Cranial Nerve Series: The Abducent Nerve (6th Cranial Nerve)
Overview
- The abducent nerve (6th cranial nerve) is a purely motor nerve.
- It supplies the lateral rectus muscle, which is involved in the abduction of the eye.
Pathway of the Abducent Nerve
- Nucleus Location: In the pons.
- Course: Travels through the medullopontine sulcus (junction between medulla and pons).
- Pierces Dura Mater: Travels through the cavernous sinus.
- Exits Cavernous Sinus: Enters the orbit via the superior orbital fissure.
- Innervation: Passes through the common tendinous ring to innervate the lateral rectus muscle.
Function
- Activation of the lateral rectus muscle causes the eye to move outwards (abduction).
Coordination of Eye Movements
- Hering's Law of Equal Innervation: Ensures balanced eye movements to prevent double vision.
- Right abducent nucleus activates the lateral rectus of the right eye, while the left abducent nucleus quiets down.
- Medial Longitudinal Fasciculus: Connects eye movement centers in the brainstem to align movements and prevent diplopia (double vision).
Neuroanatomy Details
- Brainstem Components: Medulla oblongata, cerebellum, pons, mesencephalon, and diencephalon.
- Rhomboid Fossa: Key location for cranial nerve nuclei.
- External Structures: Median sulcus, medial eminence, medulla ristraea, and facial colliculus.
Importance of Facial Colliculus
- Formed by the looping of facial nerve fibers around the abducent nerve nucleus.
- Located on the posterior side of the pons.
Clinical Relevance
- Compression of the Abducent Nerve: Can be caused by lesions or increased intracranial pressure.
- Symptoms of Compression: Paralysis of the lateral rectus muscle, leading to medial deviation of the affected eye and inability to abduct the eye.
Conclusion
- The abducent nerve is crucial for lateral movement of the eye and coordinated eye movements.
- Next video will cover the 7th cranial nerve (facial nerve).
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