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.
Key Points. 1  Cranial nerve XI is responsible for tilting and rotating the head, elevating the shoulders, and adducting the scapula. 2  Most of the fibers of the accessory nerve originate in neurons situated in the upper spinal cord. 3  Due to its unusual course, the accessory nerve is the only nerve that enters and exits the skull.