Autonomic Nerves to the Eyes. The eye is innervated by both parasympathetic and sympathetic nerve fibers, as shown in Figure 51-11. The parasympathetic pregan-glionic fibers arise in the Edinger-Westphal nucleus (the visceral nucleus portion of the third cranial nerve) and then pass in the third nerve to the ciliary ganglion, which lies immediately behind the eye. There, the pre-ganglionic fibers synapse with postganglionic parasym-pathetic neurons, which in turn send fibers through ciliary nerves into the eyeball. These nerves excite (1) the ciliary muscle that controls focusing of the eye lens and (2) the sphincter of the iris that constricts the pupil.
The sympathetic innervation of the eye originates in the intermediolateral horn cells of the first thoracic segment of the spinal cord. From there, sympathetic fibers enter the sympathetic chain and pass upward to the superior cervical ganglion, where they synapse with postganglionic neurons. Postganglionic sympathetic fibers from these then spread along the surfaces of the carotid artery and successively smaller arteries until they reach the eye. There, the sympathetic fibers
Basic types of strabismus.
Autonomic innervation of the eye, showing also the reflex arc of the light reflex. (Modified from Ranson SW, Clark SL: Anatomy of the Nervous System: Its Development and Function, 10th ed. Philadelphia: WB Saunders, 1959.)
innervate the radial fibers of the iris (which open the pupil) as well as several extraocular muscles of the eye, which are discussed subsequently in relation to Horner's syndrome.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.