But on exposure to light, it straightens out. This alters the three-dimensional structure of the entire rhodopsin molecule, activating it and triggering a biochemical cascade. The activated rhodopsin then stimulates transducin, a protein that belongs to the large family of so-called G proteins. Cyclic GMP carries signals from the disks, where light is absorbed, to the cell's surface membrane, which contains a large number of channels. As ions move into the cell, they alter its electrical potential.
Receptors convert energy into electrical activity.
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 back of the mouth respond to chemical substances that bind to them.