The ''stapes'' or stirrup is a
bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
in the
middle ear
The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear).
The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the ...
of humans and other animals which is involved in the conduction of sound vibrations to 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 ...
. This bone is connected to the
oval window
The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea of the inner ear.
Vibrations that contact the tympanic membrane travel through the three ossicles and into the in ...
by its
annular ligament, which allows the footplate to transmit sound energy through the
oval window
The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea of the inner ear.
Vibrations that contact the tympanic membrane travel through the three ossicles and into the in ...
into the inner ear. The ''stapes'' is the smallest and lightest bone in the
human body
The human body is the structure of a Human, human being. It is composed of many different types of Cell (biology), cells that together create Tissue (biology), tissues and subsequently organ systems. They ensure homeostasis and the life, viabi ...
, and is so-called because of its resemblance to a
stirrup
A stirrup is a light frame or ring that holds the foot of a rider, attached to the saddle by a strap, often called a ''stirrup leather''. Stirrups are usually paired and are used to aid in mounting and as a support while using a riding animal ( ...
( la, Stapes).
Structure
The ''stapes'' is the third bone of the three
ossicles
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 ...
in the
middle ear
The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear).
The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the ...
and the smallest in the human body. It measures roughly , greater along the head-base span. It rests on the
oval window
The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea of the inner ear.
Vibrations that contact the tympanic membrane travel through the three ossicles and into the in ...
, to which it is connected by an
annular ligament and articulates with the ''
incus
The ''incus'' (plural incudes) 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 transmit ...
'', or anvil through the
incudostapedial joint
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 lon ...
.
[ They are connected by anterior and posterior limbs ( la, crura).]
Development
The ''stapes'' develops from the second pharyngeal arch
The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arch ...
during the sixth to eighth week of embryological life. The central cavity of the ''stapes'', the ''obturator foramen'', is due to the presence embryologically of the stapedial artery, which usually regresses in humans during normal development.
Animals
The ''stapes'' is one of three ossicles in mammals. In non-mammalian four-legged animals, the bone homologous to the ''stapes'' is usually called the columella
Lucius Junius Moderatus Columella (; Arabic: , 4 – ) was a prominent writer on agriculture in the Roman Empire.
His ' in twelve volumes has been completely preserved and forms an important source on Roman agriculture, together with the wo ...
; however, in reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s, either term may be used. In fish, the homologous bone is called the hyomandibula
The hyomandibula, commonly referred to as hyomandibular one( la, os hyomandibulare, from el, hyoeides, "upsilon-shaped" (υ), and Latin: mandibula, "jawbone") is a set of bones that is found in the hyoid region in most fishes. It usually plays ...
r, and is part of the gill arch
Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arc ...
supporting either the spiracle Spiracle or spiraculum may refer to:
* Spiracle (arthropods), opening in the exoskeletons of some arthropods
* Spiracle (vertebrates), openings on the surface of some vertebrates
* Spiraculum, a genus of land snails in family Cyclophoridae
Cycl ...
or the jaw, depending on the species. The equivalent term in amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s is the '.
Variation
The ''stapes'' appears to be relatively constant in size in different ethnic groups. In 0.01–0.02% of people, the stapedial artery does not regress, and persists in the central foramen. In this case, a pulsatile sound may be heard in the affected ear, or there may be no symptoms at all. Rarely, the ''stapes'' may be completely absent.
Function
Situated between the incus and the inner ear, the ''stapes'' transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear. The ''stapes'' is also stabilized by the stapedius muscle, which is innervated by the facial nerve
The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of tas ...
.
Clinical relevance
Otosclerosis
Otosclerosis is a condition of the middle ear where portions of the dense enchondral layer of the bony labyrinth remodel into one or more lesions of irregularly-laid spongy bone. As the lesions reach the stapes the bone is resorbed, then har ...
is a congenital or spontaneous-onset disease characterized by abnormal bone remodeling
Bone remodeling (or bone metabolism) is a lifelong process where mature bone tissue is removed from the skeleton (a process called ''bone resorption'') and new bone tissue is formed (a process called ''ossification'' or ''new bone formation''). T ...
in the inner ear. Often this causes the ''stapes'' to adhere to the oval window, which impedes its ability to conduct sound, and is a cause of conductive hearing loss
Conductive hearing loss (CHL) occurs when there is a problem transferring sound waves anywhere along the pathway through the outer ear, tympanic membrane (eardrum), or middle ear ( ossicles). If a conductive hearing loss occurs in conjunction wi ...
. Clinical otosclerosis is found in about 1% of people, although it is more common in forms that do not cause noticeable hearing loss. Otosclerosis is more likely in young age groups, and females. Two common treatments are stapedectomy
A stapedectomy is a surgical procedure of the middle ear performed in order to improve hearing.
If the stapes footplate is fixed in position, rather than being normally mobile, the result is a conductive hearing loss. There are two major causes ...
, the surgical removal of the ''stapes'' and replacement with an artificial prosthesis, and stapedotomy, the creation of a small hole in the base of the ''stapes'' followed by the insertion of an artificial prosthesis into that hole. Surgery may be complicated by a persistent stapedial artery, fibrosis
Fibrosis, also known as fibrotic scarring, is a pathological wound healing in which connective tissue replaces normal parenchymal tissue to the extent that it goes unchecked, leading to considerable tissue remodelling and the formation of perma ...
-related damage to the base of the bone, or obliterative otosclerosis, resulting in obliteration of the base.
History
The ''stapes'' is commonly described as having been discovered by the professor Giovanni Filippo Ingrassia
Giovanni Filippo Ingrassia or Ioannis Philippi Ingrassiae (1510–1580) was an Italian physician, student of Vesalius, professor at the University of Naples, ''Protomedicus'' of Sicily and a major figure in the history of medicine and human anatomy ...
in 1546 at the University of Naples
The University of Naples Federico II ( it, Università degli Studi di Napoli Federico II) is a public university in Naples, Italy. Founded in 1224, it is the oldest public non-sectarian university in the world, and is now organized into 26 depar ...
, although this remains the nature of some controversy, as Ingrassia's description was published posthumously in his 1603 anatomical commentary '. Spanish anatomist Pedro Jimeno is first to have been credited with a published description, in (1549). The bone is so-named because of its resemblance to a stirrup ( la, stapes), an example of a late Latin
Late Latin ( la, Latinitas serior) is the scholarly name for the form of Literary Latin of late antiquity.Roberts (1996), p. 537. English dictionary definitions of Late Latin date this period from the , and continuing into the 7th century in t ...
word, probably created in mediaeval
In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...
times from "to stand" ( la, stapia), as stirrups did not exist in the early Latin-speaking world.
References
External links
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{{Good article
Auditory system
Skeletal system
Skull
Ossicles