Nerve06/eyes and ears/introduction to Weber test
The vibrating tuning fork is placed on the center top of the (half donut-shaped) skull. By doing so, the vibration transmitted via the skull (shown by the striped-arrow) stimulate the (cone-shaped) cochlea in the inner ear. The inner ears generate (red-colored) action potentials, on the vestibulocochlear (VIIIth cranial) nerves. When these reach the cerebral cortex, auditory sensation is elicited.
In normal subjects, with no significant difference in the sensitivity of both inner ears, the amount of action potentials reaching the brain from both nerves is about the same. So, the sound does not shift right, nor left, and would be heard in the middle.
Challenge Quiz
When performed the Weber test, the subject said the sound was shifted to the left side. This is a normal.abnormal finding.