Anatomy & Physiology I and II

Anatomy & Physiology Study Guide neural tunic. The eyeball is hollow; its interior can be divided into two cavities. The large posterior cavity is also called the vitreous chamber. The smaller anterior cavity is subdivided into the anterior and posterior chambers. The form of the eye is stabilized in part by the vitreous body and the clear aqueous humor, which fills the anterior cavity. The Fibrous Tunic The fibrous tunic consists of the sclera and the cornea. The fibrous tunic provides mechanical support and some degree of physical protection, serves as an attachment site for the extrinsic eye muscles, and contains structures that assist in the process of focusing. Most of the ocular surface is protected by the sclera , or “white of the eye,” which consists of a dense fibrous connective tissue containing both collagen and elastic fibers. The six extrinsic eye muscles insert on the sclera. Small blood vessels and nerves from the surface penetrate the sclera to reach internal structures. The vessels are visible as red lines against the white background of collagen fibers. The cornea does not contain blood vessels; the tears that flow across the free surfaces of superficial epithelial cells provide oxygen and nutrients. The cornea also has numerous free nerve endings, and it is the most sensitive portion of the eye. The Vascular Tunic (Uvea) The vascular tunic, or uvea, contains numerous blood vessels, lymphatic vessels, and the intrinsic (smooth) muscles of the eye. This middle layer has many functions. These include providing a route for blood vessels and lymphatics that supply tissues of the eye, controlling the shape of the lens, regulating the light that enters the eye, and secreting and reabsorbing the aqueous humor as it circulates within the chamber. The vascular tunic includes the iris, the ciliary body, and the choroid. The iris contains blood vessels, pigment cells, and two layers of smooth muscle fibers called pupillary muscles. When these muscles contract, they change either the diameter of the pupil or central opening of the iris. Both muscle groups responsible for the contraction of the pupil are controlled by the autonomic nervous system. The ciliary body is a thickened region that begins deep to the junction between the cornea and the sclera. The iris attaches to it anteriorly. The bulk of the ciliary body consists of the ciliary muscle, which is a smooth muscular ring that projects into the interior of the eye. The connective tissue fibers of these ligaments keep the lens posterior to the iris and centered on the pupil. Subsequently, light passing through the pupil also passes through the lens. The choroid is a vascular layer that separates the fibrous and neural tunics posterior to the ora serrata. Protected by the sclera and attached to the outermost layer of the retina, the choroid contains an extensive capillary network that delivers oxygen and nutrients to the retina. The choroid also contains melanocytes, which are especially numerous near the sclera. The Neural Tunic (Retina) The neural tunic, or retina, is the innermost layer of the eye. It is made of a thin, outer layer called the pigmented part, and a thick inner layer called the neural part. Light that passes through the neural part is absorbed by the pigmented part of the retina. In addition to light receptors, the neural part of ©2018 Achieve Test Prep Page 191 of 367