Editing Middle ear (section)

==Structure==

===Ossicles===
The middle ear contains three tiny bones known as the [[ossicles]]: ''[[malleus]]'', ''[[incus]]'', and ''[[stapes]]''.  The ossicles were given their Latin names for their distinctive shapes; they are also referred to as the ''hammer'', ''anvil'', and ''stirrup'', respectively. The ossicles directly couple sound energy from the eardrum to the [[oval window]] of the cochlea.  While the stapes is present in all [[tetrapods]], the malleus and incus [[Evolution of mammalian auditory ossicles|evolved from lower and upper jaw bones present in reptiles]].

The ossicles are classically supposed to mechanically convert the vibrations of the [[eardrum]] into amplified pressure waves in the fluid of the [[cochlea]] (or [[inner ear]]), with a lever arm factor of 1.3. Since the effective vibratory area of the eardrum is about 14 fold larger than that of the oval window, the sound pressure is concentrated, leading to a pressure gain of at least 18.1. The eardrum is merged to the malleus, which connects to the incus, which in turn connects to the stapes. Vibrations of the stapes footplate introduce pressure waves in the [[inner ear]]. There is a steadily increasing body of evidence that shows that the lever arm ratio is actually variable, depending on frequency. Between 0.1 and 1&nbsp;kHz it is approximately 2, it then rises to around 5 at 2&nbsp;kHz and then falls off steadily above this frequency.<ref>{{cite journal |doi=10.1121/1.1451073 |title=Modeling of the human middle ear using the finite-element method |journal=The Journal of the Acoustical Society of America |volume=111 |issue=3 |pages=1306–1317 |year=2002 |last1=Koike |first1=Takuji |last2=Wada |first2=Hiroshi |last3=Kobayashi |first3=Toshimitsu |bibcode=2002ASAJ..111.1306K |pmid=11931308}}</ref> The measurement of this lever arm ratio is also somewhat complicated by the fact that the ratio is generally given in relation to the tip of the malleus (also known as the [[umbo of tympanic membrane|umbo]]) and the level of the middle of the stapes. The eardrum is actually attached to the malleus handle over about a 0.5&nbsp;cm distance. In addition, the eardrum itself moves in a very chaotic fashion at frequencies >3&nbsp;kHz. The linear attachment of the eardrum to the malleus actually smooths out this chaotic motion and allows the ear to respond linearly over a wider frequency range than a point attachment. The auditory ossicles can also reduce sound pressure (the inner ear is very sensitive to overstimulation), by uncoupling each other through particular muscles.

The middle ear efficiency peaks at a frequency of around 1&nbsp;kHz. The combined [[transfer function]] of the outer ear and middle ear gives humans a peak sensitivity to frequencies between 1&nbsp;kHz and 3&nbsp;kHz.

===Muscles===
{{Main|Stapedius muscle|Tensor tympani}}
The movement of the ossicles may be stiffened by two muscles. The [[stapedius muscle]], the smallest skeletal muscle in the body, connects to the stapes and is controlled by the [[facial nerve]]; the [[tensor tympani muscle]] is attached to the upper end of the medial surface of the handle of malleus<ref>{{Cite book |url=https://books.google.com/books?id=b7FVCgAAQBAJ&q=near+the+upper+end+of+its+medial+surface+there+is+a+slight+projection+to+which+tendon+of+tensor+tympani+is+attached |title=Gray's Anatomy E-Book: The Anatomical Basis of Clinical Practice |last=Standring |first=Susan |date=2015-08-07 |publisher=Elsevier Health Sciences |isbn=9780702068515 |language=en}}</ref> and is under the control of the [[medial pterygoid nerve]] which is a branch of the [[mandibular nerve]] of the [[trigeminal nerve]]. These muscles contract in response to loud sounds, thereby reducing the transmission of sound to the inner ear. This is called the [[acoustic reflex]].

===Nerves===
Of surgical importance are two branches of the [[facial nerve]] that also pass through the middle ear space.  These are the horizontal portion of the facial nerve and the [[chorda tympani]].  Damage to the horizontal branch during ear surgery can lead to  paralysis of the face (same side of the face as the ear).  The chorda tympani is the branch of the facial nerve that carries taste from the [[Anatomical terms of location#Medial and lateral|ipsilateral]] half (same side) of the tongue.