This complex set up allows for small air pressure changes (sound) distributed over the relatively large surface area of the eardrum to be concentrated at the oval window with an increase in vibratory intensity. Herein lies the problem with gunshots. Gunshots generate intense air pressure waves (sounds) and when concentrated, can result in far too much mechanical vibration for the cochlea to safely and repeatedly handle.
The cochlea is a very fascinating organ. It's curled like a snail shell in appearance. There are three chambers that transverse the length of the cochlea. The complexity of this system is extraordinary even when compared to our other senses. To simplify, all the action takes place in the middle chamber known as the scala media. Along the floor of the scala media is a complex of hair cells and support tissue collectively known as the organ of Corti.
The phonograph is perhaps the best analogy for what happens to convert vibration into electrical nerve impulses that we interpret as sound. A phonograph needle is mechanically moved through a magnet by the uneven surface of the vinyl record and that creates an electrical impulse, which creates sound when it's amplified and that in turn drives a membrane into motion (the speaker). The alterations in electrical frequency correspond to different sounds. Hence a range of sound can be recorded on a phonograph record that extends beyond what we can normally hear at both the high and low end of our sound spectrum.
At the oval window of the cochlea, the footplate of the stirrup sets up mechanical vibrations that pass through to the scala media and hence the hair cells. These hair cells act in a fashion analogous to the phonograph needle as they are the ultimate transducers of mechanical action into electricity (nerve impulses). These nerve impulses are sent directly to the brain where we experience them as sound. Vibrations of a high pitch are perceived very close to the oval window and vibrations of low pitch are perceived at the far end of the cochlea.
Getting back to gunshots and away from biology class, loudness is not related to pitch. The loudness of a tone appears to depend on the number and intensity of the hair cells set into motion by the mechanical stimulation of the eardrum and its bony amplification system. In a simple model, the more intense the air pressure wave (sound) the more intense the vibrations received at the oval window and the more violent the vibration of the organ of Corti. In essence that is how our hearing breaks down, either gradually or even with a single extra violent shaking.
Normal aging (our constant companion) results in a deterioration of this complex function. High-pitched sounds are lost first. This is known as Presbyacusis. The extent of this “normal loss” is of course highly variable and depends on an individuals, genetics, history of ear infection, trauma and as we are increasingly finding out, nutrition.
More pathologic hearing loss can be divided into two categories. Conduction hearing loss is due to malfunction in the eardrum and its bony partners. For shooters the much more common “nerve deafness” begins to play out. This occurs most commonly from damage to the organ of Corti and its closely linked nerve pathways, usually from mechanical vibratory trauma (the much desired boom). Clearly then a target shooter or avid bird shooter is at higher risk then say, the whitetail hunter simply on the basis of the number of shots fired.
