what does the peripheral nervous system do
1 The central nervous system is made up of the brain and spinal cord. 2  The peripheral nervous system is made up of the nerve fibers that branch off from the spinal cord and extend to all parts of the body, including the neck and arms, torso, legs, skeletal muscles and internal organs.he brain sends messages through the spinal cord and nerves of the peripheral nervous system to control the movement of the muscles and the function of internal organs. The basic working unit of the nervous system is a cell called a neuron. The human brain contains about 100 billion neurons.