Dictionary Definition
User Contributed Dictionary
English
Pronunciation
- IPA:/ɒsɪkəl/
Noun
- A small bone (or bony
structure), especially one of the three of the middle ear.
- The incus is one of the three auditory ossicles.
- Quotations
-
- 1836: The eyeballs were surrounded by a ring of bones, the sclerotic ossicle, which probably protected their eyes when diving abruptly for prey. — William Buckland, Geology and Mineralogy, Considered with Reference to Natural Theology, vol. 1, William Pickering, 1836, p. 174
- The incus is one of the three auditory ossicles.
- Bone-like joint or
plate, especially:
-
- one of numerous small calcareous structures forming the skeleton of certain echinoderms, as the starfishes;
- one of the hard articuli or joints of the stem or branches of a crinoid or encrinite;
- one of the several small hard chitinous parts or processes of the gastric skeleton of crustaceans, as in the stomach of a lobster or crawfish.
- The skeleton of echinoderms is made of ossicles, linked to each other via muscles and connective tissue.
-
Synonyms
Derived terms
- ambulacral ossicle
- Andernach's ossicles
- cardiac ossicle
- carpal ossicle
- epactal ossicles
- episternal ossicles
- intercalcar ossicles
- Kerckring's (Kerkring's) ossicle
- marginal ossicles
- ossicle of Bertin
- ossicular
- ossiculate
- ossiculectomy
- ossiculotomy
- Riolan's ossicles
- sphenoturbinal ossicle
- tarsal ossicle
- vertebral ossicle
- Weberian ossicles
- wormian ossicles
Related terms
See os.Translations
bone-like plate
Extensive Definition
The ossicles (also called auditory ossicles) are
the three smallest bones in
the human body. They are contained within the middle ear
space and serve to transmit sounds from the air to the
fluid-filled labyrinth
(cochlea). The absence
of the auditory ossicles would constitute a moderate-to-severe
hearing
loss.
Anatomy
The ossicles are, in order from the eardrum to the inner ear, the hammer, anvil, and stirrup, so named because of the shape of the bones. They are also commonly referred to by the equivalent Latin terms: malleus, incus, and stapes respectively.- The malleus articulates with the incus and is attached to the tympanic membrane (eardrum), from which vibrational energy is passed.
- The incus is connected to both the other bones.
- The stapes articulates with the incus 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.
Function
As sound waves vibrate the tympanic membrane (eardrum), it in turn moves the nearest ossicle, the malleus, to which it is attached. The malleus then transmits the vibrations, via the incus, to the stapes, and so ultimately to the membrane of the fenestra ovalis, the opening to the vestibule of the inner ear.The ossicles give the eardrum mechanical
advantage via lever action and a reduction in the area of force
distribution; the resulting vibrations would be much smaller if the
sound waves were transmitted directly from the outer ear to the
oval window. However, the extent of the movements of the ossicles
is controlled (and constricted) by certain muscles attached to them
(the tensor
tympani and the stapedius). It is believed
that these muscles can contract to dampen the vibration of the
ossicles, in order to protect the inner ear from excessively loud
noise (theory 1) and that they give better frequency resolution at
higher frequencies by reducing the transmission of low frequencies
(theory 2) (see acoustic
reflex). These muscles are more highly developed in bats and serve to block outgoing
cries of the bats during echolocation (SONAR).
Occasionally the joints between the ossicles
become rigid. One condition, otosclerosis, results in
the fusing of the stapes to the oval window. This reduces hearing
and may be treated surgically.
Development
Studies have shown that ear bones in mammal embryos are attached to the dentary, which is part of the jaw. These are ossified portions of cartilage -- called Meckel's cartilage -- that are attached to the jaw. As the embryo develops, the cartilage hardens to form bone. Later in development, the bone structure breaks loose from the jaw and migrates to the inner ear area. The structure is known as the middle ear, and is made up of the incus, stapes, malleus, and tympanic membrane. These correspond to the quadrate, preartiluar, articular, and angular structures in the reptile jaw. For this reason, researchers believe the similarity results mammals and reptiles having a common ancestry.ossicle in German: Gehörknöchelchen
ossicle in Estonian: Kuulmeluud
ossicle in Spanish: Cadena de huesecillos
ossicle in French: Osselet (oreille)
ossicle in Korean: 이소골
ossicle in Lithuanian: Klausomieji
kauliukai
ossicle in Dutch: Gehoorbeentje
ossicle in Japanese: 耳小骨
ossicle in Polish: Kosteczki słuchowe
ossicle in Slovak: Sluchové kostičky
ossicle in Finnish: Kuuloluut
ossicle in Thai: กระดูกหู
ossicle in Chinese: 听小骨