Question

What cranial nerves are responsible for movement of the eyeballs?

		oculomotor, trochlear and abducens
		oculomotor, trigeminal and abducens
		trigeminal, trochlear and abducens
		none of the above

Answer 1

Cranial nerves are nerves that originate in brain, especially in cerebellum and brainstem. There are 12 cranial nerves (CN) known. Of these four nerves are involved in functioning of the eye. These are optic nerve (CN II), oculomotor nerve (CN III), Abducens nerve (CN VI) and Trochelar nerve (CV IV). The oculomotor nerve innervates the pupil, lens, upper eyelid and eye muscles affecting the position of eyelids and pupil size. It originates in brainstem and is a motor nerve that innervates the eye and ciliary muscles, along with tear glands. It helps to keep object in focus even when the object alters it position (gaze fixation) and to track its position (visual tracking). It also is involved in pupillary light reflexes that control the amount of light entering the eye. Innervation of the levator palpebrae superioris muscle by this nerve allows elevation of upper eyelids.

The abducens nerve is a somatic motor nerve that arises from pons in brainstem and terminates in lateral rectus muscle (extraocular muscle). This muscle is involved in abduction of the eyeball on ipsilateral side. It also partially innervates the medial rectus muscle for coordinated lateral movement.

Trochlear nerve is the smallest nerve with a dorsal exit from the brainstem and innervates the superior oblique muscle. It is a somatic efferent motor nerve that causes the eyeball to rotate via abduction function and intorsion.

Optic nerve is a sensory nerve connecting retina with temporal lobe of cerebral hemisphere. It is not involved in eyeball movement. It only transfers the signals from retina to the brain.

Trigeminal nerve is the nerve involved in transmission of sensation to the face and movement of jaw muscles.

Right choice: oculomotor, trochlear and abducens.