The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear, 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 ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localisation. The ear develops from the first pharyngeal pouch and six small swellings that develop in the early embryo called otic placodes, which are derived from ectoderm. The ear may be affected by disease, including infection and traumatic damage. Diseases of the ear may lead to hearing loss, tinnitus and balance disorders such as vertigo, although many of these conditions may also be affected by damage to the brain or neural pathways leading from the ear. The ear has been adorned by earrings and other jewellery in numerous cultures for thousands of years, and has been subjected to surgical and cosmetic alterations.
1.1 Outer ear 1.2 Middle ear 1.3 Inner ear 1.4 Blood supply
2.1 Hearing 2.2 Balance
3.1 Inner ear 3.2 Middle ear 3.3 Outer ear
4 Clinical significance
5 Society and culture 6 Other animals
7 See also 8 References 9 External links
The eardrum as viewed from the outside using an otoscope. The outer ear ends at the eardrum, and the middle ear can be seen in the tympanic cavity behind.
The human ear consists of three parts—the outer ear, middle ear and inner ear. The ear canal of the outer ear is separated from the air-filled tympanic cavity of the middle ear by the eardrum. The middle ear contains the three small bones—the ossicles—involved in the transmission of sound, and is connected to the throat at the nasopharynx, via the pharyngeal opening of the Eustachian tube. The inner ear contains the otolith organs—the utricle and saccule—and the semicircular canals belonging to the vestibular system, as well as the cochlea of the auditory system. Outer ear Main article: Outer ear The outer ear is the external portion of the ear and includes the fleshy visible pinna (also called the auricle), the ear canal, and the outer layer of the eardrum (also called the tympanic membrane). The pinna consists of the curving outer rim called the helix, the inner curved rim called the antihelix, and opens into the ear canal. The tragus protrudes and partially obscures the ear canal, as does the facing antitragus. The hollow region in front of the ear canal is called the concha. The ear canal stretches for about 1 inch (2.5 cm). The first part of the canal is surrounded by cartilage, while the second part near the eardrum is surrounded by bone. This bony part is known as the auditory bulla and is formed by the tympanic part of the temporal bone. The skin surrounding the ear canal contains ceruminous and sebaceous glands that produce protective ear wax. The ear canal ends at the external surface of the eardrum. Two sets of muscles are associated with the outer ear: the intrinsic and extrinsic muscles. In some mammals, these muscles can adjust the direction of the pinna. In humans, these muscles have little or no effect. The ear muscles are supplied by the facial nerve, which also supplies sensation to the skin of the ear itself, as well as to the external ear cavity. The great auricular nerve, auricular nerve, auriculotemporal nerve, and lesser and greater occipital nerves of the cervical plexus all supply sensation to parts of the outer ear and the surrounding skin. The pinna consists of a single piece of elastic cartilage with a complicated relief on its inner surface and a fairly smooth configuration on its posterior surface. A tubercle, known as Darwin's tubercle, is sometimes present, lying in the descending part of the helix and corresponding to the ear-tip of mammals. The earlobe consists of areola and adipose tissue. The symmetrical arrangement of the two ears allows for the localisation of sound. The brain accomplishes this by comparing arrival-times and intensities from each ear, in circuits located in the superior olivary complex and the trapezoid bodies which are connected via pathways to both ears.
Middle ear Main article: Middle ear
The middle ear
The middle ear lies between the outer ear and the inner ear. It consists of an air-filled cavity called the tympanic cavity and includes the three ossicles and their attaching ligaments; the auditory tube; and the round and oval windows. The ossicles are three small bones that function together to receive, amplify, and transmit the sound from the eardrum to the inner ear. The ossicles are the malleus (hammer), incus (anvil), and the stapes (stirrup). The stapes is the smallest named bone in the body. The middle ear also connects to the upper throat at the nasopharynx via the pharyngeal opening of the Eustachian tube. The three ossicles transmit sound from the outer ear to the inner ear. The malleus receives vibrations from sound pressure on the eardrum, where it is connected at its longest part (the manubrium or handle) by a ligament. It transmits vibrations to the incus, which in turn transmits the vibrations to the small stapes bone. The wide base of the stapes rests on the oval window. As the stapes vibrates, vibrations are transmitted through the oval window, causing movement of fluid within the cochlea. The round window allows for the fluid within the inner ear to move. As the stapes pushes the secondary tympanic membrane, fluid in the inner ear moves and pushes the membrane of the round window out by a corresponding amount into the middle ear. The ossicles help amplify sound waves by nearly 15–20 times. Inner ear
The outer ear receives sound, transmitted through the ossicles of the middle ear to the inner ear, where it is converted to a nervous signal in the cochlear and transmitted along the vestibulocochlear nerve
Main article: Inner ear
The inner ear sits within the temporal bone in a complex cavity called
the bony labyrinth. A central area known as the vestibule contains two
small fluid-filled recesses, the utricle and saccule. These connect to
the semicircular canals and the cochlea. There are three semicircular
canals angled at right angles to each other which are responsible for
dynamic balance. The cochlea is a spiral shell-shaped organ
responsible for the sense of hearing. These structures together create
the membranous labyrinth.
The bony labyrinth refers to the bony compartment which contains the
membranous labyrinth, contained within the temporal bone. The inner
ear structurally begins at the oval window, which receives vibrations
from the incus of the middle ear. Vibrations are transmitted into the
inner ear into a fluid called endolymph, which fills the membranous
labyrinth. The endolymph is situated in two vestibules, the utricle
and saccule, and eventually transmits to the cochlea, a spiral-shaped
structure. The cochlea consists of three fluid-filled spaces: the
vestibular duct, the cochlear duct, and the tympanic duct. Hair
cells responsible for transduction—changing mechanical changes into
electrical stimuli are present in the organ of Corti in the
The blood supply of the ear differs according to each part of the ear.
The outer ear is supplied by a number of arteries. The posterior
auricular artery provides the majority of the blood supply. The
anterior auricular arteries provide some supply to the outer rim of
the ear and scalp behind it. The posterior auricular artery is a
direct branch of the external carotid artery, and the anterior
auricular arteries are branches from the superficial temporal artery.
The occipital artery also plays a role.
The middle ear is supplied by the mastoid branch of either the
occipital or posterior auricular arteries and the deep auricular
artery, a branch of the maxillary artery. Other arteries which are
present but play a smaller role include branches of the middle
meningeal artery, ascending pharyngeal artery, internal carotid
artery, and the artery of the pterygoid canal.
The inner ear is supplied by the anterior tympanic branch of the
maxillary artery; the stylomastoid branch of the posterior auricular
artery; the petrosal branch of middle meningeal artery; and the
labyrinthine artery, arising from either the anterior inferior
cerebellar artery or the basilar artery.
Main article: Hearing
The otic placode visible on this sketch of a developing embryo.
After implantation, around the second to third week the developing embryo consists of three layers: endoderm, mesoderm and ectoderm. The first part of the ear to develop is the inner ear, which begins to form from the ectoderm around the 22nd day of the embryo’s development. Specifically, the inner ear derives from two thickenings called otic placodes on either side of the head. Each otic placode recedes below the ectoderm, forms an otic pit and then an otic vesicle. This entire mass will eventually become surrounded by mesenchyme to form the bony labyrinth. Around the 33rd day of development, the vesicles begin to differentiate. Closer to the back of the embryo, they form what will become the utricle and semicircular canals. Closer to the front of the embryo, the vesicles differentiate into a rudimentary saccule, which will eventually become the saccule and cochlea. Part of the saccule will eventually give rise and connect to the cochlear duct. This duct appears approximately during the sixth week and connects to the saccule through the ductus reuniens. As the cochlear duct’s mesenchyme begins to differentiate, three cavities are formed: the scala vestibuli, the scala tympani and the scala media. Both the scala vestibuli and the scala tympani contain an extracellular fluid called perilymph. The scala media contains endolymph. A set of membranes called the vestibular membrane and the basilar membrane develop to separate the cochlear duct from the vestibular duct and the tympanic duct, respectively. Parts of the otic vesicle in turn form the vestibulocochlear nerve. These form bipolar neurons which supply sensation to parts of the inner ear (namely the sensory parts of the semicircular canals, macular of the utricle and saccule, and organ of Corti). The nerve begins to form around the 28th day.
Most of the genes responsible for the regulation of inner ear formation and its morphogenesis are members of the homeobox gene family such as Pax, Msx and Otx homeobox genes. The development of inner ear structures such as the cochlea is regulated by Dlx5/Dlx6, Otx1/Otx2 and Pax2, which in turn are controlled by the master gene Shh. Shh is secreted by the notochord. Middle ear The middle ear and its components develop from the first and second pharyngeal arches. The tympanic cavity and auditory tube develop from the first part of the pharyngeal pouch between the first two arches in an area which will also go on to develop the pharynx. This develops as a structure called the tubotympanic recess. The ossicles (malleus, incus and stapes) normally appear during the first half of fetal development. The first two (malleus and incus) derive from the first pharyngeal arch and the stapes derives from the second. All three ossicles develop from the neural crest. Eventually cells from the tissue surrounding the ossicles will experience apoptosis and a new layer of endodermal epithelial will constitute the formation of the tympanic cavity wall. Outer ear
The ear develops in the lower neck region and moves upwards as the mandible develops.
Unlike structures of the inner and middle ear, which develop from
pharyngeal pouches, the ear canal originates from the dorsal portion
of the first pharyngeal cleft. It is fully expanded by the end
of the 18th week of development. The eardrum is made up of three
layers (ectoderm, endoderm and connective tissue). The pinna
originates as a fusion of six hillocks. The first three hillocks are
derived from the lower part of the first pharyngeal arch and form the
tragus, crus of the helix, and helix, respectively. The final three
hillocks are derived from the upper part of the second pharyngeal arch
and form the antihelix, antitragus, and earlobe. The outer
ears develop in the lower neck. As the mandible forms they move
towards their final position level with the eyes.
Fluid in the middle ear cavity
Complications of otitis media that can lead to hearing loss, as seen on otoscope.
Injuries to the external ear occur fairly frequently, and can leave minor to major deformity. Injuries include: laceration, avulsion injuries, burn and repeated twisting or pulling of an ear, for discipline or torture. Chronic damage to the ears can cause cauliflower ear, a common condition in boxers and wrestlers in which the cartilage around the ears becomes lumpy and distorted owing to persistence of a haematoma around the perichondrium, which can impair blood supply and healing. Owing to its exposed position, the external ear is susceptible to frostbite as well as skin cancers, including squamous-cell carcinoma and basal-cell carcinomas.
The ear drum may become perforated in the event of a large sound or explosion, when diving or flying (called barotrauma), or by objects inserted into the ear. Another common cause of injury is due to an infection such as otitis media. These may cause a discharge from the ear called otorrhea, and are often investigated by otoscopy and audiometry. Treatment may include watchful waiting, antibiotics and possibly surgery, if the injury is prolonged or the position of the ossicles is affected. Skull fractures that go through the part of the skull containing the ear structures (the temporal bone) can also cause damage to the middle ear. A cholesteatoma is a cyst of squamous skin cells that may develop from birth or secondary to other causes such as chronic ear infections. It may impair hearing or cause dizziness or vertigo, and is usually investigated by otoscopy and may require a CT scan. The treatment for cholesteatoma is surgery.
There are two principal damage mechanisms to the inner ear in
industrialised society, and both injure hair cells. The first is
exposure to elevated sound levels (noise trauma), and the second is
exposure to drugs and other substances (ototoxicity). A large number
of people are exposed to sound levels on a daily basis that are likely
to lead to significant hearing loss. The National Institute for
Occupational Safety and Health has recently published research on the
estimated numbers of persons with hearing difficulty (11%) and the
percentage of those that can be attributed to occupational noise
exposure (24%). Furthermore, according to the National Health and
Nutrition Examination Survey (NHANES), approximately twenty-two
million (17%) US workers reported exposure to hazardous workplace
noise. Workers exposed to hazardous noise further exacerbate the
potential for developing noise-induced hearing loss when they do not
wear hearing protection.
Stretching of the earlobe and various cartilage piercings
The ears have been ornamented with jewelry for thousands of years,
traditionally by piercing of the earlobe. In ancient and modern
cultures, ornaments have been placed to stretch and enlarge the
earlobes, allowing for larger plugs to be slid into a large fleshy gap
in the lobe. Tearing of the earlobe from the weight of heavy earrings,
or from traumatic pull of an earring (for example, by snagging on a
sweater), is fairly common.
Injury to the ears has been present since Roman times as a method of
reprimand or punishment - "In Roman times, when a dispute arose that
could not be settled amicably, the injured party cited the name of the
person thought to be responsible before the Praetor; if the offender
did not appear within the specified time limit, the complainant
summoned witnesses to make statements. If they refused, as often
happened, the injured party was allowed to drag them by the ear and to
pinch them hard if they resisted. Hence the French expression "se
faire tirer l’oreille", of which the literal meaning is "to have
one's ear pulled" and the figurative meaning "to take a lot of
persuading". We use the expression "to tweak (or pull) someone's ears"
to mean "inflict a punishment"."
The pinnae have an effect on facial appearance. In Western societies,
protruding ears (present in about 5% of ethnic Europeans) have been
considered unattractive, particularly if asymmetric. The first
surgery to reduce the projection of prominent ears was published in
the medical literature by
Pinnae of the bat
The pinna helps direct sound through the ear canal to the eardrum. The complex geometry of ridges on the inner surface of some mammalian ears helps to sharply focus sounds produced by prey, using echolocation signals. These ridges can be regarded as the acoustic equivalent of a fresnel lens, and may be seen in a wide range of animals, including the bat, aye-aye, lesser galago, bat-eared fox, mouse lemur and others. Some large primates such as gorillas and orang-utans (and also humans) have undeveloped ear muscles that are non-functional vestigial structures, yet are still large enough to be easily identified. An ear muscle that cannot move the ear, for whatever reason, has lost that biological function. This serves as evidence of homology between related species. In humans, there is variability in these muscles, such that some people are able to move their ears in various directions, and it has been said that it may be possible for others to gain such movement by repeated trials. In such primates, the inability to move the ear is compensated for mainly by the ability to easily turn the head on a horizontal plane, an ability which is not common to most monkeys—a function once provided by one structure is now replaced by another. In some animals with mobile pinnae (like the horse), each pinna can be aimed independently to better receive the sound. For these animals, the pinnae help localise the direction of the sound source.
African bush elephant Loxodonta africana
Arctic fox Vulpes lagopus
Half-Lop Rabbit Illustration by Charles Darwin, 1868
The ear, with its blood vessels close to the surface, is an essential
thermoregulator in some land mammals, including the elephant, the fox,
and the rabbit. There are five types of ear carriage in domestic
rabbits, some of which have been bred for exaggerated ear
length—a potential health risk that is controlled in some
countries. Abnormalities in the skull of a half-lop rabbit were
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Anatomy: The Anatomical Basis of Clinical Practice (40 ed.).
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Archived from the original on 10 March 2014.
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^ Greinwald, John H. Jr MD; Hartnick, Christopher J. MD The Evaluation
of Children With Sensorineural
The dictionary definition of ear at Wiktionary Media related to Ears at Wikimedia Commons
v t e
Anatomy of hearing and balance
helix antihelix tragus antitragus intertragic notch earlobe
umbo pars flaccida
oval window round window secondary tympanic membrane prominence of facial canal promontory of tympanic cavity
mastoid cells aditus to mastoid antrum pyramidal eminence
superior ligament lateral ligament anterior ligament
superior ligament posterior ligament
stapedius tensor tympani
Auditory tube / Eustachian tube
Inner ear/ (membranous labyrinth, bony labyrinth)
Auditory system/ Cochlear labyrinth
Vestibular duct Helicotrema Tympanic duct Modiolus Cochlear cupula
Perilymph Cochlear aqueduct
Cochlear duct / scala media
Reissner's/vestibular membrane Basilar membrane Reticular membrane
Endolymph Stria vascularis Spiral ligament
Organ of Corti
stereocilia tip links
Tectorial membrane Sulcus spiralis
Claudius cell Boettcher cell
Vestibular system/ Vestibular labyrinth
Kinocilium Otolith Vestibular aqueduct
endolymphatic duct endolymphatic sac
Superior semicircular canal Posterior semicircular canal Horizontal semicircular canal
Ampullary cupula Ampullae
v t e
Cheek Chin Eye Mouth Nose Forehead
Jaw Occiput Scalp Temple
Adam's apple Throat
Waist Midriff Navel
Shoulder Axilla Brachium Elbow Forearm Wrist Hand Finger
Thumb Index Middle Ring Little
Buttocks Hip Thigh Knee Calf Foot
Ankle Heel Sole
General anatomy: systems and organs, regional anatomy, planes and lines, superficial axial anatomy, superficial anatomy of limbs