousand muscle fibers within a single muscle. The size of a motor unit is related to the precision of motor control required of a given muscle. Finely regulated muscles (e.g., extraocular eye muscles) consist of small motor units, less finely regulated muscles have larger ones. The fibers of a single unit are scattered widely throughout a muscle so no part of a muscle is controlled by just one motor unit.
