<P> A motor unit is made up of a motor neuron and the skeletal muscle fibers innervated by that motor neuron's axonal terminals . 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 . The concept was proposed by Charles Scott Sherrington . </P> <P> 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 . </P>

What are the muscle fibers under the control of a single motor axon