Chapter 6 Special Sensory Organs: Eye and Ear 239 The lens, located behind the pupil, focuses the light onto the retina. The retina (RĔT-ĭ-nă), the innermost layer of the eye, receives images formed by the lens. It contains light-sensing cells responsible for color vision and fine detail. The retina acts much like camera film—or, in today’s technology, the memory card inside a cell phone that carries information about the subscriber’s identity. The retina sends information via the optic nerve to the brain for interpreta- tion. The sclera (SKLĒ-ră) is the white, outer protective layer of the eye. The Ear The ear has three main parts: the external (outer) ear, the middle ear, and the internal (inner) ear (Figure 6.2 on the next page). Sound waves enter the external ear, or external auditory meatus (mē-ĂT-ŭs), and pass through the middle ear to the tympanic (tĭm-PĂN-ĭk) membrane (eardrum), causing it to vibrate. Vibrations in the eardrum are transmitted to the internal ear by three very small bones called ossicles. The vibrations are detected by sensory recep- tors in the inner ear, where the information is transmitted by nerve impulses to the brain. The brain interprets these neural impulses as sound. Besides the function of hearing, the ear is responsible for your sense of equilibrium, or balance. Fluid in the semicircular canals, tiny channels within the inner ear, control orientation and balance. They help you maintain steadi- ness while standing or walking. Anatomy and Physiology Vocabulary Now that you have been introduced to the basic anatomy and physiology of the eye and the ear, we will explore in more detail the key terms presented in the introduction (see table on the next page). Optic nerve Macula Sclera Retinal blood vessels Retina Cornea Iris Lens Figure 6.1 Major structures of the eye