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 15 of 16 Lower Motor Neuron (LMN) Lesions Due to the close proximity of the oculomotor and Edinger-Westphal nuclei and the fact that the fibers of both components travel together all the way to the orbit of the eye, a LMN lesion will most likely affect both components of CN III. The following collection of signs and symptoms, known as oculomotor ophthalmoplegia, is characteristic of a CN III LMN damage. Downward, abducted eye on the affected side due to the unopposed actions of the superior oblique and lateral rectus muscles. Strabismus (the inability to direct both eyes toward the same object) as a result of extraocular muscle paralysis. This leads to diplopia (double vision). Ptosis (eyelid droop) on the affected side due to inactivation of levator palpebrae superioris muscle and the unopposed action of the orbicularis oculi muscle (innervated by CN VII). The patient may compensate for the ptosis by contracting the muscles of the forehead to raise the eyebrow and lid. Dilation of the pupil on the affected side due to decreased tone of the constrictor pupillae muscle. Loss of the accomodation reflex on the affected side. Figure 3-15. Lower Motor Neuron (LMN) Lesions. Because upper motor neuron (UMN) lesions often involve more than one of the cranial nerves, they are discussed in the Eye Movements module.

Last revised: March 22, 1998