Starting this post was the hardest for me, because I didn't know what to begin with, but I guess giving you a snippet of my previous post, on the Cranial Nerve Series. If you haven't read these posts, then you are missing out. You can go through the snippet, and click on the links to read the posts individually.
The Olfactory Nerve (cranial nerve 1) is responsible for Smell, where the Olfactory receptor neuron takes the odor particle which is trapped in the mucus line to into glomerulus in the olfactory bulb, where neurotransmitter are sent to the Mitral cells. Not forgetting GABA, which is produced by granule cells in the glomerulus to help regulate the odor that gets in (so you do not keep perceiving different odor randomly which aren't necessary) - Neurology Explained - The Olfactory nerve (Cranial Nerve 1)
The Cranial Nerve II is a special sensory afferent nerve fiber that originates from the retina, as light rays are received by the Retina. The nerve picks information from the photoreceptors (Rods, Cones and the ganglion cells), to allow for visions. It is important to know that the Cranial Nerve II is a sensory nerve. - Neurology Explained - The Optic nerve (Cranial Nerve 2)
The third cranial nerve originates from the Midbrain, at the level of the superior colliculus, which is moved with the General somatic efferent fibers, and the Parasympathetic nerve fiber (GVE). It is responsible for supplying the majority of the eye muscles, which I listed above, and the Third cranial nerve is responsible for the eye and eyelid movement.Neurology Explained - The Oculomotor nerve (The Cranial Nerve 3)
The troclear nerve nucleus is located at the level of the inferior colliculus, within the midbrain. Each nucleus crosses one another to feed the oppsite eyeballs (meaning that the left trochlear nerve necleus innervate the righ superior oblique, therby affecting the right eyeball, while the right trochlear nerve nucleus innervates the left superior oblique, affecting the left eyeball). - Neurology Explained - The Trochlear Nerve (The Fourth Cranial Nerve)
The trigeminal nerve has its origen in the Brain stem, with Spinal Trigeminal nucleus, central/principal pontine trigeminal nucleus, mesencephalic trigeminal nucleus, and the trigeminal motor nucleus. It supplies a lot of structures including the palpebral, skin of the scalp in the temporal, forehead, the pinna of the ear, the jaw, the teeth, the chin skin, the external part of the nose, the nasal cavity, the oral cavity, and many more areas of the face, and muscles of mastication (chewing) which includes (the Tensor Tympani and the tensoe veli palatini). - Neurology Explained - The Trigeminal Nerve (The Fifth Cranial Nerve)
I guess I have been able to overcome my beginning fright, and at the same time, I have been able to say Hello. Today, I will be discussing the sixth cranial nerve (the Abducens Nerve), so without any further ado, I will see you at the end of the post.
Similar to the fourth and the fifth cranial nerve, the abducens nerve has its origin in the mid-brain. The nucleus of the abducens nerve is located at the level of the facial colliculus, around the fourth ventricle which is connected to the cerebral aqueduct which transmit cerebrospinal fluid into the spinal canal, within the pons of the mid-brain. To further explain the location of the nucleus of the 6th cranial nerve, it is located slightly above the 7th cranial nerve nucleus (facial nerve), and its motor fibers loop over the 6th cranial nerve through the facial colliculus, towards the pontomedullary junction, while nerve of the abducens nerve nucleus moves downwards towards the same pontomedullary junction. (To be clear, it isn't only Cranial nerve 6 and 7 that comes out of the pontomedullary junction, Cranial nerve 8 (vestibulocochlear nerve) also comes out there)..
Outside the pontomedullary junction, the 6th cranial nerve runs below the pontine branches and above the anterior inferior cerebellar artery, to get into the Dorello’s canal along with the inferior petrosal sinus, then get into the petrous temporal bone, then to the cavernous sinus.. The abducens nerve runs within the cavity of the cavernous sinus, and it runs through the internal carotid artery in the cavernous sinus to the end of the cavernous sinus, after which it goes to the superior orbital fissure where it moves into the orbital cavity where it supplies the lateral rectus muscle. Do you remember in my previous post, where I explained that in the eye, the Superior Oblique is innervated by the 4th cranial nerve, The lateral rectus muscle is innervated by the 6th cranial nerve, while all other muscles are innervated by the 3rd cranial nerve? It is important to know that the abducens nerve is found inside the common tendinous ring. The common tendinous ring, also known as the annulus of Zinn, or annular tendon, is the fibrous tissue ring surrounding the optic nerve. It is an origin for six optical extraocular muscles. On the superior side is the superior rectus. Medially and Superior to superior rectus is the levator palpebrae superioris, and medial to the levator palpebrae is the superior oblique muscle. The Superior rectus is attached to the Dura mater. To the medial side of the ring is the Medial Rectus, looping laterally and inferior of the annulus of Zinn is the lateral rectus, at a 23° angle, of the annulus of zinn, is the inferior rectus. There is a neurovascular structures/tubercle on the greater wing which inserts into the annulus of zinn. In the tubercle of the oculomotor nerve, inside the annulus of zinn is located, the inferior branch of the oculomotor nerve, the Nasociliary Nerve, the superior branch of the oculomotor nerve, as well as the 6th cranial nerve. Outside the Annullus of zinn, but in the neurovascular structures/tubercle are the lacrimal nerve, frontal nerve, and trochlear nerve. .
The Abducens nerve is responsible for causing the lateral rectus to contract, causing the abduction (lateral rotation) of the eyes.. In cases where there are obstructions infarction, or abscess, or multiple sclerosis, which will affecting the abducens nerve, or any other clinical condition affecting the abducens nerve could lead to a cranial nerve 6 palsy. Trauma leading to fracture could damage bones along the nerve pathway leading to nerve damage which would cause the eyeball to go to the middle and to bulge outward when needed. If the right abducens nerve is destroyed, the eyeball goes inward known as right Unilateral strabismus.,
Conclusion
The abducens nerve is a motor nerve that has its origin in the inferior pons, close to the facial colliculus. The abducens nerve supplies the lateral rectus in the orbital cavity, using General Somatic fibers for eye movement (abduction or the lateral rotation of the eye).