Notes of Cranial Nerve: III, IV, VI.pptx

This is about cranial nerve III, IV, VI.

1. Cranial Nerve III, IV, VI Dr Sidra Ayub

2. OCULOMOTOR NERVE (III)

3. Introduction The oculomotor nerve is the third cranial nerve (CN III), and one instance in which the name is a clear indication of the function of the nerve ( Oculo = pertaining to the eye, motor = producing movement). Simply from the name then, it is easy to know that the oculomotor nerve will innervate muscles that move the eye itself or components of the eye. It is the movement producing functions of the nerve that make it a useful indicator of brain injury.

4. Origin The cell bodies of the oculomotor nerve are located within two nuclei positioned close to one another, posteromedially in the midbrain, the most superior component of the brainstem. The cell bodies and their somatic motor nerve fibers, or axons, that will innervate skeletal muscles associated with the eye, arise from the oculomotor nucleus. The cell bodies and their visceral motor nerve fibers, or axons, that innervate muscles within the eye itself, arise from the Edinger-Westphal nucleus.

5. Pathway and supply

6. Trochlear nerve (IV)

7. Introduction The trochlear nerve is the fourth paired cranial nerve (CN IV). Along with the oculomotor nerve (CN III) and the abducens nerve (CN VI), it is responsible for controlling movement of the eyeball. Interestingly, the trochlear nerve has the longest intracranial course despite being the smallest of all cranial nerves (by number of axons). The tendon of the muscle supplied by the trochlear nerve (superior oblique muscle) passes through a cartilaginous pulley-like structure known as the trochlea (Latin: trochlea = pulley), which grants the nerve its name.

8. Origin The trochlear nerve (CN IV) arises from the trochlear nucleus located within the periaqueductal gray substance of the midbrain and emerges on the dorsal midbrain caudal to the inferior colliculus. It then crosses the midline, before passing anteriorly around the contralateral side of the brainstem . Once curved around the midbrain, the trochlear nerve pierces the dura mater at the inferior margin of the tentorium cerebelli to run anteriorly within the lateral wall of the cavernous sinus. It then ultimately enters the orbit through the superior orbital fissure, external to the common tendinous ring ( Anulus of Zinn).

9. Pathway and supply

10. Abducent / abducens nerve (VI)

11. Introduction the abducens (or abducent ) nerve is the sixth paired cranial nerve (CN VI). Along with the oculomotor nerve (CN III) and the trochlear nerve (CN IV), it is a purely motor nerve responsible for controlling movement of the eyeball. Similar to oculomotor and trochlear nerves, the abducens nerve attributes its name to its function. It supplies the muscle (lateral rectus muscle) involved in abduction of the eye i.e. drawing the eye away from the midline.

12. Origin The abducens nerve (CN VI) arises from its associated nucleus (nucleus of abducens nerve) located beneath the floor of the fourth ventricle in the caudal pons. Nerve fibers pass anteriorly through the pons to emerge from the medullopontine sulcus at the junction between the pons and the pyramid of the medulla ( pontomedullary junction).

13. Pathway and supply The nerve then continues ventrally and pierces the dura mater covering the basilar part of the occipital bone . It reaches the superior margin of the petrous part of the temporal bone to enter the cavernous sinus, accompanying the internal carotid artery, the oculomotor nerve (CN III), trochlear nerve (CN IV) and the ophthalmic branch of the trigeminal nerve (CN V1) in their course. The abducens nerve concludes its path by exiting the cavernous sinus to enter the orbit via the superior orbital fissure and then pass through the common tendinous ring ( Anulus of Zinn)

14. Summary

15. Summary