Neuron is a nerve cell, which is the most basic unit of the nervous system, including the central nervous system and the peripheral nervous system. Most neurons are distributed in the central nervous system, and according to their different roles, they are classified into three types: sensory neurons, motor neurons, and contact neurons. Sensory neurons are responsible for receiving stimuli from the outside and transmitting nerve impulses to the central nervous system, so they are also known as sensory afferent neurons, which analyze and provide feedback after the nerve impulses are transmitted. Motor neurons, also known as motor efferent neurons, are responsible for transmitting nerve impulses from the nerve cell, through the axon, to the periphery, and connect with the muscles and other glands to produce motor contractions in the muscles and secretion of endocrine hormones by the glands. Contact neurons, also known as interneurons, are able to receive impulses from other neurons and transmit them to another neuron.