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From: Wayne.Roorda@p0.f14.n385.z1.fidonet.org (Wayne Roorda)
Newsgroups: misc.handicap
Subject: Noise damage hearing loss
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Date: 21 Dec 90 05:12:26 GMT
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Index Number: 12540

[This is from the Silent Talk Conference]

In the November 1989 issue of DISCOVER Magazine, in the Up Front 
section on page 18 there is a column titled "Bad Vibes". 
 
Hearing specialists have long stressed the dangers of rock concerts, 
but it's not the moral fiber of America's youth they're worried about. 
What concerns them are the fine, upstanding tufts of hair that stick 
up from the sensory cells of the inner ear.  When exposed to 
prolonged, intense sound, these hairs can flop over like stalks of 
wheat pummeled by hail.  Until recently, however, no one knew exactly 
why they collapsed. 
 
Using an electron microscope, Harvard physiologist Charles Liberman 
examined the sensory hairs of cats that had sustained mild but 
potentially reversible hearing loss, then compared them with the 
sensory hairs of cats with permanent hearing loss.  "With temporary 
loss, you can't see a heck of a lot wrong with the hair cells," 
Liberman says.  But in the permanently deaf cats the hairs had keeled 
over.  The hairs' rootlets - the small, narrow structures connecting 
them to the rest of the cell - were broken. 
 
Liberman thinks of the damage to the rootlets much like a stress 
fracture.  When sounds enters the ear, he explains, the hairs rock 
back and forth in response to the resultant vibrations.  The rocking 
causes the sensory cells to release a neurotransmitter that stimulates 
auditory nerves, leading to the sensation of sound in the brain.  The 
hairs themselves, however, are ridgid; they can bend only at the 
flexible rootlet.  If the rootlet is overstressed, forced to rock too 
hard and too long, it can eventually break.  With the collapse of the 
sensory hairs, the whole cell becomes useless, as does its associated 
nerve, and some hearing is lost forever. 
 
"From a mechanical point of view, it makes intuitive sense that this 
pivotal point is the weak link," says Liberman.  And, although there's 
no proof yet, he has a theory for why that link finally snaps. 
 
"Constant rocking takes energy," he says.  Moreover, it causes wear 
and tear on the rootlet, and repairs take energy, too.  "If the 
intense motion goes on for too long," Liberman speculates, "maybe the 
cell simply runs out of gas." 
 
 
I copied this in hopes that we will get some feedback and or 
discussion started from the hearing healthcare professionals and 
"Silent Reader's" who may be reading this conference and not 
posting.  And everyone else let's hear from you too.  BTW I've 
cross-posted this to the ABLED echo too. 

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