Sensory nerves. — The sensory nerves of the human body lead from regions near the surface of the body to the central organs of the nervous system. The outer ends of these nerves are exposed in such a way as to be excited or set into commotion by physical disturbances in the region surrounding the body. This commotion is transmitted to the central organs producing commotion there, and we perceive what we call a sensation. The physical disturbance which excites a nerve is called a stimulus.