Thus, the lever action of the ossicles changes the vibrations so as to improve the transfer and reception of sound, and is a form of impedance matching.
The increased pressure will compress the fluid found in the cochlea and transmit the stimulus. This reduction in the area of force application allows a large enough increase in pressure to transfer most of the sound energy into the liquid. This allows more efficient coupling than if the sound waves were transmitted directly from the outer ear to the oval window.
The ossicles give the eardrum a mechanical advantage via lever action and a reduction in the area of force distribution the resulting vibrations are stronger but don't move as far. This is because the relative incompressibility of a liquid presents resistance to the force of the sound waves traveling through the air. This is observed from the abrupt cessation of sound that occurs when the head is submerged underwater. Sound traveling through the air is mostly reflected when it comes into contact with a liquid medium only about 1/30 of the sound energy moving through the air would be transferred into the liquid. The malleus then transmits the vibrations, via the incus, to the stapes, and so ultimately to the membrane of the fenestra ovalis (oval window), the opening to the vestibule of the inner ear. Main article: Evolution of mammalian auditory ossicles Function Īs sound waves vibrate the tympanic membrane (eardrum), it in turn moves the nearest ossicle, the malleus, to which it is attached. These correspond to the columella, quadrate, articular, and angular structures in the amphibian, bird or reptile jaw. The structure is known as the middle ear, and is made up of the stapes, incus, malleus, and tympanic membrane. Later in development, the bone structure breaks loose from the jaw and migrates to the inner ear area. As the embryo develops, the cartilage hardens to form bone. These are ossified portions of cartilage-called Meckel's cartilage-that are attached to the jaw. Studies have shown that ear bones in mammal embryos are attached to the dentary, which is part of the lower jaw. The stapes ( Latin: "stirrup") articulates with the incus through the incudostapedial joint and is attached to the membrane of the fenestra ovalis, the elliptical or oval window or opening between the middle ear and the vestibule of the inner ear.The incus ( Latin: "anvil") is connected to both the other bones.The malleus ( Latin: "hammer") articulates with the incus through the incudomalleolar joint and is attached to the tympanic membrane ( eardrum), from which vibrational sound pressure motion is passed.The ossicles are, in order from the eardrum to the inner ear (from superficial to deep): the malleus, incus, and stapes, terms that in Latin are translated as "the hammer, anvil, and stirrup".
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