Bone conduction: an explanation for this phenomenon comprising complex mechanisms.

Bone conduction hearing inevitably involves vibration of the basilar membrane in response to a pressure gradient on either side of the membrane. The propagated wave that symbolizes this vibration of the basilar membrane can be triggered intentionally, when a bone vibrator is placed on the mastoid bone, or inadvertently when testing hearing of one ear by air conduction while disregarding transmission of the sound to the other side. When hearing is tested with a bone vibrator, the pathways leading to the basilar membrane can be divided into two main categories. The first type of pathway short-circuits the middle ear and comprises three distinct mechanisms: cochlear fluid inertia, compression of the cochlear walls, and pressure changes exerted via cerebrospinal fluid. In the second type of pathway, the stimulus reaches the basilar membrane via the middle ear, either directly or via the outer ear. Although it is difficult to precisely determine the contribution of each of these pathways to the basilar membrane, bone conduction remains the clinically most reliable way of directly testing cochlear function.