ossicles
   HOME

TheInfoList



OR:

The ossicles (also called auditory ossicles) are three irregular bones in the middle ear of
human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
s and other
mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s, and are among the smallest
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
s in the human body. Although the term "ossicle" literally means "tiny bone" (from
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
''ossiculum'') and may refer to any small bone throughout the body, it typically refers specifically to the malleus,
incus The ''incus'' (: incudes) or anvil in the ear is one of three small bones (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 i ...
and stapes ("hammer, anvil, and stirrup") of the middle ear. The auditory ossicles serve as a kinematic chain to transmit and amplify ( intensify)
sound In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the br ...
vibrations collected from the air by the ear drum to the fluid-filled labyrinth ( cochlea). The absence or pathology of the auditory ossicles would constitute a moderate-to-severe conductive hearing loss.


Structure

The ossicles are, in order from the eardrum to the inner ear (from superficial to deep): the malleus,
incus The ''incus'' (: incudes) or anvil in the ear is one of three small bones (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 i ...
, and stapes, terms that in
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
are translated as "the
hammer A hammer is a tool, most often a hand tool, consisting of a weighted "head" fixed to a long handle that is swung to deliver an impact to a small area of an object. This can be, for example, to drive nail (fastener), nails into wood, to sh ...
,
anvil An anvil is a metalworking tool consisting of a large block of metal (usually Forging, forged or Steel casting, cast steel), with a flattened top surface, upon which another object is struck (or "worked"). Anvils are massive because the hi ...
, and stirrup". * The malleus () 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
incus The ''incus'' (: incudes) or anvil in the ear is one of three small bones (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 i ...
() is connected to both the other bones. * The stapes () 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 inner ear (internal ear, auris interna) 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 ...
. It is the smallest bone in the body.


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 Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...
—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 The ''incus'' (: incudes) or anvil in the ear is one of three small bones (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 i ...
, malleus, and tympanic membrane. These correspond to the columella, quadrate, articular, and angular structures in the amphibian, bird or reptile jaw.


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. 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 Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...
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 In electrical engineering, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or ...
. 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 The acoustic reflex (also known as the stapedius reflex, stapedial reflex, auditory reflex, middle-ear-muscle reflex (MEM reflex, MEMR), attenuation reflex, cochleostapedial reflex or intra-aural reflex) is an involuntary muscle contraction that ...
). 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.


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. Several sources, including Eustachi and Casseri, attribute the discovery of the malleus and incus to the anatomist and philosopher Achillini. The first written description of the malleus and incus was by Berengario da Carpi in his ''Commentaria super anatomia Mundini'' (1521), although he only briefly described two bones and noted their theoretical association with the transmission of sound.O'Malley, C.D. ''Andreas Vesalius of Brussels, 1514–1564.'' Berkeley: University of California Press, 1964. p. 120 Niccolo Massa's ''Liber introductorius anatomiae'' described the same bones in slightly more detail and likened them both to little hammers. A much more detailed description of the first two ossicles followed in
Andreas Vesalius Andries van Wezel (31 December 1514 – 15 October 1564), latinized as Andreas Vesalius (), was an anatomist and physician who wrote '' De Humani Corporis Fabrica Libri Septem'' (''On the fabric of the human body'' ''in seven books''), which is ...
' '' De humani corporis fabrica'' 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. The first published description of the stapes came in Pedro Jimeno's ''Dialogus de re medica'' (1549) although it had been previously described in public lectures by Giovanni Filippo Ingrassia at the
University of Naples The University of Naples Federico II (; , ) is a public university, public research university in Naples, Campania, Italy. Established in 1224 and named after its founder, Frederick II, Holy Roman Emperor, Frederick II, it is the oldest public, s ...
as early as 1546. The term ''ossicle'' derives from , a
diminutive A diminutive is a word obtained by modifying a root word to convey a slighter degree of its root meaning, either to convey the smallness of the object or quality named, or to convey a sense of intimacy or endearment, and sometimes to belittle s ...
of "bone" (; genitive ). The malleus gets its name from Latin ''malleus'', meaning "hammer", the incus gets its name from Latin ''incus'' meaning "anvil" from incudere meaning "to forge with a hammer", 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.


See also

*
Evolution of mammalian auditory ossicles The evolution of mammalian auditory ossicles was an evolutionary process that resulted in the formation of the mammalian middle ear, where the three middle ear bones or ossicles, namely the incus, malleus and stapes (a.k.a. "the anvil, hammer, and ...
* * *


References


External links


The middle ear and the ossicles
{{Authority control Auditory system Bones of the head and neck Otorhinolaryngology Otology Human head and neck Ear Middle ear