Chapter contents Overview Somatic motor component Origin, central course Intracranial course Final innervation Visceral motor component Origin and course Final innervation

Cranial Nerve III - Oculomotor Nerve Page 13 of 16 Visceral Motor Component, Accomodation Reflex Accommodation is an adaptation of the visual apparatus to facilitate near vision. This reflex involves the following: An increase in the curvature (and therefore the refractive power) of the lens Pupillary constriction to help sharpen the image on the retina Convergence of the eyes to fixate on the target object The accommodation pathway is summarized below: Fibers from the primary visual cortex project, via the visual association cortex of the occipital lobe, to the superior colliculi and pretectal nuclei. Axons from the superior colliculi and pretectal nuclei project to both the Edinger-Westphal and oculomotor nuclei. Signals from the Edinger-Westphal nuclei travel via the ipsilateral oculomotor nerve to reach the ciliary and constrictor pupillae muscles of the eye. Contraction of the ciliary muscle causes the lens to increase its curvature (and thus its refractive power), while contraction of the constrictor pupillae reduces the size of the pupillary aperture. Signals from the oculomotor nuclei travel via the ipsilateral oculomotor nerve to the medial rectus muscles causing them to contract and resulting in convergence of the eyes on the object of interest.

Last revised: March 22, 1998