🥇 6to Par Craneal - NERVIO ABDUCENS (Oculomotor Externo). ¡Explicación Fácil y Sencilla!

Anatomy of the Sixth Cranial Nerve

In this section, the speaker introduces the topic of the sixth cranial nerve, also known as the abducens nerve, focusing on its origin and function within the anatomy of the eye.

Origin and Function of the Abducens Nerve

• The sixth cranial nerve is responsible for moving a single muscle in the eye, specifically one of the extraocular muscles.

• It is crucial to differentiate between real and apparent origins when discussing cranial nerves. The real origin refers to where neurons originate to transmit information through the nerve.

• The nucleus of the abducens nerve is primarily motor and located in the brainstem at a level slightly lower than that of the third and fourth cranial nerves.

• The abducens nucleus is situated within the pons, specifically within a structure called the facial colliculus, which plays a role in forming part of this structure.

• Apart from its real origin, the abducens nerve also has extranuclear connections such as corticonuclear fibers for voluntary control over skeletal muscles like those involved in eye movement.

Detailed Nerve Pathway Explanation

In this section, the speaker explains the pathway of a specific nerve in detail, highlighting its origins and relationships with surrounding structures.

Nerve Pathway Origins and Relationships

• The nerve abducens originates from the posterior cranial fossa, between the pons and medulla oblongata. It emerges at the cerebellopontine angle.

• Upon emerging, it traverses through the subarachnoid space and has close relations with the basilar artery, inferior cerebellar artery, and labyrinthine artery.

• The nerve ascends towards the globe of the eye by passing through the dura mater and reaching the petrous part of the temporal bone.

• As it progresses towards the superior orbital fissure, it interacts with structures like internal carotid artery and other ocular motor nerves.

Nerve Abducens Trajectory

This segment delves into how the nerve abducens relates spatially to other cranial nerves within the cavernous sinus.

Spatial Relations of Nerve Abducens

• The abducens nerve is positioned below and slightly lateral to the internal carotid artery within the cavernous sinus.

• It lies medial to ocular motor nerves while being lateral to trochlear (fourth cranial) nerve.

• Positioned above and lateral to abducens is ophthalmic nerve, a branch of trigeminal nerve.

• Medially located in relation to all these nerves is maxillary nerve, which runs inferiorly and laterally within this region.

Final Orbital Penetration

This part elucidates how the abducens nerve penetrates into orbit through specific anatomical structures.

Orbital Penetration Route

• Upon reaching superior orbital fissure, abducens must pass through annulus of Zinn along with ophthalmic veins.

• Once inside orbit, it targets lateral rectus muscle exclusively for innervation without branching off into collateral pathways.