Definition of COUNTERBORE. : to form a counterbore in: enlarge (part of a hole) by means of a counterbore.ADVERTISEMENT.efinition of COUNTERBORE. 1. : a flat-bottomed enlargement of the mouth of a cylindrical bore. 2. : a drill for making a counterbore â compare countersink.
The vestibulocochlear nerve (auditory vestibular nerve) , known as the eighth cranial nerve, transmits sound and equilibrium (balance) information from the inner ear to the brain.
Aminoglycosides can cause eighth cranial nerve damage, resulting in vestibular and/or auditory toxicities. Symptoms include dizziness, nystagmus, vertigo, ataxia, tinnitus, and varying degrees of hearing impairment.