The Ophthalmic, Maxillary and Mandibular divisions of the Trigeminal nerve (i.e. the fifth cranial nerve or CN V) are the source for somatic sensation over the entire face, the eyes, the nasal passages and the oral cavity. Typically CN V lesions cause pain and do NOT manifest clinically with facial deviations of any kind at rest. Symptoms of damage to the trigeminal system are mainly loss of sensation in the face (although the mandibular division of the trigeminal nerve also controls jaw motion).
Damage to the facial nerve (i.e. seventh cranial nerve or CN VII) on the other hand, mainly manifests as weakness of the muscles of facial expression (although it may also affect taste sensation in the anterior part of the tongue).
The jaw-jerk reflex is lost in CN V damage. In addition, because of weakness of both the temporalis and masseter muscles (i.e. muscles of mastication) and the medial pterygoid muscle which closes the jaw and moves it from side-to-side (grinding motion), the jaw deviates toward the weak side on opening.
One of the most common example of trigeminal nerve dysfunction is trigeminal neuralgia (tic douloureux), an irritation of the nerve that probably occurs due to contact with anomalous intracranial blood vessels. This process causes severe paroxysms of pain in one or more divisions of the trigeminal nerve, with the maxillary division being most often affected and the ophthalmic least.
The most common cause of facial weakness is Bell’s palsy, an idiopathic condition that may result from viral infection-induced inflammatory swelling of the facial nerve in its canal. Since the canal is very long and tight, swelling can put pressure on the nerve, resulting in damage either by direct effects or by impairing blood flow in the nerve.
The hallmark of peripheral facial nerve palsy (CN VII) is that it involves the entire side of the face, including weakness of the forehead muscles as well as those around the eye and mouth. This is because fibers to all of these regions of the face are packed together in the facial canal.
The most prominent deficit noted by patients with facial nerve damage is weakness of muscles of facial expression. Careful observation of the patient’s face during conversation and at rest almost always reveals facial weakness. Additionally, the face may “droop” on the side of damage due to the effects of gravity. The nerve can be further tested by: having the patient close their eyes and lips tightly (the force of closure can be felt by manually trying to open them); having the patient grimace (show their teeth); having the patient look up (elevating the eyebrows and creasing the forehead); and also having the patient fill their cheeks with air with their lips tightly pursed. If one or both sides of the face are weak, s/he will have difficulty holding the air in. Tapping each cheek accentuates the difficulty on the appropriate side. Most cases of uncomplicated Bell’s palsy recover quite well.
0
0