What is "trochlear nerve"

Trochlear \Troch"le*ar\, n. [L. trochlea block or pulley.] (Anat.) Shaped like, or resembling, a pulley; pertaining to, or connected with, a trochlea; as, a trochlear articular surface; the trochlear muscle of the eye.

Trochlear nerve. See Pathetic nerve, under Pathetic.

n. (context anatomy English) A motor nerve that innervates the superior oblique muscle of the eye.

n. either of the two cranial nerves on either side that control the superior oblique muscles of the eyes [syn: trochlear, trochlearis, fourth cranial nerve]

The trochlear nerve, also called the fourth cranial nerve or cranial nerve IV, is a motor nerve (a somatic efferent nerve) that innervates only a single muscle: the superior oblique muscle of the eye, which operates through the pulley-like trochlea.

The trochlear nerve is unique among the cranial nerves in several respects:

1. It is the smallest nerve in terms of the number of axons it contains.
2. It has the greatest intracranial length.
3. It is the only cranial nerve that exits from the dorsal (rear) aspect of the brainstem.
4. It innervates a muscle, Superior Oblique muscle, on the opposite side (contralateral) from its origin.

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.