A motor unit is made up of a motor neuron and the skeletal muscle fibers innervated by that motor neuron's axonal terminals.[1] Groups of motor units often work together to coordinate the contractions of a single muscle; all of the motor units within a muscle are considered a motor pool.
All muscle fibres in a motor unit are of the same fibre type. When a motor unit is activated, all of its fibres contract. In vertebrates, the force of a muscle contraction is controlled by the number of activated motor units.