Chapter 8: Special Senses

People are responsive creatures. Hold freshly baked bread before us, and our mouths water. A sudden clap of thunder makes us jump. These "irritants" (the bread and the thunderclap) and many others are the stimuli that continually greet us and intercepted by our nervous system.

We are usually told that we have five senses that keep us in touch with what is going on in the external world: touch, taste, smell, sight, and hearing. Actually touch is a mixture of the general senses that we considered in Chapter 7-the temperature, pressure, and pain receptors of the skin and the proprioceptors of muscles and joints. The other four "traditional" senses-smell, taste, sight, and hearing-are called special senses. Receptors for a fifth special sense, equilibrium, are housed in the ear, along with the organ of hearing. In contrast to the small and widely distributed general receptors, the special sense receptors are either large, complex sensory organs (eyes and ears) or localized clusters of receptors (taste buds and olfactory epithelium).

This chapter focuses on the functional anatomy of each of the special sense organs individually, but keep in mind that sensory inputs are overlapping. What we finally experience-our "feel" of the world-is a blending of stimulus effects.