Anatomy of trochlear nerve ophthalmology.pptx

Trochlear nerve anatomy

1. Anatomy of Trochlear Nerve Ritwik Raj 21770722

2. Trochlea comes from Latin word trochleae meaning a pully. In each eye the superior oblique muscle functions as pully and is innervated by the trochlear nerve. It is the only cranial nerve to arise from the dorsal aspect of brain. It is the only cranial nerve to completely cross from one side of the brain to another.

3. Functional Components Somatic efferent component is concerned with the movement of eye balls through the superior oblique muscle. General somatic afferent component carries proprioceptive impulse from the superior oblique muscle. These impulses are relayed to mesencephalic nucleus of trigeminal nerve.

4. Nucleus The trochlear nucleus is situated in the ventromedial part of the central grey matter of the midbrain at the level of inferior colliculus It is caudal to and continuous with the oculomotor nerve nucleus complex.

5. Connections of the nucleus

6. Course and distribution 3. Cavernous part 1. Fascicular part 2. Pre-cavernous part 4. Orbital part

7. The fascicular part It consists of efferent fibres that curve posteriorly around the aqueduct and decussate completely in the anterior medullary velum.

8. Pre-cavernous part or trunk The nerve leaves the brainstem on the dorsal surface, just caudal to inferior colliculus. It then curves laterally around the brainstem, runs forward beneath the free edge of the tentorium and like the 3 rd nerve, passes between the posterior cerebral artery and the superior cerebellar artery. It pierces the dura on the posterior corner of the roof of cavernous sinus and enters into it.

9. Intracavernous part In the cavernous sinus, it runs in the lateral wall of the sinus, inferiorly to the 3 rd nerve and above the first division of the 5 th nerve. In the anterior part of sinus, it rises and passes through the superior orbital fissure, above and lateral to the Annulus of Zinn.

10. Intraorbital part After entering the orbit through the lateral part of the superior orbital fissure, it passes medially above the origin of levator palpabrae superioris It ends by innervating the superior oblique muscle LPS

11. Clinical significance Lesion of the trochlear nerve causes paralysis of the superior oblique muscle of eyeball. This clinically presents with Extorsion of the eyeball and weakness of the downward gaze Diplopia

12. References The anatomy and physiology of the eye- Khurana and Khurana, 2 nd edition Kanski clinical ophthalmology, 6 th edition Gray’s anatomy, 42 nd edition THANK YOU