MadSci Network: General Biology

Re: Whenever I wish too I can make a 'rumbling noise' in my head..

Date: Tue Sep 14 08:28:00 1999
Posted By: Gerald Popelka, Faculty, Occupational Therapy, Washington University
Area of science: General Biology
ID: 937027623.Gb

I agree with your ex-physician but will try to give an explanation.

The eardrum is connected to a series of bones in the middle ear.  This 
series of bones acts like a lever system to conduct sound from the ear drum 
to the inner ear where the sensation of hearing actually occurs.  The 
neural structures in the inner ear can be permanently damaged by exposure 
to high level sounds.  There are two small muscles in the middle ear behind 
our eardrums that are connected to this series of bones.  One muscle is the 
tensor tympani and the other is the stapedius, the smallest muscle in our 
body.  These two muscles contract involuntarily in the presence of various 
stimuli including high levels of sound in the case of the stapedius, and 
very high levels of sound in the case of the tensor tympani.

For low level and moderate level sounds, up to about 90 dB sound pressure 
level, these muscles show no activity.  For sounds greater than 90 dB, the 
stapedius muscle begins to contract involuntarily and contracts harder for 
sounds that are louder.  At very high sound levels, around 120 dB or so, 
the tensor tympani contracts.  When the muscles contract, they reduce the 
sound vibrations going through the series of bones which has the effect of 
reducing or damping the sound reaching the inner ear.  Therefore, the most 
common explanation of the function of these involuntary muscle contractions 
is that they automatically protect the inner from loud sounds.  Another 
explanation for these muscle contractions, particularly for the stapedius 
muscle, is that they automatically allow fine adjustments of the tension of 
the ear drum to optimize sound transmission.  In either case, the 
contractions are involuntary and operate automatically without us being 
aware of them.

Individuals in a small percentage of the population can contract these 
muscles voluntarily even though the muscles normally contract only 
involuntarily.  The voluntary contraction of these muscles causes them to 
vibrate not unlike the small vibrations in any muscle that is contracted 
very hard, say the muscles in your arm.  You perceive these contracted 
middle ear muscle vibrations as a "rumbling noise" because the vibrations 
are transmitted the middle ear bones and then to the inner ear.  I suspect 
that you are among this small percentage of the population who can 
voluntarily contract the middle ear muscles.

Why can't you hear the "rumbling noise" when the muscles contract 
involuntarily?  First, the loud sounds that cause the involuntary muscle 
contractions are much louder than the quieter "rumbling noise" from the 
muscle contractions making the "rumbling noise" inaudible.  Second, the 
involuntary muscle contractions are probably much weaker than voluntary 

You might be aware that a small percentage of the population can wiggle 
their external ears, the part of the ear on the side of the head.  The 
muscles that contract to wiggle the ears also are activated involuntarily.  
This function is easily observed in a dog for example, when it 
automatically moves its ears to help determine from where a sound is 
coming.  Even though this involuntary function has largely disappeared in 
humans, a small percentage of us still can voluntarily wiggle our ears.  
So, a few people can voluntarily contract any of the muscles of the ear 
though this ability has no particular usefulness nor does i

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