![]() 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. Ordinarily, when sound waves in air strike liquid, most of the energy is reflected off the surface of the liquid. The chorda tympani is the branch of the facial nerve that carries taste from the ipsilateral half (same side) of the tongue.įunction Sound transfer Damage to the horizontal branch during ear surgery can lead to paralysis of the face (same side of the face as the ear). These are the horizontal portion of the facial nerve and the chorda tympani. Of surgical importance are two branches of the facial nerve that also pass through the middle ear space. These muscles contract in response to loud sounds, thereby reducing the transmission of sound to the inner ear. 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 and is under the control of the medial pterygoid nerve which is a branch of the mandibular nerve of the trigeminal nerve. The movement of the ossicles may be stiffened by two muscles. Main articles: Stapedius muscle and Tensor tympani 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 middle ear efficiency peaks at a frequency of around 1 kHz. ![]() The auditory ossicles can also reduce sound pressure (the inner ear is very sensitive to overstimulation), by uncoupling each other through particular muscles. 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. In addition, the eardrum itself moves in a very chaotic fashion at frequencies >3 kHz. The eardrum is actually attached to the malleus handle over about a 0.5 cm distance. 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) and the level of the middle of the stapes. Between 0.1 and 1 kHz it is approximately 2, it then rises to around 5 at 2 kHz and then falls off steadily above this frequency. There is a steadily increasing body of evidence that shows that the lever arm ratio is actually variable, depending on frequency. ![]() Vibrations of the stapes footplate introduce pressure waves in the inner ear. The eardrum is merged to the malleus, which connects to the incus, which in turn connects to the stapes. ![]() 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 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. While the stapes is present in all tetrapods, the malleus and incus evolved from lower and upper jaw bones present in reptiles. The ossicles directly couple sound energy from the eardrum to the oval window of the cochlea. The ossicles were given their Latin names for their distinctive shapes they are also referred to as the hammer, anvil, and stirrup, respectively. The middle ear contains three tiny bones known as the ossicles: malleus, incus, and stapes. 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. The auditory tube (also known as the Eustachian tube or the pharyngotympanic tube) joins the tympanic cavity with the nasal cavity ( nasopharynx), allowing pressure to equalize between the middle ear and throat. The hollow space of the middle ear is also known as the tympanic cavity and is surrounded by the tympanic part of the temporal bone. The mammalian middle ear contains three ossicles (malleus, incus, and stapes), which transfer the vibrations of the eardrum into waves in the fluid and membranes of the inner ear. The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear).
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