Fundamentals of Sensory Systems

In bringing information about the world to an individual, sensory systems perform a series of common functions. At its most basic, each system responds with some specificity to a stimulus, and each employs specialized cells-the peripheral receptors-to translate the stimulus into a signal that all neurons can use. Because of their physical or chemical specialization, the many types of receptors transduce the energy in light, heat, mechanical, and chemical stimulation into a change in membrane potential. That initial electrical event begins the process by which the central nervous system (CNS) constructs an orderly representation of the body and of things visible, audible, or chemical. To bridge the distance between peripheral transduction and central representation, messages are carried along lines dedicated to telling the CNS what has taken place in the external world and where it has happened. Such precision requires that labor be divided among neurons so that not only different stimulus energies (light vs. mechanical deformation) but also different stimulus qualities (steady indentation vs. high-frequency vibration of the skin) are analyzed by separate groups of neurons.