The document discusses the somatic motor system and motor control. It covers: 1) The somatic motor system includes muscles controlled by the central nervous system like skeletal muscles. Motor neurons in the spinal cord and brain coordinate muscle contractions. 2) The motor unit consists of an alpha motor neuron and the muscle fibers it innervates. Motor neurons vary the firing rate and recruit additional motor units to finely control muscle contraction. 3) The spinal cord contains circuits that generate reflexes like the stretch reflex to control muscles. Proprioceptive feedback regulates muscle tension and coordination.