The trochlear nerve (the fourth cranial nerve, also called the fourth nerve, IV) is a motor nerve (a “somatic efferent” nerve) that innervates a single muscle: the superior oblique muscle of the eye.
The trochlear nerve is unique among the cranial nerves in several respects. It is the smallest nerve in terms of the number of axons it contains. It has the greatest intracranial length. Other than the optic nerve (cranial nerve II), it is the only cranial nerve that decussates (crosses to the other side) before innervating its target. Finally, it is the only cranial nerve that exits from the dorsal aspect of the brainstem.
Homologous trochlear nerves are found in all jawed vertebrates. The unique features of the trochlear nerve, including its dorsal exit from the brainstem and its contralateral innervation, are seen in the primitive brains of sharks.
The human trochlear nerve is derived from the basal plate of the embryonic midbrain.
Read more about Trochlear Nerve: Peripheral Anatomy, Actions of The Superior Oblique Muscle, Central Anatomy
Famous quotes containing the word nerve:
“Tom: All right, boys. C’mon. Why don’t you say I’m a yellow belly and a big mouth at that?
Shep: You yellow? Who thinks you’re yellow? Did you hear what he said? A guy who’s got the nerve to marry? That’s more than Flash Gordon ever did.”
—Billy Wilder (b. 1906)