The role of nerves is mainly to innervate the sensory and motor functions of various tissues and organs of the body. The nervous system is divided into two parts: the central nervous system, including the brain and spinal cord, and the peripheral nervous system, including the cerebral nerves, spinal nerves and vegetative nerves: 1. The brain sends motor information to all parts of the limbs, or all parts of the body send sensory information to the brain, etc. The spinal cord is needed for conduction. In addition, the spinal cord, as a low-level center, can govern simple reflex activities, i.e., reflex arcs that do not pass through the brain, such as the stretch reflex, muscle inhibition reflex, superficial reflex, bladder urination reflex, rectal defecation reflex, etc. Peripheral nervous system 1. Cerebral nerves: 12 pairs of cerebral nerves are emitted, mainly innervating the motor and sensory functions of various tissues and organs of the head and face; 2. Spinal nerves: 31 pairs of spinal nerves are emitted from the spinal cord, including 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 pair of pudendal nerves. The spinal nerves are mixed nerves, mainly innervating the motor and sensory functions of the trunk and viscera; 3, the vegetative nerves: divided into sympathetic and parasympathetic nerves, sympathetic nerves emanate from the spinal nerves, which are responsible for exciting various activities of the viscera, cardiovascular and glandular bodies. Parasympathetic nerves are divided into cerebral and spinal sacral, often travel in the cerebral or spinal nerves, mainly inhibiting the activities of the viscera, cardiovascular and glandular.