Human Cranial nerves are a set of 12 paired nerves that come directly from the brain. The first two (olfactory and optic) come from the cerebrum, with the remaining ten come from the brain stem. The names of the these nerves relate to what function they perform and are also numerically identified in roman numerals (I-XII). The nerves serve in functions of smell, sight, eye movement, and feeling in the face. These nerves also control balance, hearing, and swallowing.
As with all nerves, symptoms describe the location of the lesion
Lesion in the lingual nerve will result in loss of taste, general sensation in tongue & salivary secretion
Lesion proximal to the branching of the chorda tympani such as in the facial canal will result in the same symptoms without the loss of general sensation of the tongue (because V3 has not yet joined the CN VII)
Corticobulbar innervation is asymmetric to the upper and lower parts of the Facial Motor Nucleus
If there is an UMN lesion (lesion to the corticobulbar fibers) the patient will have paralysis of the muscles of facial expression in the contralateral lower quadrant
If there is a LMN lesion (lesion to the facial nerve itself) the patient will have paralysis of the muscles of facial expression in the ipsilateral half of the face
Testing Cranial Nerve CN VII
Ask the patient to mimic you or follow instructions to make certain facial expressions
Be sure to assess all four quadrants of the face
Close eyes tightly
Check for strength of the buccinator muscle against resistance
Ask patient to hold air in their cheeks as you press gently from the outside
Patient should be able to hold air in against resistance
Cranial Nerve VIII – Vestibulocochlear
Cranial Nerve VIII Clinically
Changes in hearing alone are most often due to
Infections (otitis media)
The most common lesion to this nerve is caused by an acoustic neuroma
This affects CN VII and CNVIII (cochlear AND vestibular divisions) due to proximity in the internal auditory meatus
Symptoms include nausea, vomiting, dizziness, hearing loss, tinnitus, and bell’s palsy etc.
Testing Cranial Nerve CN VIII
Can the patient hear equally on both sides?
Tests for lateralization
256 Hz tuning fork placed on top of the patient’s head in the center, is it louder on one side than the other?
Compares air conduction to bone conduction
Normally, air conduction should last 1.5-2 as long as bone conduction
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