Trigeminal nerve
Introduction
The trigeminal nerve is part of the nervous system responsible for transmitting pain, touch, and heat sensors from your face to your brain. It is a large, three-dimensional sensor in your head that provides hearing. One part called the mandibular nerve involves the motor function to help you chew and swallow.
The trigeminal nerve, also called the 5th cranial nerve, of the 12 cranial nerves.
There are two trigeminal nerves, one on each side of the head. They start in your brain and go all over the head.
Anatomy
Like a tree growing from your brain all over your face, the trigeminal nerve has roots and branches:
The trigeminal nerve begins between four nuclei - or groups of nerve cells - in your brain. Three of these nuclei control the activity of your senses. The fourth controls the operation of the vehicle (or your movement).
These three nerve nuclei combine to form a single nerve root near the nucleus, which is a large, central part of your brain stem.
This nerve root becomes a trigeminal ganglion as it leaves the brain stem on each side. (A ganglion is the collection of nerves outside the nervous system.) Each trigeminal ganglion is located near your temple next to your head, in front of your ear.
The trigeminal ganglion divides into three branches of the trigeminal nerve. These branches run on each side of your head in different parts of your face.
The branches of the trigeminal nerve>
The trigeminal nerve has three branches that perform different functions:
Ophthalmic: This branch sends nerves from the upper part of your face and your head to your brain. Ophthalmic refers to the eye. The ophthalmic nerve is related to your eyes, upper eyelids and forehead.
Maxillary: This nerve branch is responsible for the nerves in the middle part of your face. Maxillary refers to the upper jaw. The maxillary nerves extend to the cheeks, nose, lower eyelids and upper lip and gums.
Mandibular: The mandibular (lower jaw) is a branch of hearing aids in the lower part of your face, such as the jaw, lower lip and gums. These sensors also have motor functions. They help you to bite, chew and swallow.
Prominent distribution
Sensory-to-face, cornea, sinuses, nasal mucosa, teeth and anterior two third of tongue.
Motor to muscles of mastication
Etiology (damage)
Cerebrovascular accidents
Space occupying lesion
Fracture base of skull
Tabes dorsalis
Trigeminal neuralgia: Unknown etiology
Precipitating factors
Cold wind blowing on face
Washing the face with very cold water
Chewing or even talking
Symptoms/Signs
- Commonly affects elderly people
- Pain comes in paroxysms
- Lancinating and confined to distribution of nerve
- Each paroxysm lasts for a few seconds but may be followed by a dull ache.
- There may be spasm of facial muscle
- The pain may recur
- Flushing of face, dilatation of pupil, excessive lacrimation, secretion of nasal mucus and saliva on the side of pain
Differential diagnosis
- Disseminated sclerosis, young persons affected
- Basilar aneurysm
- Pain due to aural infection, toothache, temporomandibular arthralgia
- Herpes zoster, post herpetic neuralgia
- Cerebral tumors
Abducens nerve
Introduction
It is the 6th cranial nerve of the 12 cranial nerves.
Anatomy
The sensor can be divided into four distinct parts: the nucleus, the cisternal part, the cavernous sinus section, and the orbital part. The nucleus of the abducens resides in the dorsal pons, ventral to the bottom of the fourth ventricle, and is located only on the medial longitudinal fasciculus. About 40% of the axon project through the ipsilateral medial longitudinal fasciculus jumps to the contralateral medial rectus subnucleus to ultimately block the contralateral medial rectus muscles. The nucleus of the abducens is supplied by the pontine branches of the basilar artery.
In all cranial nerves, the abducens nerve has a second, longer intracranial course. It is found in the pores below the fourth ventricle, at the same level as the facial colliculus. In fact, the axons of the facial nerve loop surround the posterior aspect of the abducens' nucleus. This will be important for the clinic later. The nerve originates in the caudal, dorsal pontine below the fourth ventricle. After the fibers release from the nucleus, it moves up and forward before multiple axons leave the brain at the junction of the pontine and the medulla (i.e., pontomedullary groove) caudal and medial in both the facial nerve and the vestibulocochlear nerve areas.
The muscle then travels to the subarachnoid space and passes over the upper edge of the soft part of the temporal bone toward the clivus inside a fibrous sheath called Dorello's canal and enters the dura below the posterior clinoid process. Because it adheres to Dorello's trenches, the nerve tends to stretch as intracranial pressure rises, for a number of reasons discussed later. It then enters the cavernous sinus (along with the oculomotor nerve, trochlear nerve, and the first branch of the trigeminal nerve (V1), following the lateral vein in the carotid artery and medial to the anterior sinus wall, following a sphenoidal fissure.
Because of the neuroanatomy of the abducens nucleus and its proximity to the facial colliculus, infarcts affecting the dorsal pons can produce ipsilateral facial palsy and lateral rectus palsy.
Similarly, infarcts of the ventral pons can affect the abducens nerve fibers as they exit at the junction of the pontomedullary near the corticospinal tract. This produces antagonistic hemiparesis (remember that the corticospinal tract fibers fall to the level of the medulla).
Wernicke-Korsakoff syndrome (WKS) is another disorder associated with abducens nerve palsy. It is often associated with thiamine deficiency due to alcohol abuse. Older triad patients present with confusion, ophthalmoplegia, and ataxia. Ophthalmoplegia is caused by degeneration of the fourth ventricle, as well as other brain regions (mamillary bodies, thalamus, periaqueductal gray, walls of the third ventricle, cerebellum, and frontal lobe). As mentioned above, this can affect the abducens nerve fibers and cause horizontal nystagmus.
Muscles supplied: Lateral rectus muscle of the eye
Etiology (damage)
Pressure by aneurysm over cavernous sinus
Damage cause
Downward displacement of the brain stem due to raised intra cranial pressure
Diplopia
Convergent strabismus
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