Ossicles

Source: Wikipedia, the free encyclopedia.
This article is about the bones in the human ear. For elements embedded in the body wall of echinoderms, see Ossicle (echinoderm).
This article is one of a series documenting the anatomy of the
Human ear
Outer ear
Middle ear
Inner ear

The ossicles (also called auditory ossicles) are three

labyrinth (cochlea). The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss. The term "ossicle" literally means "tiny bone". Though the term may refer to any small bone throughout the body, it typically refers to the malleus, incus, and stapes (hammer, anvil, and stirrup) of the middle ear
.

Structure

See also: Malleus, Incus, and Stapes
Anatomy of the three ossicles

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".[1]

Development

Studies have shown that ear bones in mammal embryos are attached to the

articular, and angular structures in the amphibian, bird or reptile jaw.[3]

Evolution

Main article: Evolution of mammalian auditory ossicles

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 (oval window), the opening to the vestibule of the inner ear.

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.[4] This is observed from the abrupt cessation of sound that occurs when the head is submerged underwater. This is because the relative incompressibility of a liquid presents resistance to the force of the sound waves traveling through the air. 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 allows more efficient coupling than if the sound waves were transmitted directly from the outer ear to the oval window. 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. The increased pressure will compress the fluid found in the cochlea and transmit the stimulus. 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.

However, the extent of the movements of the ossicles is controlled (and constricted) by two muscles attached to them (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).

Clinical relevance

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 using a passive middle ear implant.[further explanation needed]

History

There is some doubt as to the discoverers of the auditory ossicles and several anatomists from the early 16th century have the discovery attributed to them with the two earliest being

University of Naples as early as 1546.[14]

The term ossicle derives from ossiculum, a

genitive ossis).[15] The malleus gets its name from Latin malleus, meaning "hammer",[16] the incus gets its name from Latin incus meaning "anvil" from incudere meaning "to forge with a hammer",[17] and the stapes gets its name from Modern Latin "stirrup", probably an alteration of Late Latin stapia related to stare "to stand" and pedem, an accusative of pes "foot", so called because the bone is shaped like a stirrup – this was an invented Modern Latin word for "stirrup", for which there was no classical Latin word, as the ancients did not use stirrups.[18]

See also

This article uses anatomical terminology.

References

  1. PMID 36798057
    .
  2. ^ "Your Bones". kidshealth.org.
  3. OCLC 108462086
    .
  4. ^ Hill, R.W., Wyse, G.A. & Anderson, M. (2008). Animal Physiology, 2nd ed..
  5. PMID 14480894
    .
  6. ^ Alidosi, GNP. I dottori Bolognesi di teologia, filosofia, medicina e d'arti liberali dall'anno 1000 per tutto marzo del 1623, Tebaldini, N., Bologna, 1623. http://gallica.bnf.fr/ark:/12148/bpt6k51029z/f35.image#
  7. ^ Lind, L. R. Studies in pre-Vesalian anatomy. Biography, translations, documents, American Philosophical Society, Philadelphia, 1975. p.40
  8. ^ Jacopo Berengario da Carpi,Commentaria super anatomia Mundini, Bologna, 1521. https://archive.org/details/ita-bnc-mag-00001056-001
  9. ^ a b O'Malley, C.D. Andreas Vesalius of Brussels, 1514–1564. Berkeley: University of California Press, 1964. p. 120
  10. ^ Niccolo Massa, Liber introductorius anatomiae, Venice, 1536. p.166. https://www.digitale-sammlungen.de/en/view/bsb10151904?page=1
  11. ^ Andreas Vesalius, De humani corporis fabrica. Johannes Oporinus, Basle, 1543.
  12. ^ O'Malley, C.D. Andreas Vesalius of Brussels, 1514–1564. Berkeley: University of California Press, 1964. p. 121
  13. ^ Pedro Jimeno, Dialogus de re medica, Johannes Mey, Valencia, 1549. https://archive.org/details/dialogusderemed00jimegoog
  14. S2CID 30466939
    .
  15. ^ "Online Etymology Dictionary". etymonline.com.
  16. ^ "Online Etymology Dictionary". etymonline.com.
  17. ^ "Online Etymology Dictionary". etymonline.com.
  18. ^ "Online Etymology Dictionary". etymonline.com.

External links

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