IV.B.1 Head: Nasal & Orbital Region

IV.B.1 Head: Nasal & Orbital Region Page 5 of 6

Trochclear CN IV

Step 6: View the trochlear nerve.

	Where does the trochlear nerve exit the brain stem?
It is the only cranial nerve to exit from the posterior brain stem. It is also the longest cranial nerve.
	What foramen does it pass through to exit the skull?
Superior orbital fissure.
	What muscles does it control?
Superior oblique.

The superior oblique has a pulley mechanism. In Latin, a trochlea is a pulley. This is the derivation of the naming of the trochlear nerve.

	The traochlear nerve crosses from left to right and right to left as it exits the the posterior brain stem. Why does this make sense?
The Superior orblique muscle controls medial and downward gaze from the medial (nasal) side of the eyeball. Since the nasal retinal fibers of the optic nerve must cross to help contralateral vision, the contralateral side of the brain controls the superior oblique muscle for lateral vision.