The ''stapes'' or stirrup is a

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, ...

in the middle ear 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 th ...

. 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

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 being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body. It comprises a hea ...

, 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 auditor ...

in the middle ear and the smallest in the human body. It measures roughly , greater along the head-base span. It rests on the

, to which it is connected by an annular ligament and articulates with the '' incus'', or anvil through the incudostapedial joint. They are connected by anterior and posterior limbs ( la, crura).

Development

The ''stapes'' develops from the second pharyngeal 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; 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 rhynchocephalia ...

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 supporting either the spiracle or the jaw, depending on the species. The equivalent term in

amphibian Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...

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 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 strirrup bone of the middle ear. Structure The stapedius emerges fr ...

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 taste ...

Clinical relevance

Otosclerosis is a congenital or spontaneous-onset disease characterized by abnormal bone remodeling 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. 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, 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, 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

* {{Good article Auditory system Skeletal system Skull Ossicles