238 Medical Terminology: Mastering the Basics Overview of Anatomy and Physiology of the Eye and Ear The special sensory organs contain receptors that receive information about stimuli outside the body (the external environment) and transmit neural impulses about these stimuli to the brain for interpretation. The special sen- sory organs also process and interpret information about external stimuli to help maintain internal homeostasis, a condition of stable physiological equilib- rium (balance) that allows the body to function normally. (You will learn more about homeostasis in your study of Chapter 7: The Nervous System.) Organs of the sensory system play a vital role in homeostasis by alerting the body to potential danger. For example, two college students are walking down a dark, windy street late at night after seeing a movie with some friends. They hear the muffled crunching of stones from behind them, as if someone is following them. The students quickly dart into a nearby convenience store and text their roommates, asking whether one of them can give them a ride back to their dormitory. In this scenario, both the ears and the eyes—two of the special sensory organs—play a crucial role in alerting the body to potential danger. Sensory systems of the body include the five commonly recognized sen- sory organs: Organ Function(s) Eye Sight (visual) Ear Hearing (auditory) equilibrium, or balance (vestibular) Nose Smell (olfactory) Tongue Taste (gustatory) Skin Touch (tactile or somatic) For the purposes of this chapter, we will limit our discussion of special sensory organs to the eye and the ear. The Eye The eye operates much like a camera. Incoming light passes through the cornea, similar in function to the aperture (adjustable opening) of a camera (Figure 6.1). The cornea is the clear, outer layer of the eye that covers the iris and pupil it allows light to travel to the interior of the eye. The amount of light that enters the eye is controlled by the iris, the colored portion of the anterior eye. Within the iris is an opening called the pupil, which contracts (narrows) and dilates (expands) to regulate the amount of light entering the eye, much like a camera shutter.