Organs of Special Sense

Abstract

The eye is a fluid-filled sphere with a transparent opening through which light enters and is focused on an epithelium whose highly modified cilia are sensitive to the impact of photons. The membrane depolarization initiated by such impact is then passed through a chain of neurons to the eNS, where it is interpreted as light. In the visual cortex the patterns of this nerve activity are translated into images that represent the structure of the external world. Each globe is set in a bony protective socket (the orbit) (Fig. 19.1) within the skull and fitted with six muscles that provide the precise movement needed for the depth perception made possible by binocular vision, as well as for the coordinated tracking movements.