Editing Ear (section)

===Hearing===
{{Main|Hearing}}
[[Sound wave]]s travel through the outer ear, are modulated by the middle ear, and are transmitted to the [[vestibulocochlear nerve]] in the inner ear. This nerve transmits information to the [[temporal lobe]] of the brain, where it is registered as sound.

Sound that travels through the outer ear impacts on the eardrum, and causes it to vibrate. The three ossicles bones transmit this sound to a second window (the [[oval window]]), which protects the fluid-filled inner ear. In detail, the pinna of the outer ear helps to focus a sound, which impacts on the eardrum. The malleus rests on the membrane, and receives the vibration. This vibration is transmitted along the incus and stapes to the oval window. Two small muscles, the [[tensor tympani]] and [[stapedius]], also help modulate noise. The two muscles [[Acoustic reflex|reflexively contract]] to dampen excessive vibrations. Vibration of the oval window causes vibration of the endolymph within the [[vestibule of the ear|vestibule]] and the cochlea.<ref name=HALL2005 >{{cite book|last=Hall|first=Arthur C. Guyton, John E.|title=Textbook of medical physiology|year=2005|publisher=W.B. Saunders|location=Philadelphia|isbn=978-0-7216-0240-0|pages=651–657|edition=11th}}</ref>

The inner ear houses the apparatus necessary to [[transduction (physiology)|change the vibrations]] transmitted from the outside world via the middle ear into signals passed along the vestibulocochlear nerve to the brain. The hollow channels of the inner ear are filled with liquid, and contain a sensory [[epithelium]] that is studded with [[hair cells]]. The microscopic "hairs" of these cells are structural protein filaments that project out into the fluid. The hair cells are [[mechanoreceptor]]s that release a chemical [[neurotransmitter]] when stimulated. Sound waves moving through fluid flows against the [[Receptor (biochemistry)|receptor]] cells of the organ of Corti. The fluid pushes the filaments of individual cells; movement of the filaments causes receptor cells to become open to receive the [[potassium]]-rich endolymph. This causes the cell to depolarise, and creates an [[action potential]] that is transmitted along the [[spiral ganglion]], which sends information through the auditory portion of the vestibulocochlear nerve to the [[temporal lobe]] of the brain.<ref name=HALL2005 />

The human ear can generally hear sounds with frequencies between 20 [[Hertz|Hz]] and 20 [[kHz]] ([[Sound#Perception|the audio range]]). Sounds outside this range are considered [[infrasound]] (below 20&nbsp;Hz)<ref>Greinwald, John H. Jr MD; Hartnick, Christopher J. MD The Evaluation of Children With Sensorineural Hearing Loss. [[JAMA Otolaryngology–Head & Neck Surgery|Archives of Otolaryngology–Head & Neck Surgery]]. 128(1):84–87, January 2002</ref> or [[ultrasound]] (above 20&nbsp;kHz)<ref>{{Cite web|url=http://www.collinsdictionary.com/dictionary/english/ultrasound|title=Definition of "ultrasound" {{!}} Collins English Dictionary|website=www.collinsdictionary.com|access-date=2016-03-20}}</ref> Although hearing requires an intact and functioning auditory portion of the [[central nervous system]] as well as a working ear, human deafness (extreme insensitivity to sound) most commonly occurs because of abnormalities of the inner ear, rather than in the nerves or tracts of the central auditory system.