A coiled trumpet-shaped fluid-filled organ {inner ear} {cochlea}|, 4 mm diameter and 35 mm long, is in temporal bone.
Inner ear, nearer auditory nerve, has one straight row of 3500 inner hair cells {hair cell, cochlea} and has three S-curved rows with 3500 outer hair cells each (10,500 total). Outer-hair-cell cilia poke through tectorial membrane. Hairs have long part, medium part, and short part, linked by hairs from small tip to medium middle and from medium tip to large middle. Cochlea hair-cell receptors microscopic fibers and microscopic cross-fibers cause resonance between frequencies.
Oval-window movement makes pressure waves, down vestibular canal, which cause middle-canal vertical movement, which slides tectorial-membrane gel horizontally over upright cilia. If pushed one way, hair-cell-membrane potential increases from resting potential. If pushed other way, potential decreases. Inner hair cells send to 10 to 30 auditory neurons.
Outer hair cells can receive brain signals to extend cilia, to stiffen cochlear partition and dampen sound. This reduces signal-to-noise ratio, lowers required input intensity to sharpen tuning, or sends secondary signals to inner hair cells.
Stapes connects to membrane across opening {oval window, hearing}| at cochlea beginning. Oval window is 18 times smaller than tympanic membrane, to concentrate sound pressure.
At base, tympanic canal has soft tissue {round window} that absorbs high pressure.
Cochlea outside has a canal {tympanic canal} {scala tympani}. Tympanic membrane is over tympanic-canal end. Round window is over tympanic-canal base.
Cochlea outside has a canal {vestibular canal} {scala vestibuli}.
Tympanic and vestibular canals join at cochlea point {helicotrema}.
Cochlea middle has a canal {middle canal} {scala media}.
Cochlea inside has a canal {cochlear canal}.
Membrane {Reissner's membrane} separates middle canal and vestibular canal.
In cochlear canal, a coil {basilar membrane} also separates middle canal and tympanic canal. Close to oval window {base, basilar membrane}, basilar membrane is stiff and narrow. At other end {apex, basilar membrane}, basilar membrane is wider and less stiff.
Basilar-membrane structures {organ of Corti} have 30,000 hair-cell receptors, with stereocilia and fibers. Organ-of-Corti base detects high frequencies, and organ-of-Corti apex detects low frequencies (place code).
Gel membrane {tectorial membrane} attaches to end of, and floats in, middle canal and touches outer hair cells.
Basilar membrane, tectorial membrane, and organ of Corti together {cochlear partition} detect sounds. Cochlear partition is in middle canal.
1-Consciousness-Sense-Hearing-Anatomy
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Date Modified: 2022.0225