There are 31 pairs of spinal nerves, which are divided into cervical, thoracic, lumbar, sacral, and caudal nerves. The spinal nerves are mixed nerves, which are divided into anterior and posterior roots, with the anterior roots consisting mainly of motor nerve fibers, and the posterior roots consisting mainly of sensory nerve fibers. Spinal nerves, also known as spinal nerves, are pairs of nerves emanating from the spinal cord, with a total of 31 pairs, 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 caudal nerves, for a total of 31 pairs. The spinal nerves are mixed nerves and contain four fiber components: somatic motor fibers, somatic sensory fibers, visceral motor fibers, and visceral sensory fibers. Spinal nerves are distributed on both sides of the spinal cord, and each side is divided into anterior and posterior roots. The anterior root consists of the axons of motor neurons in the anterior horn of the spinal cord and the axons of sympathetic or parasympathetic neurons in the lateral horn; the posterior root consists of the axons of sensory neurons, whose endings are distributed in all parts of the body, and which are capable of sensing various stimuli.