Ossicles

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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 bones in either middle ear that are among the smallest bones in the human body. They 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. 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.

Contents

Structure

Anatomy of the three ossicles Slide1ghe.JPG
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 dentary, which is part of the lower 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 stapes, incus, malleus, and tympanic membrane. These correspond to the columella, quadrate, articular, and angular structures in the amphibian, bird or reptile jaw. [3]

Evolution

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 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).

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 Alessandro Achillini and Jacopo Berengario da Carpi. [5] Several sources, including Eustachi and Casseri, [6] attribute the discovery of the malleus and incus to the anatomist and philosopher Achillini. [7] The first written description of the malleus and incus was by Berengario da Carpi in his Commentaria super anatomia Mundini (1521), [8] although he only briefly described two bones and noted their theoretical association with the transmission of sound. [9] Niccolo Massa's Liber introductorius anatomiae [10] described the same bones in slightly more detail and likened them both to little hammers. [9] A much more detailed description of the first two ossicles followed in Andreas Vesalius' De humani corporis fabrica [11] in which he devoted a chapter to them. Vesalius was the first to compare the second element of the ossicles to an anvil although he offered the molar as an alternative comparison for its shape. [12] The first published description of the stapes came in Pedro Jimeno's Dialogus de re medica (1549) [13] although it had been previously described in public lectures by Giovanni Filippo Ingrassia at the University of Naples as early as 1546. [14]

The term ossicle derives from ossiculum, a diminutive of "bone" (Latin : os; 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

Related Research Articles

<span class="mw-page-title-main">Inner ear</span> Innermost part of the vertebrate ear

The inner ear is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:

<span class="mw-page-title-main">Middle ear</span> Portion of the ear internal to the eardrum, and external to the oval window 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.

<span class="mw-page-title-main">Incus</span> Bone in the middle ear

The incus or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The incus receives vibrations from the malleus, to which it is connected laterally, and transmits these to the stapes medially. The incus is so-called because of its resemblance to an anvil.

<i>Stapes</i> Bone in the middle ear

The stapes or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its annular ligament, which allows the footplate to transmit sound energy through the oval window into the inner ear. The stapes is the smallest and lightest bone in the human body, and is so-called because of its resemblance to a stirrup.

<span class="mw-page-title-main">Oval window</span> Membrane-covered opening in the ear

The oval window is a connective tissue membrane-covered opening from the middle ear to the cochlea of the inner ear.

<span class="mw-page-title-main">Eardrum</span> Membrane separating the external ear from the middle ear

In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear from the middle ear. Its function is to transmit sound from the air to the ossicles inside the middle ear, and then to the oval window in the fluid-filled cochlea. Hence, it ultimately converts and amplifies vibration in the air to vibration in cochlear fluid. The malleus bone bridges the gap between the eardrum and the other ossicles.

<span class="mw-page-title-main">Cochlea</span> Snail-shaped part of inner ear involved in hearing

The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the organ of Corti, the sensory organ of hearing, which is distributed along the partition separating the fluid chambers in the coiled tapered tube of the cochlea.

<span class="mw-page-title-main">Auditory system</span> Sensory system used for hearing

The auditory system is the sensory system for the sense of hearing. It includes both the sensory organs and the auditory parts of the sensory system.

<span class="mw-page-title-main">Ear</span> Organ of hearing and balance

An ear is the organ that enables hearing and body balance using the vestibular system. In mammals the ear is usually described as having three parts: the outer ear, the middle ear and the inner ear. The outer ear consists of the pinna and the ear canal. Since the outer ear is the only visible portion of the ear in most animals, the word "ear" often refers to the external part alone. The middle ear includes the tympanic cavity and the three ossicles. The inner ear sits in the bony labyrinth, and contains structures which are key to several senses: the semicircular canals, which enable balance and eye tracking when moving; the utricle and saccule, which enable balance when stationary; and the cochlea, which enables hearing. The ear is a self cleaning organ through its relationship with earwax and the ear canals. The ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localization.

<span class="mw-page-title-main">Tympanoplasty</span> Surgical operation on the ear

Tympanoplasty is the surgical operation performed to reconstruct hearing mechanism of middle ear.

<span class="mw-page-title-main">Stapedius muscle</span> Muscle in the human ear

The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes or stirrup bone of the middle ear.

<span class="mw-page-title-main">Tensor tympani muscle</span> Muscle of the middle ear

The tensor tympani is a muscle within the middle ear, located in the bony canal above the bony part of the auditory tube, and connects to the malleus bone. Its role is to dampen loud sounds, such as those produced from chewing, shouting, or thunder. Because its reaction time is not fast enough, the muscle cannot protect against hearing damage caused by sudden loud sounds, like explosions or gunshots.

<span class="mw-page-title-main">Tympanic cavity</span> Small cavity surrounding the bones of the middle ear

The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound.

<span class="mw-page-title-main">Evolution of mammalian auditory ossicles</span> Middle ear bones evolved from jaw bones

The evolution of mammalian auditory ossicles was an evolutionary process that resulted in the formation of the bones of the mammalian middle ear. These bones, or ossicles, are a defining characteristic of all mammals. The event is well-documented and important as a demonstration of transitional forms and exaptation, the re-purposing of existing structures during evolution.

<span class="mw-page-title-main">Hearing</span> Sensory perception of sound by living organisms

Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory science.

<span class="mw-page-title-main">Columella (auditory system)</span> Bony structures in the skull that serve the purpose of transmitting sounds

In the auditory system, the columella contributes to hearing in amphibians, reptiles and birds. The columella form thin, bony structures in the interior of the skull and serve the purpose of transmitting sounds from the eardrum. It is an evolutionary homolog of the stapes, one of the auditory ossicles in mammals.

<span class="mw-page-title-main">Incudomalleolar joint</span> Synovial joint between malleus and incus

The incudomalleolar joint or articulatio incudomallearis is a small synovial joint between the malleus (hammer) and the incus (anvil). The joint's function is to transfer vibrations between the ossicles in the middle ear, which is perceived as sound. Contrary to other synovial joints the movement is very limited. All of the ossicles move more or less as a unit, at least at low frequencies.

<span class="mw-page-title-main">Incudostapedial joint</span> Small joint between the incus and the stapes

Incudostapedial joint is a small, synovial ball-and-socket joint between the incus (anvil) and the stapes (stirrup). The joint's function is to transfer vibrations between the two ossicles. The incudostapedial joint lies between the long leg of the incus and the head of the stapes. The long leg moves with the rest of the incus, and a small knob, the lenticular process, articulates with the head of the stapes.

In medicine, an ossicular replacement prosthesis is a device intended to be implanted for the functional reconstruction of segments of the ossicles and facilitates the conduction of sound waves from the tympanic membrane to the inner ear. There are two common types of ossicular replacement prostheses, the total ossicular replacement prosthesis (TORP) and partial ossicular replacement prosthesis (PORP). A TORP replaces the entire ossicular chain while a PORP replaces only the incus and malleus but not the stapes. Indications for use of an ossicular replacement prosthesis include:

<span class="mw-page-title-main">Malleus</span> Hammer-shaped small bone of the middle ear

The malleus, or hammer, is a hammer-shaped small bone or ossicle of the middle ear. It connects with the incus, and is attached to the inner surface of the eardrum. The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibrations from the eardrum to the incus (anvil).

References

  1. ↑ Hilal, Fathi; Liaw, Jeffrey; Cousins, Joseph P.; Rivera, Arnaldo L.; Nada, Ayman (2023-04-01). "Autoincudotomy as an uncommon etiology of conductive hearing loss: Case report and review of literature". Radiology Case Reports. 18 (4): 1461–1465. doi:10.1016/j.radcr.2022.10.097. ISSN   1930-0433. PMC   9925837 . PMID   36798057.
  2. ↑ "Your Bones". kidshealth.org.
  3. ↑ Meng, Jin (2003). "The Journey From Jaw to Ear". Biologist. 50 (4): 154–158. OCLC   108462086.
  4. ↑ Hill, R.W., Wyse, G.A. & Anderson, M. (2008). Animal Physiology, 2nd ed..
  5. ↑ O'Malley, C. D.; Clarke, E (1961). "The discovery of the auditory ossicles". Bulletin of the History of Medicine. 35: 419–41. 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. 1 2 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. ↑ Mudry, Albert (2013). "Disputes Surrounding the Discovery of the Stapes in the Mid 16th Century". Otology & Neurotology. 34 (3): 588–592. doi:10.1097/mao.0b013e31827d8abc. PMID   23370557. 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.
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