Mar 02 2008
Deafness
Since lecture was cancelled this week, I decided to post about lab. Our sense of hearing is the ability to detect mechanical vibrations we call sound. Deafness can be inherited or acquired.
Acquired Deafness:
If a labratory animal is exposed to very intense, pure tones, the animal eventually becomes deaf to those frequencies, but it’s ability to detect other frequencies are unimpaired. Examination of its organ Corti reveals destroyed hair cells in a single area whose location can be easily correlated with the pitch of destructive sound. Similar defecits occur in humans who are exposed to intense noises for long periods.
Inherited Deafness:
About 1 in 1000 newborns are born deaf because of a genetic defect. As the years go by, about 16% of humans suffer a progressive loss of hearing due to genetic defects. Mutations in a transcription factor have been associated with a stapes that cannot move freely and thus cannot transmit vibrations to the oval window. The proper organization of the stereocilia involves actin, a form of myosin and cadherins. Mutations in the gene encoding a protein that helps with actin polymerization also cause deafness. The potassium that enters the hair cells must be removed from them and recycled back to the endolymph for hearing to continue. Failure for the process to happen is linked to deafness.
*Interesting Facts*
-deaf people have safer driving records than hearing people nationally!
-when Beethoven produced his 9th symphony, he was profoundly deaf
-about 22 million people in the U.S. are hearing impaired
-the man who invented shorthand, John Gregg, was deaf
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