For different kinds of sensations, different kinds of receptor cells. Rod and cone cells of the eye's retina are specialized to respond to the electromagnetic radiation of light. The ear's receptor neurons are topped by hair bundles that move in response to the vibrations of sound. Olfactory neurons at the back of the nose respond to odorant chemicals that bind to them. Taste receptor cells on the tongue and the back of the mouth respond to chemical substances that bind to them. Meissner's corpuscles are specialized for rapid response to touch, while free nerve endings bring sensations of pain.

Illustration: Eade Creative Services Inc./George Eade illustrator (rod and cone cells adapted from Scientific American Vol. 256, No. 2, page 42, 1987)