The Oculomotor Nerves (III) PDF

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The Oculomotor Nerves (III)...

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The Oculomotor Nerves (III) ■ Primary function: Motor (eye movements) ■ Origin: Midbrain ■ Pass through: Superior orbital fissures of sphenoid pp. 213, 220, 222, 225 ■ Destination: Somatic motor: superior, inferior, and medial rectus muscles; inferior oblique; levator palpebrae superioris. Visceral motor: intrinsic eye muscles The midbrain contains the motor nuclei controlling the third and fourth cranial nerves. Each oculomotor nerve (III) innervates four of the six extrinsic muscles that move the eye, and the levator palpebrae superioris, which raises the upper eyelid (see Figure 14–21). On each side of the brain, CN III emerges from the ventral surface of the midbrain and penetrates the posterior wall of the orbit at the superior orbital fissure. Individuals with damage to this nerve often complain of pain over the eye, droopy eyelids, and double vision, because the movements of the left and right eyes cannot be coordinated properly. The oculomotor nerve also delivers preganglionic autonomic fibers to neurons of the ciliary ganglion. These neurons control intrinsic eye muscles. These muscles change the diameter of the pupil, adjusting the amount of light entering the eye. They also change the shape of the lens to focus images on the retina. The Trochlear Nerves (IV) ■ Primary function: Motor (eye movements) ■ Origin: Midbrain ■ Pass through: Superior orbital fissures of sphenoid pp. 213, 219, 222, 225 ■ Destination: Superior oblique A trochlear (TRO . K-le . -ar; trochlea, a pulley) nerve (IV), the smallest cranial nerve, innervates the superior oblique of each eye (Figure 14–21). The trochlea is a pulley-shaped, ligamentous sling. Each superior oblique passes through a trochlea on its way to its insertion on the surface of the eye. An individual with damage to cranial nerve IV or to its nucleus has difficulty looking down and to the side. The Abducens Nerves (VI) ■ Primary function: Motor (eye movements) ■ Origin: Pons ■ Pass through: Superior orbital fissures of sphenoid pp. 213, 219, 222, 225 ■ Destination: Lateral rectus The abducens (ab-DU . -senz) nerves (VI) innervate the lateral rectus, the sixth pair of extrinsic eye muscles. Contraction of the lateral rectus makes the eye look to the side. In essence, the abducens causes abduction of the eye. Each abducens nerve emerges from the inferior surface of the brainstem at the border between the pons and the medulla oblongata (Figure 14–22). Along with the oculomotor and trochlear nerves from that side, it reaches the orbit through the superior orbital fissure....