![]() Consequently, a mass that presses on the outside of CN III will usually impact the pupillary function first (for example as a result of an aneurysm or raised ICP). By contrast, the CN III control of eye movement and eyelid opening runs deep in the centre of the nerve. Loss of pupillary reactivity is the most important urgent CN III finding. The pupillary control provided by CN III is located along the periphery of the nerve. A new and sudden finding of pupillary dilation and loss of reactivity suggests supratentorial herniation or expanding volume at the top of the brainstem. What is the significance of monitoring for CN III function?Īcute loss of CN III function is an important sign of a raised intracranial pressure with expanding mass lesion. You can remember this function because the Oculomotor nerve starts with the letter "O" for eye "O"pening. Eyelid Elevation Cranial Nerve III also controls the ability to open the eyelid. It activated the medial rectus, superior rectus, inferior rectus and inferior oblique muscles to cause orbital rotation. The ability to move the eye in all other directions is controlled by the 3rd cranial nerve. Cranial Nerve IV (Trochlear) controls downward eye movement toward the nose, and Cranial Nerve VI (Abducens) controls horizontal eye movement toward the temple. Eye Movement The 3rd cranial nerve also controls eye muscle movement. The parasympathetic response of the pupil (or "return to normal") is constriction. Pupil Constriction Each one of the two 3rd cranial nerves controls the parasympathetic response of the pupil on the same side (ipsilateral). ![]() They control eye muscles on the same side of the body (ipsilateral). They are Lower Motor Neurons (LMN) (second order neurons). The 3rd cranial nerves are pure motor nerves. The two 3rd cranial nerves (oculomotor nerves) are located at the top of the brainstem - one to the right and one to the left.
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