|
| |
auris media
|
| |
230
|
| |
1037
|
| |
|
| |
|
| |
|
| |
|
| |
Middle ear map
|
| |
None
|
| |
Bones and muscles in the tympanic cavity in the middle ear
|
| |
|
| |
|
| |
|
| |
|
| |
Glossopharyngeal Nerve
|
| |
|
| |
Middle+ear
|
| |
A09246397
|
| |
a_73
|
| |
12169777
|
The is the portion of the ear internal to the
Eardrum , and external to the
Oval Window of the
Cochlea . The mammalian middle ear contains three
Ossicles , which couple vibration of the eardrum into waves in the fluid and membranes of the
Inner Ear . The hollow space of the middle ear has also been called the
Tympanic Cavity , or ''cavum tympani''. The
Eustachian Tube joins the tympanic cavity with the nasal cavity (
Nasopharynx ), allowing pressure to equalize between the inner ear and throat.
The primary function of the middle ear is to efficiently transfer acoustic energy from compression waves in air to fluid–membrane waves within the
Cochlea .
Ordinarily, when sound waves in air strike liquid, most of the energy is reflected off the surface of the liquid. The middle ear allows the impedance matching of sound traveling in air to acoustic waves traveling in a system of fluids and membranes in the inner ear. This system should not be confused, however, with the propagation of sound as compression waves in a liquid.
The middle ear couples sound from air to the fluid via the oval window, using the principle of "mechanical advantage" in the form of the "hydraulic principle" and the "lever principle".
1 The vibratory portion of the tympanic membrane is many times the surface area of the footplate of the stapes; furthermore, the shape of the articulated ossicular chain is like a lever, the long arm being the long process of the malleus, and the body of the incus being the fulcrum and the short arm being the lenticular process of the incus. The collected pressure of sound vibration that strikes the tympanic membrane is therefore concentrated down to this much smaller area of the footplate, increasing the force but reducing the velocity and displacement, and thereby coupling the acoustic energy.
The middle ear is able to dampen sound conduction substantially when faced with very loud sound, by noise-induced reflex contraction of the middle-ear muscles.
The middle ear contains three tiny bones known as the '', ''
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 ear drum to the
Oval Window of the cochlea.
The ossicles are classically supposed to mechanically convert the vibrations of the (also known as the
Umbo ) and the level of the middle of the
Stapes . The
Eardrum is actually attached to the
Malleus handle over about a 1cm distance. In addition the
Eardrum itself moves in a very chaotic fashion at frequencies >3 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 kHz. The combined transfer function of the outer ear and middle ear gives humans a peak sensitivity to frequencies between 1 kHz and 3 kHz.
The movement of the ossicles may be stiffened by two muscles, the stapedius and tensor tympani, which are under the control of the
Facial Nerve and
Trigeminal Nerve , respectively. These muscles contract in response to loud sounds, thereby reducing the transmission of sound to the inner ear. This is called the
Acoustic Reflex .
Of surgical importance are two branches of the
Facial Nerve which also pass through the middle ear space. These are the horizontal and ''chorda tympani'' branches of the facial nerve. Damage to the horizontal branch during surgery can lead to partial, unilateral facial paralysis.
Mammals are unique in having three ear bones. The incus and stapes have evolved from bones of the jaw, and allow finer detection of sound.
Some mammals, such as the
Cat , have an enlarged middle ear encased in a thin, bulbous bone; this structure is known as a bulla.
The middle ear is hollow. If the animal moves to a high-altitude environment, or dives into the water, there will be a pressure difference between the middle ear and the outside environment. This pressure will pose a risk of bursting or otherwise damaging the tympanum if it is not relieved. This is one of the functions of the
Eustachian Tube s which connect the middle ear to the
Nasopharynx . The Eustachian tubes are normally pinched off at the nose end, to prevent being clogged with
Mucus , but they may be opened by lowering and protruding the jaw; this is why
Yawn ing helps relieve the pressure felt in the ears when on board an aircraft.
Otitis Media is an inflammation of the middle ear.
Image:Gray919.png
