pinpoints the location of sound by differences in the timing of neuronal firing

Pinpoints the location of sound by differences in the

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pinpoints the location of sound by differences in the timing of neuronal firing patterns external auditory meatus (ear canal) oentrance is guarded by fine hairs oskin lining the canal contains modified sweat glands that produce cerumen (earwax) = traps fine foreign particles hairs and earwax help prevent airborne particles fromreaching the inner ear canal where they could accumulate or injure the tympanic membrane and interfere with hearing tympatic membrane (eardrum) -the tympanic membrane stretch across the entrance to the middle ear vibrates when struck by sound waves alternating higher and lower pressure regions of sound wave causes exquisitely sensitive eardrum to bow inward and outward in unison with wave’s frequency for membrane to be free to move as sound waves strike it resting air pressure on both sides must be equal outside of eardrum is exposed to atmospheric pressure that reaches it through theear canal inside of eardrum facing the middle ear cavity is also exposed to atmospheric pressure via the Eustachian (auditory) tube connects middle ear to pharynx normally closed but can be pulled open by yawning, chewing, and swallowing opening permits air pressure within the middle ear to equilibrate with atmospheric pressure so that pressures on both sides of TM are equal during rapid external pressure changes (during flight) eardrums bulges painfully as the pressure outside the ear changes while the pressure inside the middle ear remains unchanged opening by yawning allows the pressure on both sides of the TM to equalize relieving the pressure distortion as eardrum pops back into place -middle ear bones transfers the vibratory movements of TM to the fluid of the inner ear transfer is facilitated by a moveable chain of 3 small bones (ossicles) malleus attached to the TMincus stapes attached to oval window (entrance to fluid filled cochlea) as TM vibrates in response to sound waves chain of bones is set into motion at the same frequency transmitting this frequency of movement from TM to oval window resulting pressure on the oval window with each vibration produces wave like movements in the inner ear at the same frequency as the OG sound waves ossicular system amplifies the pressure of the airborne sound waves by 2 mechanisms to set up fluid vibrations in the cochlea pressure is increased as force exerted on TM is convey by the ossicles to the oval window because the surface area of TM is much larger than that of oval windowlever action of ossicles provides an additional mechanical advantage
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several tiny muscles in the more than middle ear contract reflexively in response to loud sounds (more than 70 dB) causing the TM to tighten and limiting movement of the ossicular chain reduced movement of middle ear diminishes the transmission of loud sound waves to inner ear to protect the delicate sensory apparatus from damage
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