Neurons are nerve cells, which are the most basic components of the nervous system, including the central nervous system and the peripheral nervous system, and most neurons are located in the central nervous system. The main role of sensory neurons is to receive external stimuli and to transmit nerve impulses to the central nervous system, so they are also called sensory afferent neurons, and after the nerve impulses are transmitted, they are analyzed and fed back. Motor neurons, also known as motor efferent neurons, are responsible for transmitting nerve impulses from the nerve cell, through the axon to the terminal, and connecting with muscles and other glands to produce motor contractions in muscles and secretion of endocrine hormones in glands. Contact neurons, also known as interneurons, receive impulses from other neurons and transmit them to another neuron.