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.
Variation
Stapes
Stapes | Variation
It 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 rare cases, the stapes may be completely absent. It 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 It appears to be relatively constant in size in different ethnic groups, and rarely is it completely absent.
what are the 3 smallest bones in the human body
user
Strapes is one of them
assistant
what is the size of this above bone?
user
Roughly 3 x 2.5mm
assistant
which part of the body is this located?
user
Middle ear of humans
assistant
besides the human, is this bony structure present in other living species in the animal kingdom?
user
It is one of three ossicles in mammals, in non-mammalian four-legged animals its homologous form is called the columella
assistant
what are the functions this bony structure serves?
user
It transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear.
assistant
are there any variations of this bony structure?
user
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.
Stapes | Function
The stapes is the third bone of the three ossicles in the middle ear. The stapes is a stirrup-shaped bone, and the smallest in the human body. It rests on the oval window, to which it is connected by an annular ligament. The stapes is described as having a base, resting on the oval window, as well as a head that articulates with the incus. These are connected by anterior and posterior limbs (). The stapes articulates with the incus through the incudostapedial joint. The stapes is the smallest bone in the human body, and measures roughly 3 x 2.5mm, greater along the head-base span.
Stapes | Structure
The stapes or stirrup is a bone in the middle ear of humans and other mammals which is involved in the conduction of sound vibrations to the inner ear. This stirrup-shaped 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 ().
Stapes | Introduction
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 reptiles, either term may be used. In fish, the homologous bone is called the "hyomandibular", and is part of the gill arch supporting either the spiracle or the jaw, depending on the species. The equivalent term in amphibians is the "".
Stapes | Animals
The configuration of the stapes is intermediate between non-amniote tetrapods and amniotes. On the one hand, its connection to the otic notch is unusual, since true reptiles and other amniotes have lost an otic notch, forcing the tympanum and stapes to shift downwards towards the quadrate bone of the jaw joint. On the other hand, the thin, sensitive structure of "Seymouria"'s stapes is a specialization over most non-amniote tetrapods, which have a thick stapes useless for hearing yet useful for reinforcing the skull. The inner ear of "Seymouria baylorensis" retains a cochlear recess located behind (rather than below) the vestibule, and its anterior semicircular canal was likely encompassed by a cartilaginous (rather than bony) supraoccipital.
Seymouria | Skull
The morphology of the stapes suggests that the animal was capable of hearing high-frequency sound. "B. woodi" does not possess lateral line sulci or an ossified branchial system. The principal method of respiration was probably buccal (gulping air through mouth) rather than costal (expanding chest volume to take in air), indicated by the small straight ribs.
Balanerpeton | Introduction
The stapes bone transmits movement to the oval window. As the stapes footplate moves into the oval window, the round window membrane moves out, and this allows movement of the fluid within the cochlea, leading to movement of the cochlear inner hair cells and thus hearing. If the round window were to be absent or rigidly fixed (as can happen in some congenital abnormalities), the stapes footplate would be pushing incompressible fluid against the unyielding walls of the cochlea. It would therefore not move to any useful degree leading to a hearing loss of about 60dB. This is, unsurprisingly, the same as for conditions where the stapes itself is fixed, such as otosclerosis.
Round window | Function
For example, the lower branch of the squamosal bone is shortened to offset the tall dorsal process of quadratojugal which connects to it. On the other hand, the rear branch jugal bone lengthens to fill some of the space left by the shortening of the anterior process of the quadratojugal. In archosauriforms, the jugal even re-encloses the lower temporal fenestra. The stapes are long, thin, and solid, without a perforating hole (stapedial foramen) present in the more robust stapes of other reptiles.
Archosauromorpha | Skull
The stapes, the bone transmitting sound waves from the eardrum to the middle ear, is elongated and not pierced by a foramen. Pterygoid teeth are typically lacking.
Ichthyosaur | Skull
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.
Ossicles | Clinical relevance
The vestibule is somewhat oval in shape, but flattened transversely; it measures about 5 mm from front to back, the same from top to bottom, and about 3 mm across. In its lateral or tympanic wall is the oval window (fenestra vestibuli), closed, in the fresh state, by the base of the stapes and annular ligament. On its medial wall, at the forepart, is a small circular depression, the recessus sphæricus, which is perforated, at its anterior and inferior part, by several minute holes (macula cribrosa media) for the passage of filaments of the acoustic nerve to the saccule; and behind this depression is an oblique ridge, the crista vestibuli, the anterior end of which is named the pyramid of the vestibule.
Vestibule of the ear | Structure
Within mammals and other synapsids the columella has evolved into the stapes, a homologous bone within the newly evolved inner ear. As the tympanic cavity evolved to reduce in size, the columella shortened in length. The stirrup-shaped articular processes of the columella inspired a new name for this auditory ossicle, the stapes. The auditory ossicles continue to function in conducting transmitting sound through the auditory pathway; however, they have lost their function in conducting low frequency ground vibrations. Later-arising reptiles with columella likely evolved stronger limbs and a more crawling posture, which removed the body from the ground and prevented the transmission of ground-conducted sounds.
Columella (auditory system) | Homology in mammals
The stapes remained in contact with the quadrate bone, but functioned as auditory ossicles rather than supports for the brain case. As a result, the quadrate bones of therapsids likely had a dual function in both the jaw joint and auditory system.
Evolution of mammalian auditory ossicles | Early therapsid jaws and ears
Air vibrations could not set up pulsations through the skull as in a proper auditory organ. The spiracle was retained as the otic notch, eventually closed in by the tympanum, a thin, tight membrane. The hyomandibula of fish migrated upwards from its jaw supporting position, and was reduced in size to form the stapes. Situated between the tympanum and braincase in an air-filled cavity, the stapes was now capable of transmitting vibrations from the exterior of the head to the interior. Thus the stapes became an important element in an impedance matching system, coupling airborne sound waves to the receptor system of the inner ear.
Tetrapod | Hearing
The ossicles are suspended in the head and loosely coupled to the skull. When the head moves, the ossicles move out of phase with the head, but still follow the same cyclic motion. This causes the stapes to move in and out of the oval window. When vibrations come from the mastoid, inertial bone-conduction is greatest below 800 Hz. Putting the bone vibrator on the forehead instead of the mastoid does not significantly create this affect.
Bone conduction auditory brainstem response | Inertial bone-conduction
All of the ossicles move as a unit. The incudostapedial joint lies between the long leg (long crus or crus longum incudis) and the head of the stapes (caput stapedis). When the eardrum is moved inward due to sound vibrations, transferred through the outer ear, it transmits to the malleus and then to the incus via the incudomalleolar joint. The long leg (long crus or crus longum incudis) moves with the rest of the incus and a small knob, the lenticular process, articulates with the head of the stapes. The stapes then transfers the vibration to oval window.
Incudostapedial joint | Introduction
However, they were too incompletely preserved to estimate the light sensitivity of the eyes. The footplates of the bony stapes are large, associated with hearing low-frequency sounds underground, although its inner-ear is not as specialised as "Kawingasaurus".
Kembawacela | Burrowing
The stapes transmits sound waves to the inner ear through the oval window, a flexible membrane separating the air-filled middle ear from the fluid-filled inner ear. The round window, another flexible membrane, allows for the smooth displacement of the inner ear fluid caused by the entering sound waves.
Hearing | Middle ear
Vibrations in the middle ear are received via the tympanic membrane. The malleus, resting on the membrane, conveys vibrations to the incus. This in turn conveys vibrations to the stapes.
Incus | Function
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.
Stapes | Development
In advanced cynodonts, including the mammaliaforms, have lost the quadratojugal, with the diminutive quadrate connecting to the stapes to function as a hearing structure. In modern mammals, the quadrate bone evolves to become the incus, one of the ossicles of the middle ear. This is an apomorphy of the mammalian clade, and is used to identify the fossil transition to mammals.
Quadratojugal bone | In mammals
The "stapes" (stirrup) ossicle bone of the middle ear transmits vibrations to the "fenestra ovalis" (oval window) on the outside of the cochlea, which vibrates the perilymph in the "vestibular duct" (upper chamber of the cochlea). The ossicles are essential for efficient coupling of sound waves into the cochlea, since the cochlea environment is a fluid–membrane system, and it takes more pressure to move sound through fluid–membrane waves than it does through air; a pressure increase is achieved by the area ratio of the tympanic membrane to the oval window, resulting in a pressure gain of about 20× from the original sound wave pressure in air.
Cochlea | Hearing
In mammals, the articular and quadrate bones have migrated to the middle ear and are known as the malleus and incus. Along with the stapes, these are known as the ossicles and are a defining characteristic of mammals.
Quadrate bone | Function in mammals
The stapedius dampens the vibrations of the stapes by pulling on the neck of that bone. As one of the muscles involved in the acoustic reflex it prevents excess movement of the stapes, helping to control the amplitude of sound waves from the general external environment to the inner ear.
Stapedius muscle | Function
It is occupied by the base of the stapes, the circumference of which is fixed by the annular ligament to the margin of the foramen.
Oval window | Introduction
The incus is the second of the ossicles, three bones in the middle ear which act to transmit sound. It is shaped like an anvil, and has a long and short crus extending from the body, which articulates with the malleus. The short crus attaches to the posterior ligament of the incus. The long crus articulates with the stirrup at the lenticular process. The superior ligament of the incus attaches at the body of the incus to the roof of the tympanic cavity.
Incus | Structure
Evolution of the columella is closely related to the evolution of the jaw joint. It is an ancestral homolog of the stapes, and is derived from the hyomandibular bone of fishes. As the columella is derived from the hyomandibula, many of its functional relationships remain the same. The columella resides in the air-filled tympanic cavity of the middle ear. The footplate, or proximal end of the columella, rests in the oval window. Sound is conducted through the oval window to the interior of the otic capsule. This motion ultimately stimulates sensory cells in the inner ear. In the transition of tetrapods from sea to land, the earliest appearance of functional columella appeared in temnospondyls.
Columella (auditory system) | Evolution
These are the most unusual of the braincase bones, and were previously misidentified as stapes. While they are not stapes, it is difficult to be certain what they are. As mentioned, they are sutured to the tubera basioccipitalia, and so could not have moved freely, meaning that they were not bones for the transmission of sound in this manner. Medially, they are sutured to the posterodorsal margins of the tubera basioccipitalia by a strongly serrate and partially intergrown suture. The posterior surface of this forms a steeply inclined trough running from the suture to the distal extremity of the paraoccipital process.
Phantomosaurus | Opisthotic bones
This vibration is transmitted along the incus and stapes to the oval window. Two small muscles, the tensor tympani and stapedius, also help modulate noise. The two muscles reflexively contract to dampen excessive vibrations. Vibration of the oval window causes vibration of the endolymph within the vestibule and the cochlea. The inner ear houses the apparatus necessary to change the vibrations transmitted from the outside world via the middle ear into signals passed along the vestibulocochlear nerve to the brain. The hollow channels of the inner ear are filled with liquid, and contain a sensory epithelium that is studded with hair cells.
Ear | Hearing
The basilar membrane and the hair cells of the cochlea function as a sharply tuned frequency analyzer. Sound is transmitted to the inner ear via vibration of the tympanic membrane, leading to movement of the middle ear bones (malleus, incus, and stapes). Movement of the stapes on the oval window generates a pressure wave in the perilymph within the cochlea, causing the basilar membrane to vibrate. Sounds of different frequencies vibrate different parts of the basilar membrane, and the point of maximal vibration amplitude depends on the sound frequency. As the basilar membrane vibrates, the hair cells attached to this membrane are rhythmically pushed up against the tectorial membrane, bending the hair cell stereocilia.
Electrocochleography | Cochlear physiology
An alisphenoid strut separates two foramina (openings) at the base of the skull, the buccinator-masticatory foramen and the foramen ovale accessorium. The pattern of grooves and foramina on the head indicates that the circulation of the arteries in the head of "T. ucucha" follows the primitive pattern. The tegmen tympani, the roof of the tympanic cavity, overlaps the suspensory process of the squamosal bone. At the back of the mandible (lower jaw), there is a capsular process to receive the root of the lower incisor, which is absent in "T. hylophilus".
Thomasomys ucucha | Description
In reptiles, sound is transmitted to the inner ear by the stapes (stirrup) bone of the middle ear. This is pressed against the oval window, a membrane-covered opening on the surface of the vestibule. From here, sound waves are conducted through a short perilymphatic duct to a second opening, the round window, which equalizes pressure, allowing the incompressible fluid to move freely. Running parallel with the perilymphatic duct is a separate blind-ending duct, the lagena, filled with endolymph. The lagena is separated from the perilymphatic duct by a basilar membrane, and contains the sensory hair cells that finally translate the vibrations in the fluid into nerve signals.
Inner ear | The cochlear system
The bony palate is short, with its posterior end often located between the third molars. The alisphenoid strut, an extension of the alisphenoid bone of the skull that separates two foramina (openings) in the skull, is present in some individuals. The mastoid bone usually contains some openings. In the holotype, the head and body length is 130 mm, the tail length is 160 mm, the hindfoot length (without claws) is 31 mm, the ear length is 27 mm, and the skull length is 35.7 mm.
Nephelomys levipes | Introduction
The anular ligament, a ring-like structure that forms a seal between the end of the stapes and the rim of the vestibular foramen, was probably held in place by cartilage. The transfer of sound between the thin bony plate and the vestibular foramen in "Glanosuchus" was not as effective as it is in mammals, meaning that the animal had a less acute sense of hearing.
Glanosuchus | Hearing
The middle ear contains three tiny bones known as the ossicles: "malleus", "incus", and "stapes". The ossicles were given their Latin names for their distinctive shapes; they are also referred to as the "hammer", "anvil", and "stirrup", respectively. The ossicles directly couple sound energy from the eardrum to the oval window of the cochlea. While the stapes is present in all tetrapods, the malleus and incus evolved from lower and upper jaw bones present in reptiles. The ossicles are classically supposed to mechanically convert the vibrations of the eardrum into amplified pressure waves in the fluid of the cochlea (or inner ear), with a lever arm factor of 1.3.
Middle ear | Ossicles
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.
Stapes | Variation
The transfer function of this complex mechanical system under physiological conditions is modulated by the action of two small muscles of the middle ear, the tensor tympani, and stapedius. The tensor tympani arises from the cartilaginous portion of the auditory tube and the osseous canal of the sphenoid and, having sharply bent over the extremity of the septum, attaches to the manubrium of the malleus (hammer); its contraction pulls the malleus medially, away from the tympanic membrane, which tenses the membrane. The stapedius, which emerges from the posterior wall of the tympanic cavity of the middle ear and inserts into the neck of the stapes (stirrup), prevents excess movements of the stapes by pulling it away from the oval window.
Non-invasive measurement of intracranial pressure | Tympanic membrane displacement
The tympanic cavity and eustachian tube are derived from the first pharyngeal pouch (a cavity lined by endoderm). The distal part of the cleft, the tubotympanic recess, widens to create the tympanic cavity. The proximal part of the cleft remains narrow and creates the eustachian tube. The bones of the middle ear, the ossicles, derive from the cartilages of the pharyngeal arches. The malleus and incus derive from the cartilage of the first pharyngeal arch, whereas the stapes derives from the cartilage of the second pharyngeal arch.
Human embryonic development | Middle ear
The stapedius emerges from a pinpoint foramen in the apex of the pyramidal eminence (a hollow, cone-shaped prominence in the posterior wall of the tympanic cavity), and inserts into the neck of the stapes.
Stapedius muscle | Structure
This gain is a form of impedance matching – to match the soundwave travelling through air to that travelling in the fluid–membrane system. At the base of the cochlea, each "duct" ends in a membranous portal that faces the middle ear cavity: The "vestibular duct" ends at the oval window, where the footplate of the stapes sits. The footplate vibrates when the pressure is transmitted via the ossicular chain. The wave in the perilymph moves away from the footplate and towards the helicotrema. Since those fluid waves move the cochlear partition that separates the ducts up and down, the waves have a corresponding symmetric part in perilymph of the "tympanic duct", which ends at the round window, bulging out when the oval window bulges in.
Cochlea | Hearing
The earliest mammals were generally small animals, and were likely nocturnal insectivores. This suggests a plausible source of evolutionary pressure: with these small bones in the middle ear, a mammal has extended its range of hearing for higher-pitched sounds which would improve the detection of insects in the dark. The evidence that the malleus and incus are homologous to the reptilian articular and quadrate was originally embryological, and since this discovery an abundance of transitional fossils has both supported the conclusion and given a detailed history of the transition. The evolution of the stapes (from the columella) was an earlier and distinct event.
Evolution of mammalian auditory ossicles | Early mammals
The mammalian jaw joint is composed of different skull bones, including the dentary (the lower jaw bone which carries the teeth) and the squamosal (another small skull bone). In mammals, the quadrate and articular bones have evolved into the incus and malleus bones in the middle ear. The mammalian middle ear contains three tiny bones known as the ossicles: malleus, incus, and stapes. The ossicles are a complex system of levers whose functions include: reducing the amplitude of the vibrations; increasing the mechanical force of vibrations; and thus improving the efficient transmission of sound energy from the eardrum to the inner ear structures.
Evolution of mammalian auditory ossicles | Defining characteristic of mammals
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.
Stapes | Clinical relevance
In modern amniotes (including mammals), the middle ear collects airborne sounds through an eardrum and transmits vibrations to the inner ear via thin cartilaginous and ossified structures. These structures usually include the stapes (a stirrup-shaped auditory ossicle). Early tetrapods likely did not possess eardrums. Eardrums appear to have evolved independently three to six times. In basal members of the 3 major clades of amniotes (synapsids, eureptiles, and parareptiles) the stapes bones are relatively massive props that support the braincase, and this function prevents them from being used as part of the hearing system. However, there is increasing evidence that synapsids, eureptiles and parareptiles developed eardrums connected to the inner ear by stapes during the Permian.
Evolution of mammalian auditory ossicles | Early tetrapod and amniote ears
The annular stapedial ligament (also called the stapediovestibular joint) is a ring of fibrous soft tissue that connects the base of the stapes to the oval window of the inner ear. Calcification and hardening of the annular ligament of the stapes (Otosclerosis) is a common cause of adult deafness.
Annular ligament of stapes | Introduction
Such structures include a shelf at the rear of the surangular and a thick articular bone which has a tall retroarticular process with an inner prong pierced by a "chorda tympani" foramen.
Prestosuchus | Skull
As the dentary bone of the lower jaw continued to enlarge during the Triassic, the older quadrate-articular joint fell out of use. Some of the bones were lost, but the quadrate, the articular, and the angular bones became free-floating and associated with the stapes. This occurred at least twice in the mammaliformes. The multituberculates had jaw joints that consisted of only the dentary and squamosal bones, and the quadrate and articular bones were part of the middle ear. Other features of their teeth, jaws and skulls are significantly different from those of mammals.
Evolution of mammalian auditory ossicles | Fossil evidence for mammal-like jaws and ears
The head of the malleus (caput mallei) moves with it and transfers energy/movement to the corpus of the incus (corpus incudis), which is located directly behind. The sound vibrations are then transferred to the stapes (stirrup) through the incudostapedial joint.
Incudomalleolar joint | Introduction
This system had evolved independently within several different amphibian lineages. The impedance matching ear had to meet certain conditions to work. The stapes had to be perpendicular to the tympanum, small and light enough to reduce its inertia, and suspended in an air-filled cavity. In modern species that are sensitive to over 1 kHz frequencies, the footplate of the stapes is 1/20th the area of the tympanum. However, in early amphibians the stapes was too large, making the footplate area oversized, preventing the hearing of high frequencies. So it appears they could only hear high intensity, low frequency sounds—and the stapes more probably just supported the brain case against the cheek.
Tetrapod | Hearing
Its postero-superior surface is concave, and forms the anterior wall, the floor, and part of the posterior wall of the bony ear canal. Medially, it presents a narrow furrow, the "tympanic sulcus", for the attachment of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa, and is in contact with the retromandibular part of the parotid gland.
Tympanic part of the temporal bone | Surfaces
The dorsal process of the stapes in "Theriognathus" is greatly reduced or entirely absent. The dentary is short, shaped like a banana, and continuously tapers anteriorly to a narrow edge. The dentarys’ lateral surface is smooth. The posterodorsal terminal end of the coronoid process is more rounded, and the dorsal extent terminates below the middle of the orbit in adults. The postdentary bones are reduced to form a free standing coronoid process. The reflected lamina is spade shaped and does not extend below the dentary The area between left and right dentaries remains relatively long and narrow just posterior to symphyseal region.
Theriognathus | Lower jaw
Sound waves travel through the ear canal and hit the tympanic membrane, or eardrum. This wave information travels across the air-filled middle ear cavity via a series of delicate bones: the malleus (hammer), incus (anvil) and stapes (stirrup). These ossicles act as a lever, converting the lower-pressure eardrum sound vibrations into higher-pressure sound vibrations at another, smaller membrane called the oval window or vestibular window. The manubrium (handle) of the malleus articulates with the tympanic membrane, while the footplate (base) of the stapes articulates with the oval window. Higher pressure is necessary at the oval window than at the typanic membrane because the inner ear beyond the oval window contains liquid rather than air.
Auditory system | Middle ear
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".
Ossicles | Structure
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 an eardrum. It is an evolutionary homolog of the stapes, one of the auditory ossicles in mammals. In many species, the extracolumella is a cartilagenous structure that grows in association with the columella. During development, the columella is derived from the dorsal end of the hyoid arch.
Columella (auditory system) | Introduction
"Glanosuchus" represents an early stage in the development of the mammalian middle ear. Modern mammals have three bones in the middle ear (the malleus, incus, and stapes) that transfer sound energy from the eardrum to the fluid of the inner ear. The malleus and incus of mammals developed from the articular and quadrate of early therapsids. Studies of the bones of "Glanosuchus" show that it had a very thin plate of bone that acted as an eardrum, receiving sounds and transferring them to a small air-filled cavity. The stapes and vestibular foramen (the hole that connects the middle and inner ears) are preserved in one specimen of "Glanosuchus" that was examined by grinding away cross sections of the skull.
Glanosuchus | Hearing
The inner end of the external acoustic meatus is closed, in the recent state, by the tympanic membrane; the upper limit of its outer orifice is formed by the posterior root of the zygomatic process, immediately below which there is sometimes seen a small spine, the suprameatal spine also called the spine of Henle, situated at the upper and posterior part of the orifice.
Suprameatal spine | Introduction
"Styloichthys" is characterized by large pores on the cosmine surface. These pores are often spoon-shaped and arranged in parallel grooves. There is a jagged margin between ethmosphenoid and otoccipital shields, an otoccipital with a wide flat surface carrying no vestibular fontanelle. The snout bends sharply downward and is slightly concave. The lower jaw has a ventrally protruding flange formed by prearticular and meckelian bone. Also characteristic of "Styloichthys" is the lyre-shaped trajectory of the supraorbital canal, a fenestra ventralis, small internasal cavities, three coronoids in the lower jaw, an eyestalk and a slender postorbital pila which connects the basipterygoid process and the side of the braincase wall.
Styloichthys | Description
CHL in otosclerosis is caused by two main sites of involvement of the sclerotic (or scar-like) lesions. The best understood mechanism is fixation of the stapes footplate to the oval window of the cochlea. This greatly impairs movement of the stapes and therefore transmission of sound into the inner ear ("ossicular coupling"). Additionally the cochlea's round window can also become sclerotic, and in a similar way impair movement of sound pressure waves through the inner ear ("acoustic coupling"). Conductive hearing loss is usually concomitant with impingement of abnormal bone on the stapes footplate. This involvement of the oval window forms the basis of the name fenestral otosclerosis.
Otosclerosis | Pathophysiology
This is connected indirectly with the eardrum via a mostly cartilaginous extracolumella and medially to the inner-ear spaces via a widened footplate in the fenestra ovalis. The columella is an evolutionary derivative of the bone known as the hyomandibula in fish ancestors, a bone that supported the skull and braincase. The structure of the middle ear in living amphibians varies considerably and is often degenerate. In most frogs and toads, it is similar to that of reptiles, but in other amphibians, the middle ear cavity is often absent. In these cases, the stapes either is also missing or, in the absence of an eardrum, connects to the quadrate bone in the skull, although, it is presumed, it still has some ability to transmit vibrations to the inner ear.
Middle ear | Other animals
The oval window (or fenestra vestibuli) 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 inner ear. The oval window is the intersection of the middle ear with the inner ear and is directly contacted by the stapes; by the time vibrations reach the oval window, they have been amplified over 10 times from what they were when they contacted the tympanic membrane, a testament to the amplifying power of the middle ear. It is a reniform (kidney-shaped) opening leading from the tympanic cavity into the vestibule of the internal ear; its long diameter is horizontal and its convex border is upward.
Oval window | Introduction
The opening to the meatus is called the porus acusticus internus or internal acoustic opening. It is located inside the posterior cranial fossa of the skull, near the center of the posterior surface of the petrous part of the temporal bone. The size varies considerably. Its outer margins are smooth and rounded. The canal which comprises the internal auditory meatus is short (about 1 cm) and runs laterally into the bone. The lateral (outer) aspect of the canal is known as the fundus. The fundus is subdivided by two thin crests of bone to form three separate canals, through which course the facial and vestibulocochlear nerve branches.
Internal auditory meatus | Structure
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.
Ossicles | Function
While the basic structure of the inner ear in lepidosaurs (lizards and snakes), archosaurs (birds and crocodilians) and mammals is similar, and the organs are considered to be homologous, each group has a unique type of auditory organ. The hearing organ arose within the lagenar duct of stem reptiles, lying between the saccular and lagenar epithelia. In lepidosaurs, the hearing organ, the basilar papilla, is generally small, with at most 2000 hair cells, whereas in archosaurs the basilar papilla can be much longer (>10mm in owls) and contain many more hair cells that show two typical size extremes, the short and the tall hair cells.
Evolution of the cochlea | Comparative anatomy
Caudal to what will eventually become the stapes, Reichert's cartilage also forms the styloid process of the temporal bone. The cartilage between the hyoid bone and styloid process will not remain as development continues, but its perichondrium will eventually form the stylohyoid ligament.
Pharyngeal arch | Reichert's cartilage
The outer ear funnels sound vibrations to the eardrum, increasing the sound pressure in the middle frequency range. The middle-ear ossicles further amplify the vibration pressure roughly 20 times. The base of the stapes couples vibrations into the cochlea via the oval window, which vibrates the perilymph liquid (present throughout the inner ear) and causes the round window to bulb out as the oval window bulges in. Vestibular and tympanic ducts are filled with perilymph, and the smaller cochlear duct between them is filled with endolymph, a fluid with a very different ion concentration and voltage. Vestibular duct perilymph vibrations bend organ of Corti outer cells (4 lines) causing prestin to be released in cell tips.
Auditory system | System overview
In the tetrapod and higher clades from the lower-middle Famennian there are several defining changes on the basis of anatomy of "Ichthyostega", "Tulerpeton", and "Acanthostega". In the cranium, there is a stapes derived from the hyomandibular of fishes; a single bilateral pair of nasal bones, and a fenestra ovalis in the otic capsule of the braincase. The opening of the otic wall of the braincase can be considered a paedomorphic feature for tetrapods and is linked to the stapes functionally. The stapes was thought to be just a structural support between the palate and the stapedial plate of the braincase.
Skeletal changes of organisms transitioning from water to land | Head changes in aquatic tetrapods
This anatomical structure processes incoming auditory information.
Richard L. Heschl | Biography
Its anterior wall and floor and the lower part of its posterior wall are formed by the tympanic part; the roof and upper part of the posterior wall by the squama. Its inner end is closed, by the tympanic membrane which originates from the tympanic sulcus; the upper limit of its outer orifice is formed by the posterior root of the zygomatic process, immediately below which there is sometimes seen a small spine, the "suprameatal spine", situated at the upper and posterior part of the orifice. The auditory bulla (pl. bullae) is a hollow bony structure on the ventral, posterior portion of the skull that encloses parts of the middle and inner ear.
Tympanic part of the temporal bone | Ear canal
Over the course of the evolution of mammals, one bone from the lower and one from the upper jaw (the articular and quadrate bones) lost their purpose in the jaw joint and migrated to the middle ear. The shortened columella connected to these bones within the middle ear to form a chain of three bones, the ossicles, which serve to effectively transmit air-based vibrations and facilitate more acute hearing.
Evolution of mammalian auditory ossicles | Introduction
In "Anoualerpeton priscus", the suprapalatal fossa lies in the medial edge of the external nasal opening. In "Anoualerpeton unicus", however, it lies further mediad, outside the border of the external nasal opening.
Anoualerpeton | Morphology
The stapes is commonly described as having been discovered by the professor Giovanni Filippo Ingrassia 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 (), an example of a late Latin word, probably created in mediaeval times from "to stand" (), as stirrups did not exist in the early Latin-speaking world.
Stapes | History
Surgery may be complicated by a persistent stapedial artery, fibrosis-related damage to the base of the bone, or obliterative otosclerosis, resulting in obliteration of the base.
Stapes | Clinical relevance
The oval window and the ear vestibule form a funnel-shaped recess penetrating deep into the ear zone and having a wide exit on the side wall of the braincase. The inner ear is large with robust semicircular canals.
Timurlengia | Description
The ability of the tympanum and stapes to effectively transmit vibrations is called impedance matching. Early tetrapods like temnospondyls have thick stapes with poor impedance matching, so it is now thought that they were not used for hearing. Instead, these thick stapes may have functioned to support the tissue that covers the otic notch. Early temnospondyls, like "Dendrerpeton", could not hear airborne sound but would have been able to detect vibration in the ground. Later temnospondyls like "Doleserpeton" had otic regions adapted to hearing. "Doleserpeton" has a structure in the inner ear called the perilymphatic duct, which is also seen in frogs and is associated with hearing.
Temnospondyli | Hearing
Studies have shown that ear bones in mammal embryos are attached to the dentary, which is part of the 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.
Ossicles | Development
The bony part (1/3) nearest to the middle ear is made of bone and is about 12 mm in length. It begins in the anterior wall of the tympanic cavity, below the septum canalis musculotubarii, and, gradually narrowing, ends at the angle of junction of the squamous and the petrous parts of the temporal bone, its extremity presenting a jagged margin which serves for the attachment of the cartilaginous part.
Eustachian tube | Bony part
From medial to lateral, the transverse (falciform) crest first divides the meatus into superior and inferior sections; a second vertical crest (Bill's bar, named by William F. House) then divides the upper passage into anterior and posterior sections. Although there are three osseous canals, the fundus is conceptually divided more commonly into four quadrant areas according to the four major nerve branches of the inner ear:
Internal auditory meatus | Structure
The pterygoids and palatines were seemingly toothless, although this observance may be due to poor preservation. The tip of each ectopterygoid expands into a fan-shaped structure, and the suborbital fenestra is very short.
Prolacertoides | Description
The quadrate is also smooth, and it encloses a circular hole (only visible from behind) along its contact with the quadratojugal. Part of the nasal cavity was filled in by sediment, showing that the olfactory bulbs were separated at the midline. The braincase is incomplete, only preserving the parabasisphenoid (the bone which forms the base of the braincase). As with other archosaurs, the rear lower part of the braincase possessed two different pairs of large, rounded plates: The basipterygoid processes (which are positioned at the base of the braincase and contact the roof of the mouth) and the basitubera (which are positioned further up and do not contact any bone, acting as levers for the "musculi recti capitis anteriores" that make the head nod).
Venaticosuchus | Description
In the middle ear, the energy of pressure waves is translated into mechanical vibrations by the three auditory ossicles. Pressure waves move the tympanic membrane which in turns moves the malleus, the first bone of the middle ear. The malleus articulates to incus which connects to the stapes. The footplate of the stapes connects to the oval window, the beginning of the inner ear. When the stapes presses on the oval window, it causes the perilymph, the liquid of the inner ear to move. The middle ear thus serves to convert the energy from sound pressure waves to a force upon the perilymph of the inner ear.
Inner ear | Vestibular and cochlear systems
This inclusion is based on the fusion of the frontals as well as the inclusion of the prootic bone in the "recessus scalae tympani", a structure of the inner ear. They also found that a number of characteristics were shared by Barbatteiidae and Teiidae, including the overlap of the squamosal by the postorbital; the origin of the temporal muscles on the upper portion of the parietals, which is overlapped by the contact between the parietals and the ectopterygoid bones; and the weakly-developed shelf on the inside of the tooth row. The phylogenetic tree is reproduced below.
Oardasaurus | Classification
The length of the skull can range from 84mm to 104mm for midline length. to Through the analysis of the middle ear region of "Dendrerpeton acadianum", it could be determined that this taxa has a tympanic ear that is not there as a means of support for the palatoquadrate, but rather the positioning of the stapes indicates that it is used for the movement of sound. This morphology demonstrates "Dendrerpeton" having a hearing system that mimics that of anurans. This was contrary to what was previously thought, which was that it had a "squamosal embayment" rather than an otic notch.
Dendrerpeton | Skull and Skeleton
Structurally, the endocranium consists of a boxlike shape, open at the top. The posterior margin exhibit the "foramen magnum", an opening for the spinal cord. The floor of the endocranium has several paired openings for the cranial nerves, and the anterior margin holds a spongy construction, allowing for the external nasal nerves to pass through. All bones of the structure derive from the cranial neural crest during fetal development.
Endocranium | Structure
An forward-directed extension of the supratemporal formed the inner-rear edge of the supratemporal fenestra, an opening through the skull roof behind the eyes. The parietal, which would have formed the inner margin of the supratemporal fenestra, had a complex front margin that was interdigitating with either the frontal or postfrontal bones, which are not preserved in the known specimens. The quadrate bone, which connected to the lower jaw to form the jaw joint, was C-shaped in side view. Two probable hyoid bones (tongue bones) are preserved with specimen SNHM1284-R; these bones were rod-like, with one end spatula-shaped. The stapes (bone in the ear region that is used for hearing) had a shaft that was more slender than in any other ichthyosaur, and its head was large and square—these features are regarded an autapomorphy (unique feature) and serve to distinguish the genus from related genera.
Acamptonectes | Skull
Since the effective vibratory area of the eardrum is about 14 fold larger than that of the oval window, the sound pressure is concentrated, leading to a pressure gain of at least 18.1. The eardrum is merged to the malleus, which connects to the incus, which in turn connects to the stapes. Vibrations of the stapes footplate introduce pressure waves in the inner ear. There is a steadily increasing body of evidence that shows that the lever arm ratio is actually variable, depending on frequency. Between 0.1 and 1 kHz it is approximately 2, it then rises to around 5 at 2 kHz and then falls off steadily above this frequency.
Middle ear | Ossicles
The utricle is larger than the saccule and is of an oblong form, compressed transversely, and occupies the upper and back part of the vestibule, lying in contact with the recessus ellipticus and the part below it. The macula of utricle is a thickening in the wall of the utricle where the epithelium contains vestibular hair cells that allows a person to perceive changes in latitudinal acceleration as well as effects of gravity. The gelatinous layer and the statoconia together are referred to as the otolithic membrane, where the tips of the stereocilia and kinocilium are embedded. When the head is tilted such that gravity pulls on the statoconia the gelatinous layer is pulled in the same direction also causing the sensory hairs to bend.
Utricle (ear) | Structure
As evolution later attached the cranium of terrestrial vertebrates to the rest of the skull, the hyomandibula lost its supportive function and became an interior organ, the stapes, and thus its secondary function had become its primary function.
Hyomandibula | Evolutionary context
The round window is situated below (inferior to) and a little behind (posterior to) the oval window, from which it is separated by a rounded elevation, the promontory. It is located at the bottom of a funnel-shaped depression (the round window niche) and, in the macerated bone, opens into the cochlea of the internal ear; in the fresh state it is closed by a membrane, the secondary tympanic membrane (Latin: "membrana tympani secundaria", or "membrana fenestrae cochleae") or round window membrane, which is a complex saddle point shape. The visible central portion is concave (curved inwards) toward the tympanic cavity and convex (curved outwards) toward the cochlea; but towards the edges, where it is hidden in the round window niche, it curves the other way.
Round window | Structure
The scapes are short, measuring , and the pedicel (the second segment of the antenna) is The flagellomeres vary in length, ranging between . The clypeus is shallow and measures (when excluding the denticles). It is broad, and the distance between its lateral-most denticles is . It is also more concave-shaped than it is straight. The oral margin of the clypeus is lined with a row of 30 denticles, which are peg-shaped. They also have rounded apices. The row of clypeal margin denticles is composed of two short rows. Each row is composed of 15 denticles each. The mandibles are short and barely overlap medially.
Zigrasimecia | "Z. tonsora"
This refers to the form of the corolla, which is composed of three membranous bracts that create a profile similar to that of a human ear.
Otanthus | Introduction
The walls of the hollow cochlea are made of bone, with a thin, delicate lining of epithelial tissue. This coiled tube is divided through most of its length by an inner membranous partition. Two fluid-filled outer spaces ("ducts" or "scalae") are formed by this dividing membrane. At the top of the snailshell-like coiling tubes, there is a reversal of the direction of the fluid, thus changing the vestibular duct to the tympanic duct. This area is called the helicotrema. This continuation at the helicotrema allows fluid being pushed into the vestibular duct by the oval window to move back out via movement in the tympanic duct and deflection of the round window; since the fluid is nearly incompressible and the bony walls are rigid, it is essential for the conserved fluid volume to exit somewhere.
Cochlea | Microanatomy
In fact it has been shown that the coccyx may consist of up to five separate bony segments, the most common configuration being two or three segments.
Coccyx | Structure
The basal margin is crenulate. The columella is tuberculose, above twisted plicate, below obsoletely truncate. The white umbilical area is spirally plicate with a crenulate margin. The thin parietal callus is wrinkled.
Clanculus kraussii | Description
In addition, a structure composed of fused neural spines form the dorsalmost part of the Weberian apparatus. Together, the structure interacts anteriorly with the lagenar otolith set within the skull and posteriorly with the swim bladder via the pleural rib. Postero-ventrally, it is the tripus, the os suspensorium and the third rib that interact directly with the anterior chamber of the swim bladder. The Weberian apparatus functions by transmitting auditory signals straight from the gas bladder, through the Weberian ossicles and then straight into the labyrinth structures of the inner ear. The structure essentially acts as an amplifier of sound waves that would otherwise be only slightly perceivable by the inner ear structure alone.
Weberian apparatus | Structural anatomy and function
The posterior surface forms the anterior part of the posterior cranial fossa of the base of the skull, and is continuous with the inner surface of the mastoid portion. Near the center is a large orifice, the internal acoustic opening, the size of which varies considerably; its margins are smooth and rounded, and it leads into the internal auditory meatus a short canal, about 1 cm. in length, which runs lateralward. It transmits the facial and acoustic nerves and the internal auditory branch of the basilar artery. The lateral end of the canal is closed by a vertical plate, which is divided by a horizontal crest, the falciform crest, into two unequal portions.
Petrous part of the temporal bone | Posterior surface
The movement of the ossicles may be stiffened by two muscles. The stapedius muscle, the smallest skeletal muscle in the body, connects to the stapes and is controlled by the facial nerve; the tensor tympani muscle is attached to the upper end of the medial surface of the handle of malleus and is under the control of the medial pterygoid nerve which is a branch of the mandibular nerve of the trigeminal nerve. These muscles contract in response to loud sounds, thereby reducing the transmission of sound to the inner ear. This is called the acoustic reflex.
Middle ear | Muscles
On it is a curved fissure, the hiatus semilunaris, limited below by the edge of the uncinate process of the ethmoid and above by an elevation named the bulla ethmoidalis; the middle ethmoidal cells are contained within this bulla and open on or near to it. Through the hiatus semilunaris the meatus communicates with a curved passage termed the infundibulum, which communicates in front with the anterior ethmoidal cells and in rather more than fifty percent of skulls is continued upward as the frontonasal duct into the frontal air-sinus; when this continuity fails, the frontonasal duct opens directly into the anterior part of the meatus.
Nasal meatus | Structure
The evolution of mammalian auditory ossicles was an evolutionary event 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. The ossicles evolved from skull bones present in most tetrapods, including the reptilian lineage. The reptilian quadrate bone, articular bone, and columella evolved into the mammalian incus, malleus, and stapes (anvil, hammer, and stirrup), respectively. In reptiles, the eardrum is connected to the inner ear via a single bone, the columella, while the upper and lower jaws contain several bones not found in mammals.
Evolution of mammalian auditory ossicles | Introduction
Neural crest cells will migrate rostral and caudal to the placode. The general sequence in formation of the otic vesicle is relatively conserved across vertebrates, although there is much variation in timing and stages. Patterning during morphogenesis into the distinctive inner ear structures is determined by homeobox transcription factors including PAX2, DLX5 and DLX6, with the former specifying for ventral otic vesicle derived auditory structures and the latter two specifying for dorsal vestibular structures.
Otic vesicle | Introduction
"D. fallai" use an abdomino-femoral mechanism to produce sound by rubbing their hind legs against the tergites on their abdomen. Their specific type of mechanism is called Tergo-tergal stridulatory mechanism. They have one large crescent shaped file ridge on their second tergite plate, as well as many tiny spiny pegs on the ventro-posterior portion of their tergite and several additional blunt pegs that are dorsally faced. The leading edge of the convex crescent ridge is separated by a longitudinal groove that forms two lips. On their femur they have raised, elongated pegs that are grooved to the middle of their femur and point radially away from the femur base.
Deinacrida fallai | Sound production