The nervous system in the human body is divided into two major parts: the central nervous system and the peripheral nervous system, with the central nervous system including the brain and spinal cord. The peripheral nervous system includes the cerebral and spinal nerves, and the peripheral nerves in the human body mainly include 12 pairs of cranial nerves and 31 pairs of spinal nerves. The cranial nerves mainly include the olfactory nerve, optic nerve, ophthalmic nerve, trochlear nerve, trigeminal nerve, sphenoid nerve, facial nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve, paracentral nerve and hypoglossal nerve. Each pair of nerves has a different role and is divided into sensory, motor and mixed nerves according to its function. The spinal nerves mainly include 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and 1 pair of caudal for nerves. Each spinal nerve penetrates from the anterior root of each spinal cord stage, and from the posterior root it then passes into the spinal cord. The spinal nerves then send down many plexuses, nerve trunks, and peripheral nerves, which then pass to the neuromuscular junction to innervate the muscles. All these nerves are distributed to the bones, muscles, tissues and organs of the whole body, which is a very large and complex nerve network that includes sympathetic, parasympathetic and vegetative nerves.