Cranial Nerve III - Oculomotor Nerve
Figure 9. Cranial Nerve III - Oculomotor Nerve
The oculomotor nerve, unlike the previous two nerves, has more than one type of fiber. As its name indicates they are all motor fibers, in this case, somatic motor and parasympathetic motor. The nerve itself leaves the brain and travels through the superior orbital fissure into the orbit. Once there it divides to innervate four of the six muscles that control eye movement, , , , the muscle that controls the upper eyelid, the plus provides autonomic (visceral) innervation to the smooth muscles in the eye. The smooth muscles of the eye are the ciliary muscles which control the shape of the lens thus changing the focal length of the eye to adjust for the distance to the object being observed and the iris which controls the size of the pupil to adjust for different light intensities. While the outflow of this nerve is parasympathetic the nerve is joined by sympathetic nerves along its course to those two muscles.