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Cranial nerve VIII - the Acoustic nerve

There are two separate parts of the acoustic nerve known as the cochlear and vestibular nerves.

 

Signs and Symptoms of Lesions

Cochlear involvement – In the early signs of peripheral cochlear disease, the individual has a ringing, buzzing, hissing, singing or roaring noise in the ear. The interruption of the nerve path causes nerve deafness and/or tone deafness with the ability to hear but not comprehend.

Vestibular involvement – Includes dizziness, rapid involuntary eye movement, diaphoresis, tachycardia, nausea, vomiting and low blood pressure.

 

Acoustic Nerve Test

Cochlear:

With the individual seated, the practitioner stands behind and rubs their thumb and index finger together, in a way that a low-level sound is emitted.  Dependent upon the distance from the ear that this sound is heard may signify hearing loss.



Acoustic nerve test

A more specific test may be accomplished through the use of a tuning fork, which has a capability of 256 Hz.  After striking the fork, the base is placed on the mastoid process, and then the fork is moved off the mastoid to the front of the ear, then to the back.  The ability to perceive sound is greater from the front than the rear.

Should the individual be unable to hear the tuning fork when placed on the mastoid, the practitioner should consider nerve deafness.  If the vibration is heard on the mastoid but not observed when placed to the front or the rear of the ear, middle ear disease is a consideration.

If hearing loss is only experienced on one side, strike the tuning fork again and place the base on the bridge of the nose and the mid-vertex of the scalp.  Individuals with middle ear disorders will be able to hear this sound in the affected ear.

Vestibular:

Observe the individual's gait for ataxia and perform the Romberg’s test.

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