Anatomy & Physiology I and II

Anatomy & Physiology Study Guide • The taste buds are monitored by cranial nerves that synapse within the solitary nucleus of the medulla oblongata. Postsynaptic neurons carry the nerve impulses on to the thalamus, where third- order neurons project to the primary sensory cortex. Internal eye structures contribute to vision, while accessory eye structures provide protection: • The accessory composition of the eye includes the eyelids (palpebrae), separated by the palpebral fissure, the eyelashes, and the tarsal glands. • An epithelium, called the conjunctiva, covers most of the exposed surface of the eye. The cornea is transparent. • The secretions of the lacrimal gland contain lysozyme. Tears collect in the lacrimal lake and reach the inferior meatus of the nose after they pass through the lacrimal puncta, the lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct. • The eye has three layers: an outer fibrous tunic, a middle vascular tunic, and an inner neural tunic. • The fibrous tunic consists of the sclera, the cornea, and the corneal limbus. • The vascular tunic, or uvea, is composed of the iris, the ciliary body, and the choroid. The iris contains muscle fibers that alter the diameter of the pupil. The ciliary body is made of the ciliary muscle and the ciliary processes, which adhere to the suspensory ligaments of the lens. • The neural tunic, or retina, consists of an outer pigmented part and an inner neural part; the latter contains visual receptors and associated neurons. • The retina contains two types of photoreceptors: rods and cones. • Cones are densely grouped in the fovea, at the center of the macula lutea. • The direct line to the CNS goes from the photoreceptors to bipolar cells, then to ganglion cells, and, finally, to the brain via the optic nerve. The axons of ganglion cells converge at the optic disc, known as the blind spot. Horizontal cells and amacrine cells modify the signals passed among other components of the retina. • 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: ©2018 Achieve Test Prep Page 202 of 367