http://hyperphysics.phy-astr.gsu.edu/HBASE/sound/protect.html
Interesting website...
Apparently the ear does have some built in protection mechanisms against loud sounds. The website does state clearly that the protection mechanism is not effective against abrupt sounds, but I wonder how well that statement applies if the person is
expecting an abrupt sound.
In response to sustained loud sounds, muscle tension tightens the tympanic membrane and, acting through the tendon connecting the hammer and anvil, repositions the ossicles to pull the stirrup back, lessening the transfer of force to the oval window of the inner ear. This contributes to the ear's wide dynamic range.
In response to loud sounds, the tensor tympani muscle tightens the eardrum and through the tendon between the hammer and anvil and shifts the stirrup backward from the oval window of the inner ear. This shifting of the ossicles reduces the transmitted force to the inner ear, protecting it. However, it is a relatively slow action and cannot protect the ear from sudden loud sounds like a gunshot. The process is less effective in older ears.
A young person's ear can provide a limited amount of protection from sustained loud sounds by shifting the stirrup backward so that it doesn't exert as much force on the oval window. In the very young, the stirrup is thought to be capable of actually breaking contact with the oval window, breaking the direct link to the inner ear. In an older ear, the structures become stiffer and cannot adjust backward as much. Older persons are generally less tolerant of loud sounds.
Another website with similar comments.
http://www.neurophys.wisc.edu/h&b/textbook/mid_ear.html
Again they say that this is only to protect against sustained loud sound, but they do not address the possibility that foreknowledge of the shot (particularly in a very high stress situation) might have a similar effect.
The tensor tympani and stapedius tensor muscles in the middle ear contract reflexly in response to loud sounds. Both muscles increase the stiffness of the ossicular chain when they contract and thus reduce sound transmission by up to 15 dB, depending on frequency. In humans the stapedius tensor is much more effective than the tensor tympani. The reflexes are generally thought to be primarily a protective mechanism to shield the inner ear from damage due to intense sound but, because the latency of contraction is at least 10 milliseconds, they cannot protect against impulsive sounds such as a pistol shot. Since the reflexes primarily reduce the transmission of low frequencies, they also act to improve the discrimination of speech sounds in the presence of loud, low frequency background noise.
Ah HAH!
This article mentions the possibility that these protective mechanisms can be activated by stress!
They're talking about a specific kind of tinnitus resulting from rhythmic contractions of the muscles that provide the protective mechanism, but it's an interesting connection between the actions of these muscles and stress/anxiety.
http://www.umm.edu/otolaryngology/tinnitus2.html
There are two muscles within the middle ear attached to the middle ear bones. These are the stapedius, attached to the stapes, and the tensor tympani, attached to the malleus. Normally, these muscles function as a protective mechanism against loud sound. When the muscle begins to spontaneously contract, it usually does so in a rhythmic pattern and gives the impression of a repetitive clicking or fluttering sound. Although it is annoying, this type of tinnitus is not dangerous, is often brief, and usually resolves without treatment.
The palate muscles and muscles of the eustachian tube (the cartilaginous and bony organ between the middle ear and back of the throat) are additional sources of myoclonic and spastic activity which can be heard in the ear. A patient may observe myclonus in the palate by opening the mouth and watching the palate vibrate.
What causes myoclonus is unclear. The muscles of the ear, eustachian tube, and palate are subject to the same forces that cause muscle spasm in any other muscle of the body including stress and anxiety. Often there is not apparent reason.
Found this article regarding the "Hearing Pill" mentioned earlier while I was poking around on the web.
http://www.asha.org/about/publications/leader-online/archives/2005/050614/050614e.htmA recently concluded double-blinded, placebo-controlled clinical trial reviewed use of a commonly available nutritional supplement, N-acetylcysteine or NAC. The study by the Naval Medical Center San Diego at the Marine Corp Recruit Depot in Camp Pendleton, CA, used a special formulation of NAC to determine its prophylactic qualities to prevent hearing loss.
The clinical trial found that when compared to the placebo, NAC reduced permanent hearing loss in the ear closest to the source of acoustic trauma. NAC also shows potential in healing symptoms of acoustic trauma, such as tinnitus and balance disorders. Another study will tackle those issues.
This isn't really what I was referring to in my earlier post. I had heard that steroid treatments administered soon after an exposure to damaging noise could ameliorate the damage.
