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The ear is the
organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly cate ...
that enables
hearing Schematic diagram of the human ear Hearing, or auditory perception, is the ability to perceive Sound, sounds through an organ, such as an ear, by detecting Vibration, vibrations as periodic changes in the pressure of a surrounding medium. Th ...

hearing
and, in mammals,
balance Balance may refer to: Common meanings * Balance (ability) in biomechanics * Balance (accounting) * Balance or weighing scale Arts and entertainment Film * Balance (1983 film), ''Balance'' (1983 film), a Bulgarian film * Balance (1989 film), ''Bal ...
. In mammals, the ear is usually described as having three parts—the
outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists of the auricle (anatomy), auricle (also pinna) and the ear canal. It gathers sound energy and focuses it on the eardrum (tympanic membrane). Stru ...
, the
middle ear The middle ear is the portion of the ear 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 The outer ear, external ear, or auris externa is th ...

middle ear
and the
inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated and led by the brothers and jazz musicians Tore Johansen and Roger Johansen (musician), Roger Johansen. They opened Inner Ear to release their music when their ...

inner ear
. The outer ear consists of the pinna and the
ear canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists of the auricle (anatomy), auricl ...
. 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 The tympanic cavity is a small cavity surrounding the bones of the middle ear The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the inner ear. The mammalian middle ear contains three ossicles, ...
and the three
ossicle The ossicles (also called auditory ossicles) are three bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of the body, produce red blood cel ...
s. The inner ear sits in the
bony labyrinth The bony labyrinth (also osseous labyrinth or otic capsule) is the rigid, bony outer wall of the inner ear in the temporal bone. It consists of three parts: the vestibule of the ear, vestibule, semicircular canals, and cochlea. These are cavities ho ...

bony labyrinth
, and contains structures which are key to several senses: the
semicircular canal The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals. Structure The sem ...
s, which enable balance and eye tracking when moving; the utricle and
saccule The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves vertically, ...
, which enable balance when stationary; and the
cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (cochlea), modiolus. A core component of the cochlea is the Organ of Cort ...

cochlea
, which enables hearing. The ears of
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
s are placed somewhat symmetrically on either side of the head, an arrangement that aids
sound localisation Sound localization is a listener's ability to identify the location or origin of a detected sound In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'natur ...
. The ear develops from the first pharyngeal pouch and six small swellings that develop in the early
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism that consists of more than one cell (biology), cell, in contrast to a unicellular organism. All species of animals, Embryophyte, la ...

embryo
called
otic placode In embryology, the otic placode is a thickening of the ectoderm on the outer surface of a developing embryo from which the ear develops. The ear, including both the vestibular system and the Cochlea, auditory system, develops from the otic placode b ...
s, which are derived from
ectoderm The ectoderm is one of the three primary germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrate Vertebrates () comprise all species of animal Animals (also ...

ectoderm
. The ear may be affected by disease, including infection and traumatic damage. Diseases of the ear may lead to
hearing loss Hearing loss is a partial or total inability to hear Hearing, or auditory perception, is the ability to perceive Sound, sounds by detecting Vibration, vibrations, changes in the pressure of the surrounding medium through time, through a ...
,
tinnitus Tinnitus is the perception of sound when no corresponding external sound is present. Nearly everyone will experience a faint "normal tinnitus" in a completely quiet room but it is only of concern if it is bothersome or interferes with normal h ...

tinnitus
and
balance disorders A balance disorder is a disturbance that causes an individual to feel unsteady, for example when standing or walking. It may be accompanied by feelings of giddiness, or wooziness, or having a sensation of movement, spinning, or floating. Balance B ...
such as
vertigo Vertigo is a condition where a person has the sensation of moving or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties wal ...

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
earring An earring is a piece of jewelry attached to the ear via a piercing in the earlobe or another external part of the ear (except in the case of clip earrings, which clip onto the lobe). Earrings have been worn by people in different civilizations ...

earring
s and other jewelry in numerous cultures for thousands of years, and has been subjected to surgical and cosmetic alterations.


Structure

The human ear consists of three parts—the
outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists of the auricle (anatomy), auricle (also pinna) and the ear canal. It gathers sound energy and focuses it on the eardrum (tympanic membrane). Stru ...
,
middle ear The middle ear is the portion of the ear 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 The outer ear, external ear, or auris externa is th ...

middle ear
and
inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated and led by the brothers and jazz musicians Tore Johansen and Roger Johansen (musician), Roger Johansen. They opened Inner Ear to release their music when their ...

inner ear
. The
ear canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists of the auricle (anatomy), auricl ...
of the outer ear is separated from the air-filled
tympanic cavity The tympanic cavity is a small cavity surrounding the bones of the middle ear The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the inner ear. The mammalian middle ear contains three ossicles, ...
of the middle ear by the
eardrum In the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is a ...
. The middle ear contains the three small bones—the
ossicles The ossicles (also called auditory ossicles) are three bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a spe ...
—involved in the transmission of sound, and is connected to the
throat In vertebrate anatomy, the throat is the front part of the neck, internally positioned in front of the vertebra, vertebrae. It contains the Human pharynx, pharynx and larynx. An important section of it is the epiglottis, separating the esophagus f ...

throat
at the
nasopharynx The pharynx (plural: pharynges) is the part of the throat In vertebrate anatomy, the throat is the front part of the neck, positioned in front of the vertebra. It contains the Human pharynx, pharynx and larynx. An important section of it is th ...
, via the pharyngeal opening of the
Eustachian tube In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Mole ...
. The inner ear contains the
otolith An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate Calcium carbonate is a chemical compound with the formula Ca CO3. It is a common substance found in rocks as th ...
organs—the utricle and
saccule The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves vertically, ...
—and the
semicircular canal The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals. Structure The sem ...
s belonging to the
vestibular system The vestibular system, in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, ...
, as well as the
cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (cochlea), modiolus. A core component of the cochlea is the Organ of Cort ...

cochlea
of the
auditory system The auditory system is the sensory system The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory receptor cells), neur ...
.


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 A helix (), plural helixes or helices (), is a shape like a corkscrew or spiral staircase. It is a type of smooth Smooth may refer to: Mathematics * Smooth function is a smooth function with compact support. In mathematical analysis, the ...
, the inner curved rim called the
antihelix The antihelix (anthelix) is a part of the visible ear; the pinna. The antihelix is a curved prominence of cartilage parallel with and in front of the helix Image:Helix.svg, The right-handed helix (cos ''t'', sin ''t'', ''t'') from ''t'' = 0 to 4 ...

antihelix
, and opens into the
ear canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists of the auricle (anatomy), auricl ...
. The tragus protrudes and partially obscures the ear canal, as does the facing
antitragus The antitragus is a feature of mammalian ear anatomy. In humans, it is a small Tubercle (anatomy)#Ears, tubercle on the visible part of the ear; the Pinna (anatomy), pinna. The antitragus is located just above the earlobe and points anatomical term ...

antitragus
. The hollow region in front of the ear canal is called the concha. The ear canal stretches for about 1
inch Measuring tape with inches The inch (symbol: in or ″) is a unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television s ...
(2.5 cm). The first part of the canal is surrounded by
cartilage Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue Elastic is a word often used to describe or identify certain types of elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-m ...

cartilage
, while the second part near the eardrum is surrounded by
bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubit ...

bone
. This bony part is known as the
auditory bulla The tympanic part of the temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temple (anat ...
and is formed by the
tympanic part of the temporal bone The tympanic part of the temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temple (anat ...
. The skin surrounding the ear canal contains
ceruminousCeruminous glands are specialized sudoriferous glands (sweat glands) located subcutaneously in the external auditory canal, in the outer 1/3. Ceruminous glands are simple, coiled, tubular glands made up of an inner secretory layer of cells and an out ...
and
sebaceous gland A sebaceous gland is a microscopic exocrine Exocrine glands are gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek participle , "setting in motion") is a ...
s that produce protective
ear wax Earwax, also known by the medical term cerumen, is a brown, orange, red, yellowish or gray waxy substance secreted in the ear canal of humans and other mammals. It protects the skin of the human ear canal, assists in cleaning and lubrication, a ...

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 In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass ...
and
extrinsic In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass ...
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 The facial nerve (the labyrinthine segment) is the seventh Cranial nerves, cranial nerve, or simply CN VII. It emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste sensation ...

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 The great auricular nerve originates from the cervical plexus, composed of branches of spinal nerves C2 and C3. It provides sensory innervation for the skin over parotid gland and mastoid process, and both surfaces of the outer ear. Pain resulting f ...
, auricular nerve,
auriculotemporal nerve The auriculotemporal nerve is a branch of the mandibular nerve (V3) that runs with the superficial temporal artery and vein, and provides sensory innervation to various regions on the side of the head. Structure Origin The auriculotemporal nerve ...
, and lesser and
greater occipital nerve The greater occipital nerve is a nerve of the head. It is a spinal nerve, specifically the medial branch of the dorsal primary ramus of cervical spinal nerve 2. It arises from between the first and second cervical vertebrae, ascends, and then pass ...
s of the
cervical plexus The cervical plexus is a plexus A plexus (from the Latin for "braid") is a branching network of vessels or nerves. The vessels may be blood vessels (veins, capillaries) or lymphatic vessels. The nerves are typically Axon, axons outside the centr ...

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 Elastic cartilage or yellow cartilage is a type of cartilage Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue, rubber-like padding that covers and protects the ends of long bone A bone is a Stiffness, rigid tissue (an ...
with a complicated relief on its inner surface and a fairly smooth configuration on its posterior surface. A
tubercle Image:Mammillaria marksiana.jpg, 250px, This view of the cactus ''Mammillaria marksiana'' shows its pattern of prominent tubercles, with the spines emanating from each tubercle's tip. In anatomy, a tubercle (literally 'small tuber', Latin for 'lum ...
, known as
Darwin's tubercle Darwin's tubercle (or auricular tubercle) is a congenital ear 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 The outer ear, external ear, or ...
, is sometimes present, lying in the descending part of the helix and corresponding to the ear-tip of mammals. The
earlobe The human earlobe (''lobulus auriculae''), the lower portion of the outer ear, is composed of tough Loose_connective_tissue#Areolar_tissue, areolar and adipose connective tissues, lacking the firmness and elasticity of the rest of the auricle (an ...
consists of
areola The human areola (''areola mammae'', Entry "areola"
in
adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biolo ...

adipose tissue
. The symmetrical arrangement of the two ears allows for the localisation of sound. The brain accomplishes this by comparing and intensities from each ear, in circuits located in the
superior olivary complex The superior olivary complex (SOC) or superior olive is a collection of brainstem nuclei that functions in multiple aspects of hearing and is an important component of the ascending and descending auditory pathways of the auditory system The aud ...
and the trapezoid bodies which are connected via pathways to both ears.


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 The tympanic cavity is a small cavity surrounding the bones of the middle ear The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the inner ear. The mammalian middle ear contains three ossicles, ...
and includes the three
ossicles The ossicles (also called auditory ossicles) are three bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a spe ...
and their attaching ligaments; the
auditory tube In anatomy, the Eustachian tube, also known as the auditory tube or pharyngotympanic tube, is a tube that links the nasopharynx to the middle ear, of which it is also a part. In adult humans, the Eustachian tube is approximately long and in di ...
; and the
round Round or rounds may refer to: Mathematics and science * The contour of a closed curve or surface with no sharp corners, such as an ellipse In , an ellipse is a surrounding two , such that for all points on the curve, the sum of the two ...
and
oval window The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, ...
s. 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 The malleus, or hammer, is a hammer-shaped small bone or ossicle The ossicles (also called auditory ossicles) are three bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. ...

malleus
(hammer),
incus The ''incus'' 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 transmits these to the ''s ...
(anvil), and the
stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its Annular ligament of stapes, annular ligam ...
(stirrup). The stapes is the smallest named bone in the
body Body may refer to: In science * Physical body, an object in physics that represents a large amount, has mass or takes up space * Body (biology), the physical material of an organism * Body plan, the physical features shared by a group of animals ...

body
. The middle ear also connects to the upper
throat In vertebrate anatomy, the throat is the front part of the neck, internally positioned in front of the vertebra, vertebrae. It contains the Human pharynx, pharynx and larynx. An important section of it is the epiglottis, separating the esophagus f ...

throat
at the
nasopharynx The pharynx (plural: pharynges) is the part of the throat In vertebrate anatomy, the throat is the front part of the neck, positioned in front of the vertebra. It contains the Human pharynx, pharynx and larynx. An important section of it is th ...
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 cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (cochlea), modiolus. A core component of the cochlea is the Organ of Cort ...

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 inner ear sits within the temporal bone in a complex cavity called the
bony labyrinth The bony labyrinth (also osseous labyrinth or otic capsule) is the rigid, bony outer wall of the inner ear in the temporal bone. It consists of three parts: the vestibule of the ear, vestibule, semicircular canals, and cochlea. These are cavities ho ...

bony labyrinth
. A central area known as the
vestibule Vestibule or Vestibulum can have the following meanings, each primarily based upon a common origin, from early 17th century French, derived from Latin ''vestibulum, -i n.'' "entrance court". Anatomy In general, vestibule is a small space or cavity ...
contains two small fluid-filled recesses, the utricle and saccule. These connect to the
semicircular canal The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals. Structure The sem ...
s 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 membranous labyrinth is a collection of fluid filled tubes and chambers which contain the receptors for the senses of equilibrium and hearing. It is lodged within the bony labyrinth The bony labyrinth (also osseous labyrinth or otic capsule) is ...
. 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 Endolymph is the fluid contained in the membranous labyrinth The membranous labyrinth is a collection of fluid filled tubes and chambers which contain the receptors for the senses of equilibrium and hearing. It is lodged within the bony labyrinth T ...
, which fills the membranous labyrinth. The endolymph is situated in two vestibules, the utricle and
saccule The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves vertically, ...
, and eventually transmits to the cochlea, a spiral-shaped structure. The cochlea consists of three fluid-filled spaces: the
vestibular duct The vestibular duct or scala vestibuli is a perilymph-filled cavity inside the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, ...
, the
cochlear duct The cochlear duct (bounded by the scala media) is an endolymph Endolymph is the fluid contained in the membranous labyrinth The membranous labyrinth is a collection of fluid filled tubes and chambers which contain the receptors for the senses o ...
, and the
tympanic duct The tympanic duct or scala tympani is one of the perilymph Perilymph is an extracellular fluid located within the inner ear. It is found within the scala tympani and scala vestibuli of the cochlea. The ionic composition of perilymph is comparable ...
.
Hair cell Hair cells are the sensory receptor Sensory neurons, also known as afferent neurons, are neuron A neuron or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cel ...
s responsible for transduction—changing mechanical changes into electrical stimuli are present in the
organ of Corti The organ of Corti, or spiral organ, is the receptor organ for hearing and is located in the mammalian cochlea The cochlea is the part of the inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated an ...

organ of Corti
in the cochlea.


Blood supply

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 Posterior may refer to: * Posterior (anatomy), the end of an organism opposite to its head ** Buttocks, as a euphemism * Posterior horn (disambiguation) * Posterior probability, the conditional probability that is assigned when the relevant evidence ...
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 In human anatomy 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 In biology Biology is the natur ...
. The
occipital artery The occipital artery arises from the external carotid artery opposite the facial artery. Its path is below the posterior belly of digastric to the occiput, occipital region. This artery supplies blood to the back of the scalp and sternocleidomastoi ...
also plays a role. The middle ear is supplied by the mastoid branch of either the
occipital The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occip ...
or posterior auricular arteries and the
deep auricular artery The deep auricular artery often arises in common with the anterior tympanic artery. It ascends in the substance of the parotid gland, behind the temporomandibular articulation, pierces the cartilaginous or bony wall of the external acoustic meatus, ...
, a branch of the
maxillary artery Maxillary means "related to the maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate s ...
. Other arteries which are present but play a smaller role include branches of the
middle meningeal artery Middle or The Middle may refer to: * Centre (geometry) In geometry, a centre (or center) (from Ancient Greek language, Greek ''κέντρον'') of an object is a point in some sense in the middle of the object. According to the specific definit ...

middle meningeal artery
,
ascending pharyngeal artery The ascending pharyngeal artery is an artery in the neck that supplies the pharynx, developing from the proximal part of the embryonic second Aortic arches, aortic arch. It is the smallest branch of the external carotid and is a long, slender vess ...
,
internal carotid artery The internal carotid artery (Latin: arteria carotis interna) is located in the inner side of the neck in contrast to the external carotid artery. In human anatomy, they arise from the common carotid arteries, where these bifurcate into the intern ...

internal carotid artery
, and the artery of the
pterygoid canal The pterygoid canal (also vidian canal) is a passage in the sphenoid bone of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the ...
. 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 The labyrinthine artery (auditory artery, internal auditory artery) is a branch of either the anterior inferior cerebellar artery or the basilar artery. It accompanies the vestibulocochlear nerve (CN VIII) through the internal acoustic meatus. It ...
, arising from either the
anterior inferior cerebellar artery The anterior inferior cerebellar artery (AICA) is one of three pairs of arteries An artery (plural arteries) () is a blood vessel that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries ...
or the
basilar artery The basilar artery () is one of the artery, arteries that supplies the human brain, brain with oxygen-rich blood. The two Vertebral artery, vertebral arteries and the basilar artery are sometimes together called the ''vertebrobasilar system'', whic ...
.


Function


Hearing

Sound wave In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...

Sound wave
s travel through the outer ear, are modulated by the middle ear, and are transmitted to the vestibulocochlear nerve in the inner ear. This nerve transmits information to the
temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex m ...

temporal lobe
of the brain, where it is registered as sound. Sound that travels through the outer ear impacts on the eardrum, and causes it to vibrate. The three ossicles bones transmit this sound to a second window (the
oval window The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, ...
) which protects the fluid-filled inner ear. In detail, the pinna of the outer ear helps to focus a sound, which impacts on the eardrum. The malleus rests on the membrane, and receives the vibration. This vibration is transmitted along the incus and stapes to the oval window. Two small muscles, the
tensor tympani The tensor tympani is a muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistr ...
and
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. Structure The stapedius emerges from a pinpoint foramen in the apex of th ...
, also help modulate noise. The two muscles reflexively contract to dampen excessive vibrations. Vibration of the oval window causes vibration of the
endolymph Endolymph is the fluid contained in the membranous labyrinth The membranous labyrinth is a collection of fluid filled tubes and chambers which contain the receptors for the senses of equilibrium and hearing. It is lodged within the bony labyrinth T ...
within the
vestibule Vestibule or Vestibulum can have the following meanings, each primarily based upon a common origin, from early 17th century French, derived from Latin ''vestibulum, -i n.'' "entrance court". Anatomy In general, vestibule is a small space or cavity ...
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 The vestibulocochlear nerve (auditory vestibular nerve), known as the eighth cranial nerve, transmits sound and equilibrium (balance) information from the inner ear to the brain. Through olivocochlear fibers, it also transmits motor and modulat ...

vestibulocochlear nerve
to the brain. The hollow channels of the inner ear are filled with liquid, and contain a sensory
epithelium Epithelium is one of the four basic types of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as ...
that is studded with
hair cells Hair cells are the sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an animal that coordinates its Be ...
. The microscopic "hairs" of these cells are structural protein filaments that project out into the fluid. The hair cells are
mechanoreceptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an ...
s that release a chemical
neurotransmitter A neurotransmitter is a signaling molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cells and coordinates multiple-cell actions. A signal is an entity that ...
when stimulated. Sound waves moving through fluid flows against the cells of the
organ of Corti The organ of Corti, or spiral organ, is the receptor organ for hearing and is located in the mammalian cochlea The cochlea is the part of the inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated an ...

organ of Corti
. The fluid pushes the filaments of individual cells; movement of the filaments causes receptor cells to become open to receive the
potassium Potassium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, b ...

potassium
-rich endolymph. This causes the cell to depolarise, and creates an
action potential In physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence ...

action potential
that is transmitted along the
spiral ganglion The spiral (cochlear) ganglion is a group of neuron cell bodies in the modiolus, the conical central axis of the cochlea The cochlea is the part of the inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label in ...
, which sends information through the auditory portion of the
vestibulocochlear nerve The vestibulocochlear nerve (auditory vestibular nerve), known as the eighth cranial nerve, transmits sound and equilibrium (balance) information from the inner ear to the brain. Through olivocochlear fibers, it also transmits motor and modulat ...

vestibulocochlear nerve
to the
temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex m ...

temporal lobe
of the brain. The human ear can generally hear sounds with frequencies between 20 and 20
kHz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatric ...
(). Sounds outside this range are considered
infrasound Infrasound, sometimes referred to as low status sound , describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz). Hearing becomes gradually less sensitive as frequency decreases, so for humans to per ...
(below 20 Hz) or
ultrasound Ultrasound is sound wave In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...

ultrasound
(above 20 kHz) Although hearing requires an intact and functioning auditory portion of the
central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
as well as a working ear, human deafness (extreme insensitivity to sound) most commonly occurs because of abnormalities of the inner ear, rather than in the nerves or tracts of the central auditory system.


Balance

Providing balance, when moving or stationary, is also a central function of the ear. The ear facilitates two types of balance: static balance, which allows a person to feel the effects of
gravity Gravity (), or gravitation, is a by which all things with or —including s, s, , and even —are attracted to (or ''gravitate'' toward) one another. , gravity gives to s, and the causes the s of the oceans. The gravitational attracti ...

gravity
, and dynamic balance, which allows a person to sense acceleration. Static balance is provided by two ventricles, the utricle and the saccule. Cells lining the walls of these ventricles contain fine filaments, and the cells are covered with a fine gelatinous layer. Each cell has 50–70 small filaments, and one large filament, the
kinocilium A kinocilium is a special type of cilium The cilium (; the plural is cilia) is an organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and li ...
. Within the gelatinous layer lie
otolith An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate Calcium carbonate is a chemical compound with the formula Ca CO3. It is a common substance found in rocks as th ...
s, tiny formations of
calcium carbonate Calcium carbonate is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held togethe ...

calcium carbonate
. When a person moves, these otoliths shift position. This shift alters the positions of the filaments, which opens
ion channel Ion channels are pore-forming membrane protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane ...

ion channel
s within the cell membranes, creating
depolarisation In biology, depolarization (British English: Depolarisation) is a change within a cell (biology), cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell. Depolarization is e ...
and an
action potential In physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence ...

action potential
that is transmitted to the brain along the
vestibulocochlear nerve The vestibulocochlear nerve (auditory vestibular nerve), known as the eighth cranial nerve, transmits sound and equilibrium (balance) information from the inner ear to the brain. Through olivocochlear fibers, it also transmits motor and modulat ...

vestibulocochlear nerve
. Dynamic balance is provided through the three semicircular canals. These three canals are orthogonal (at right angles) to each other. At the end of each canal is a slight enlargement, known as the
ampulla An ampulla (; plural ''ampullae'') was, in Ancient Rome, a small round vessel, usually made of glass and with two handles, used for sacred purposes. The word is used of these in archaeology, and of later flasks, often handle-less and much flatter, ...
, which contains numerous cells with filaments in a central area called the cupula. The fluid in these canals rotates according to the momentum of the head. When a person changes acceleration, the inertia of the fluid changes. This affects the pressure on the cupula, and results in the opening of ion channels. This causes depolarisation, which is passed as a signal to the brain along the vestibulocochlear nerve. Dynamic balance also helps maintain eye tracking when moving, via the vestibulo–ocular reflex.


Development

During
embryogenesis An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryogenesis
the ear develops as three distinct structures: the inner ear, the middle ear and the outer ear. Each structure originates from a different
germ layer A germ layer is a primary layer of cells that forms during embryonic development An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any ...
: the
ectoderm The ectoderm is one of the three primary germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrate Vertebrates () comprise all species of animal Animals (also ...

ectoderm
,
endoderm Endoderm is the innermost of the three primary germ layer A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazo ...
and
mesenchyme Mesenchyme () is a type of loosely organised animal embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, ...
.


Inner ear

After implantation, around the second to third week the consists of three layers:
endoderm Endoderm is the innermost of the three primary germ layer A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazo ...
,
mesoderm The mesoderm is the middle layer of the three germ layer A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoa ...

mesoderm
and
ectoderm The ectoderm is one of the three primary germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrate Vertebrates () comprise all species of animal Animals (also ...

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 placode In embryology, the otic placode is a thickening of the ectoderm on the outer surface of a developing embryo from which the ear develops. The ear, including both the vestibular system and the Cochlea, auditory system, develops from the otic placode b ...
s on either side of the head. Each otic placode recedes below the ectoderm, forms an
otic pit The auditory pit, also known as the otic pit, is the first rudiment of the internal ear. It appears shortly after that of the eye, in the form of a patch of thickened ectoderm, the Otic placode, auditory plate, over the region of the hind-brain. The ...
and then an
otic vesicle Otic vesicle, or auditory vesicle, consists of either of the two sac-like invaginations formed and subsequently closed off during embryonic development. It is part of the neural ectoderm The ectoderm is one of the three primary germ layers formed ...
. This entire mass will eventually become surrounded by
mesenchyme Mesenchyme () is a type of loosely organised animal embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, ...
to form the
bony labyrinth The bony labyrinth (also osseous labyrinth or otic capsule) is the rigid, bony outer wall of the inner ear in the temporal bone. It consists of three parts: the vestibule of the ear, vestibule, semicircular canals, and cochlea. These are cavities ho ...

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 The cochlear duct (bounded by the scala media) is an endolymph Endolymph is the fluid contained in the membranous labyrinth The membranous labyrinth is a collection of fluid filled tubes and chambers which contain the receptors for the senses o ...
. 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 vestibular duct or scala vestibuli is a perilymph Perilymph is an extracellular fluid located within the inner ear. It is found within the scala tympani and scala vestibuli of the cochlea. The ionic composition of perilymph is comparable to t ...
, the
scala tympani The tympanic duct or scala tympani is one of the perilymph-filled cavities in the inner ear of the human. It is separated from the cochlear duct by the basilar membrane, and it extends from the round window to the helicotrema, where it continu ...
and the scala media. Both the scala vestibuli and the scala tympani contain an extracellular fluid called perilymph. The scala media contains
endolymph Endolymph is the fluid contained in the membranous labyrinth The membranous labyrinth is a collection of fluid filled tubes and chambers which contain the receptors for the senses of equilibrium and hearing. It is lodged within the bony labyrinth T ...
. 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 The vestibulocochlear nerve (auditory vestibular nerve), known as the eighth cranial nerve, transmits sound and equilibrium (balance) information from the inner ear to the brain. Through olivocochlear fibers, it also transmits motor and modulat ...

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. ;Molecular regulation Most of the genes responsible for the Regulation of gene expression, regulation of inner ear formation and its morphogenesis are members of the homeobox gene family such as Pax genes, Pax, Msx and Otx homeobox genes. The development of inner ear structures such as the
cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (cochlea), modiolus. A core component of the cochlea is the Organ of Cort ...

cochlea
is regulated by DLX5 (gene), Dlx5/DLX6 (gene), Dlx6, OTX1 (gene), Otx1/OTX2 (gene), Otx2 and PAX2, Pax2, which in turn are controlled by the master SHH (gene), 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

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.


Clinical significance


Hearing loss

Hearing loss may be either partial or total. This may be a result of injury or damage, congenital disease, or physiology, physiological causes. When hearing loss is a result of injury or damage to the outer ear or middle ear, it is known as conductive hearing loss. When deafness is a result of injury or damage to the inner ear, vestibulochoclear nerve, or brain, it is known as sensorineural hearing loss. Causes of conductive hearing loss include an ear canal blocked by ear wax, ossicles that are fixed together or absent, or holes in the eardrum. Conductive hearing loss may also result from middle ear inflammation causing fluid build-up in the normally air-filled space, such as by otitis media. Tympanoplasty is the general name of the operation to repair the middle ear's eardrum and ossicles. Grafts from muscle fascia are ordinarily used to rebuild an intact eardrum. Sometimes artificial ear bones are placed to substitute for damaged ones, or a disrupted ossicular chain is rebuilt in order to conduct sound effectively. Hearing aids or cochlear implants may be used if the hearing loss is severe or prolonged. Hearing aids work by amplifying the sound of the local environment and are best suited to conductive hearing loss. Cochlear implants transmit the sound that is heard as if it were a nervous signal, bypassing the cochlea.


Congenital abnormalities

Anomalies and malformations of the pinna are common. These anomalies include chromosome syndromes such as ring 18. Children may also present cases of abnormal ear canals and low ear implantation. In rare cases no pinna is formed (Aural atresia, atresia), or is extremely small (microtia). Small pinnae can develop when the auricular hillocks do not develop properly. The ear canal can fail to develop if it does not channelise properly or if there is an obstruction. Reconstructive surgery to treat hearing loss is considered as an option for children older than five, with a cosmetic surgical procedure to reduce the size or change the shape of the ear is called an otoplasty. The initial medical intervention is aimed at assessing the baby's hearing and the condition of the ear canal, as well as the middle and inner ear. Depending on the results of tests, reconstruction of the outer ear is done in stages, with planning for any possible repairs of the rest of the ear. Approximately one out of one thousand children suffer some type of congenital deafness related to the development of the inner ear. Inner ear congenital anomalies are related to sensorineural hearing loss and are generally diagnosed with a computed tomography (CT) scan or a magnetic resonance imaging (MRI) scan. Hearing loss problems also derive from inner ear anomalies because its development is separate from that of the middle and external ear. Middle ear anomalies can occur because of errors during head and neck development. The first pharyngeal pouch syndrome associates middle ear anomalies to the malleus and incus structures as well as to the non-differentiation of the annular stapedial ligament. Temporal bone and ear canal anomalies are also related to this structure of the ear and are known to be associated with sensorineural hearing loss and conductive hearing loss.


Vertigo

Vertigo refers to the inappropriate perception of motion. This is due to dysfunction of the
vestibular system The vestibular system, in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, ...
. One common type of vertigo is benign paroxysmal positional vertigo, when an
otolith An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate Calcium carbonate is a chemical compound with the formula Ca CO3. It is a common substance found in rocks as th ...
is displaced from the ventricles to the semicircular canal. The displaced otolith rests on the cupola, causing a sensation of movement when there is none. Ménière's disease, labyrinthitis, strokes, and other infective and congenital diseases may also result in the perception of vertigo.


Injury

;Outer ear 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 boxing, boxers and wrestling, 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. ;Middle ear 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 Otoscope, 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. ;Inner ear 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 noise health effects, 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.


Tinnitus

Tinnitus is the hearing of sound when no external sound is present. While often described as a ringing, it may also sound like a clicking, hiss or roaring. Rarely, unclear voices or music are heard. The sound may be soft or loud, low Pitch (music), pitched or high pitched and appear to be coming from one ear or both. Most of the time, it comes on gradually. In some people, the sound causes depression, anxiety, or concentration difficulties. Tinnitus is not a disease but a symptom that can result from a number of underlying causes. One of the most common causes is noise-induced hearing loss. Other causes include: ear infections, cardiovascular disease, disease of the heart or blood vessels, Ménière's disease, brain tumors, Stress (psychological), emotional stress, exposure to certain medications, a previous head injury, and earwax. It is more common in those with depression and anxiety.


Society and culture

The ears have been ornamented with jewelry for thousands of years, traditionally by ear piercing, piercing of the
earlobe The human earlobe (''lobulus auriculae''), the lower portion of the outer ear, is composed of tough Loose_connective_tissue#Areolar_tissue, areolar and adipose connective tissues, lacking the firmness and elasticity of the rest of the auricle (an ...
. In ancient and modern cultures, ornaments have been placed to stretch and enlarge the earlobes, allowing for larger plug (jewellery), plugs to be slid into a large fleshy gap in the lobe. Tearing of the earlobe from the weight of heavy
earring An earring is a piece of jewelry attached to the ear via a piercing in the earlobe or another external part of the ear (except in the case of clip earrings, which clip onto the lobe). Earrings have been worn by people in different civilizations ...

earring
s, 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 European ethnic groups, 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 Ernst Dieffenbach in 1845, and the first case report in 1881. Pointy ears are a characteristic of some creatures in folklore such as the French croquemitaine, Brazilian curupira or Japanese earth spider. It has been a feature of characters on art as old as that of Ancient Greece and medieval Europe. Pointy ears are a common characteristic of many creatures in the fantasy genre, including elves, faeries, pixies, hobbits, or orcs. They are a characteristic of creatures in the horror literature, horror genre, such as vampires. Pointy ears are also found in the science fiction genre; for example among the Vulcan (Star Trek), Vulcan and Romulan races of the ''Star Trek'' universe and the Nightcrawler (comics), Nightcrawler character from the X-Men universe. Georg von Békésy was a Hungarian Biophysics, biophysicist born in Budapest, Hungary. In 1961, he was awarded the Nobel Prize in Physiology or Medicine for his research on the function of the
cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (cochlea), modiolus. A core component of the cochlea is the Organ of Cort ...

cochlea
in the mammalian hearing organ. The Vacanti mouse was a laboratory mouse that had what looked like a human ear grown on its back. The "ear" was actually an ear-shaped
cartilage Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue Elastic is a word often used to describe or identify certain types of elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-m ...

cartilage
structure grown by seeding cow cartilage cells into a biodegradable ear-shaped mold and then implanted under the skin of the mouse; then the cartilage naturally grew by itself. It was developed as an alternative to ear repair or grafting procedures and the results met with much publicity and controversy in 1997.


Other animals

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.Charles Darwin, Darwin, Charles (1871). ''The Descent of Man, and Selection in Relation to Sex''. John Murray: London. An ear muscle that cannot move the ear, for whatever reason, has lost that biological function. This serves as evidence of homology (biology), 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 sound localization, localise the direction of the sound source. File:Elephant near ndutu.jpg,
African bush elephant
''Loxodonta africana''
File:2009-03-07Vulpes zerda016.jpg,
Fennec fox (desert regions)
''Vulpes zerda''
Image:Iceland-1979445.jpg,
Arctic fox
''Vulpes lagopus''
File:Rabbit - French Lop breed.jpg,
Domestic rabbit – French Lop breed
''Oryctolagus cuniculus''
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 Lop rabbit#Ear type, 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 s:The Variation of Animals and Plants under Domestication, studied by Charles Darwin in 1868. In marine mammals, ''Earless seals'' are one of three groups of Pinnipedia.


Invertebrates

Only vertebrate animals have ears, though many invertebrates detect sound using other kinds of sense organs. In insects, tympanal organs are used to hear distant sounds. They are located either on the head or elsewhere, depending on the insect Family (biology), family. The tympanal organs of some insects are extremely sensitive, offering acute hearing beyond that of most other animals. The female cricket fly ''Ormia ochracea'' has tympanal organs on each side of her abdomen. They are connected by a thin bridge of exoskeleton and they function like a tiny pair of eardrums, but, because they are linked, they provide acute directional information. The fly uses her "ears" to detect the call of her host, a male cricket. Depending on where the song of the cricket is coming from, the fly's hearing organs will reverberate at slightly different frequencies. This difference may be as little as 50 billionths of a second, but it is enough to allow the fly to home in directly on a singing male cricket and parasitise it. Simpler structures allow other arthropods to detect wikt:near-field, near-field sounds. Spiders and cockroaches, for example, have hairs on their legs which are used for detecting sound. Caterpillars may also have hairs on their body that perceive vibrationsScoble, M.J. 1992. The Lepidoptera: Form, function, and diversity. Oxford University Press and allow them to respond to sound.


See also

* Hear, hear * Hearing test * Righting reflex


References


External links

* * {{Authority control Ear, Auditory system Human head and neck Sensory organs, Ear