The trochlear and abducens nerves
The trochlear nerve is the fourth of the twelve cranial nerves, whereas the abducens nerve is the sixth. They both consist of afferent and efferent motoric fibers.
The word afferent means 'toward the centre', as in 'from a peripheral area of a limb to the central nervous system'. The word efferent is the opposite of efferent, meaning 'away from the centre' and toward the periphery.
Course and Innervation
The pathway for fibers of the trochlear nerve is the following (from the initiation in the brain to the termination in the periphery):
- The nucleus of the trochlear nerve can be found in the inferior colliculus of the encephalic Tract (brainstem).
- It is the only nucleus which provides fibers to the nerve bundle known as the trochlear Nerve.
- It exits the skull through the superior orbital fissure.
- It innervates a singular eye muscle: the superior oblique muscle.
- This nerve motorically governs the abduction, depression and internal rotation of the eye.
The pathway for the fibers of the abducens nerve is the following (from the initiation in the brain to the termination in the periphery):
- The nucleus of the abducent nerve can be found in the facial colliculus of the brainstem.
- It exits the skull via the superior orbital fissure.
- It innervates the lateral rectus muscle of the eye.
- This nerve governs the muscle responsible for abduction (lateral movement) of the eye within the orbit.
Trochlear nerve: Inferior colliculus -> Superior orbital fissure -> Superior oblique muscle.
Function: Abduction, depression, internal rotation of the eye.
Abducens nerve: Facial colliculus -> Superior orbital fissure -> Lateral rectus muscle.
Function: Abduction (lateral movement) of the eye.