Anatomy & Physiology

Anatomy & Physiology Study Guide • The ciliary lens and body divide the interior of the eye into a large posterior cavity, or vitreous chamber, and a smaller anterior cavity. The anterior cavity is subdivided into the anterior chamber, which extends from the cornea to the iris, and a posterior chamber, between the iris and the ciliary body and lens. • The fluid aqueous humor moves within the eye and reenters circulation after diffusing through the walls of the anterior chamber and into the canal of Schlemm. • Light is refracted (bent) when it travels through the cornea and lens. Throughout accommodation, the shape of the lens changes to focus an image on the retina. “Normal” visual acuity is rated 20/20. • The lens focuses an image on the photoreceptors. The condition in which a lens has lost its transparency is a cataract. • The lens lies posterior to the cornea and forms the anterior boundary of the posterior cavity. This cavity contains the vitreous body, a gelatinous mass that helps stabilize the shape of the eye and supports the retina. Photoreceptors respond to light and change it into electrical signals essential to visual physiology: • The two kinds of photoreceptors are rods, which respond to almost any photon regardless of its energy content, and cones, which have characteristic ranges of sensitivity. • Each photoreceptor contains an outer segment with membranous discs. A narrow stalk connects the outer segment to the inner segment. Light absorption occurs in the visual pigments, which are derivatives of rhodopsin (opsin plus the pigment retinal, which is synthesized from vitamin A). • Color sensitivity is dependent upon the integration of information from red, green, and blue cones. Color blindness is the inability to detect certain colors. • In the dark-adapted state, most visual pigments are fully receptive to stimulation. In the light- adapted state, the pupil constricts, and bleaching of the visual pigments occurs. • The ganglion cells that monitor rods, called M cells (magnocells), are relatively large. The ganglion cells that monitor cones, called P cells (parvo cells), are smaller and more numerous. • Visual data from the left half of the combined field of vision arrive at the visual cortex of the right occipital lobe; data from the right half of the combined field of vision arrive at the visual cortex of the left occipital lobe. • Depth perception is obtained by comparing relative positions of objects between the left and right eye images. • Visual contributions of the hypothalamus’ suprachiasmatic nucleus affect the function of other brainstem nuclei. This nucleus establishes a visceral circadian rhythm, which is tied to the day–night cycle and affects other metabolic processes. Equilibrium sensations originate within the inner ear, while hearing involves the detection and interpretation of sound waves: • Equilibrium and hearing are supplied by the inner ear’s receptors. • The ear is categorized into the external ear, the middle ear, and the inner ear.

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