This chapter focuses on the topic of the structure and function of the spinal cord. It also considers peripheral, cranial, spinal and cervical nerves. The spinal cord varies somewhat in thickness, swelling out in both the cervical and lumbar regions, when it gives off the large nerve supply to the limbs. These are called the cervical and lumbar enlargements. A motor impulse from the motor centre in the brain is carried by an efferent fibre down to the motor cell in the spinal cord. The spinal nerves supply the muscles of the trunk and limbs with the power of movement, and give sensation to the skin and to a lesser extent the muscles, bones and joints around the spine. There are thrity-one pairs of spinal nerves, which are mixed nerves: this means that they contain both motor and sensory fibres. They arise from the spinal cord by two roots: anterior or motor roots and posterior or sensory roots.