Motor Unit

A motor neuron and all of the muscle fibers that it innervates are referred to as a motor unit.  Muscle activity is controlled by these motor units.  Precise muscle movements (such as those of the eye) occur in muscles having a high ratio of motor neurons to muscle fibers.  More gross movements are controlled by motor units with motor neurons controlling hundreds of fibers.  SO muscle moves when a signal is sent to and received by a motor neuron.  That motor neuron is in charge of a bundle for muscle fibers.  That bundle under the neuron's supervision is called a motor unit.  The more precise the movement the smaller the bundle. It's like mobilizing an army verses a small elite unit.  Precision comes through economy and power comes from the combined effort of many.  Recognizing this can influence how one trains and designs programs.