Afferent neurons, also called sensory neurons, are the nerve fibers responsible for bringing sensory information from the outside world into the brain. Sensory information may involve special senses, such as vision, hearing, smell, or taste, as well as the sense of touch, pain, and temperature. Afferent neurons are typically associated with specialized sensory receptors that are classified according to the stimuli they respond to.
When a stimulus from the outside world is sensed by the sensory receptors (e.g., touching a hot pan) the sensory afferent neurons send information about that stimulus up the
spinal cord to the brain where association neurons will decide how to respond. Then, those association neurons will communicate with the motor
efferent neurons, thereby sending information down the spinal cord and out towards the muscles, indicating what motion to perform (e.g., pulling away from the hot pan).