An ear is the

organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic keyboard instrument ** Hammond ...

that enables

hearing Hearing, or auditory perception, is the ability to perceive sounds In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psycholog ...

and, in mammals, body balance using the

vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...

. 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 (also pinna) and the ear canal. It gathers sound energy and focuses it on the eardrum (tympanic membrane). Structure Auricle The ...

, the

middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the ...

and the

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...

. 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 to the middle ear. The adult human ear canal extends from the pinna to the eardrum and is about in length and in diameter. Struc ...

. 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. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditory ...

and the three

ossicle The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ...

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, semicircular canals, and cochlea. These are cavities hollowed out of the s ...

, and contains structures which are key to several senses: the

semicircular canal In mathematics (and more specifically geometry), a semicircle is a one-dimensional locus of points that forms half of a circle. The full arc of a semicircle always measures 180° (equivalently, radians, or a half-turn). It has only one line of ...

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 verticall ...

, 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. A core component of the cochlea is the Organ of Corti, the sensory org ...

, which enables hearing. The ears of

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

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 direction and distance. The sound localization mechanisms of the mammalian auditory system have been extensively studied. The auditory system us ...

. The ear develops from the first pharyngeal pouch and six small swellings that develop in the early

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

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 auditory system, develops from the otic placode beginnin ...

s, which are derived from

ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from t ...

. 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 Hearing, hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to Language ...

tinnitus Tinnitus is the perception of sound when no corresponding external sound is present. Nearly everyone experiences a faint "normal tinnitus" in a completely quiet room; but it is of concern only if it is bothersome, interferes with normal hearin ...

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 ...

such as

vertigo Vertigo is a condition where a person has the sensation of movement 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 w ...

, 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 an ...

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

and

.Alt URL
/ref> The

of the outer ear is separated from the air-filled

of the middle ear by the

eardrum In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear The outer ear, external ear, or auris externa is the extern ...

. The middle ear contains the three small bones—the

ossicles The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ...

—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 vertebrae. It contains the pharynx and larynx. An important section of it is the epiglottis, separating the esophagus from the trachea (windpipe ...

at the

nasopharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...

, via the pharyngeal opening of the

Eustachian 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 d ...

. 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 structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The sa ...

organs—the utricle and

—and the

s belonging to the

, as well as the

of the

auditory system The auditory system is the sensory system for the sense of hearing. It includes both the sensory organs (the ears) and the auditory parts of the sensory system. System overview The outer ear funnels sound vibrations to the eardrum, increasin ...

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 () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, ...

, 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 on the pinna. The antihelix divides above into two ''legs'' or crura; the ''crura antiheli ...

, and opens into the

. 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 on the visible part of the ear, the pinna. The antitragus is located just above the earlobe and points anteriorly. It is separated from the tragus by the in ...

. 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 of length in the British imperial and the United States customary systems of measurement. It is equal to yard or of a foot. Derived from the Roman uncia ("twelfth") ...

(2.5 cm). The first part of the canal is surrounded by

cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...

, while the second part near the eardrum is surrounded by

bone A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...

. This bony part is known as the

auditory bulla The tympanic part of the temporal bone is a curved plate of bone lying below the squamous part of the temporal bone, in front of the mastoid process, and surrounding the external part of the ear canal. It originates as a separate bone (tympanic ...

and is formed by the

tympanic part of the temporal bone The tympanic part of the temporal bone is a curved plate of bone lying below the squamous part of the temporal bone, in front of the mastoid process, and surrounding the external part of the ear canal. It originates as a separate bone (tympanic ...

. The skin surrounding the ear canal contains

ceruminous Ceruminous 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 ou ...

and

sebaceous gland A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number ...

s that produce protective

ear wax An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists ...

. 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, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of tas ...

, 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 is a cutaneous nerve of the head. It originates from the cervical plexus, with branches of spinal nerves C2 and C3. It provides sensory nerve supply to the skin over the parotid gland and the mastoid process of the temp ...

, auricular nerve,

auriculotemporal nerve The auriculotemporal nerve is a branch of the mandibular nerve (CN 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 auriculotempo ...

, and

lesser Lesser, from Eliezer (, "Help/Court of my God"), is a surname. Notable people with the surname include: * Adolf Lesser (1851–1926), German physician * Aleksander Lesser (1814–1884), Polish painter and art critic * Anton Lesser (born 1952), Bri ...

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 p ...

s of the

cervical plexus The cervical plexus is a plexus of the anterior rami of the first four cervical spinal nerves which arise from C1 to C4 cervical segment in the neck. They are located laterally to the transverse processes between prevertebral muscles from the medi ...

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, fibroelastic cartilage or yellow fibrocartilage is a type of cartilage present in the pinnae (auricles) of the ear giving it shape, provides shape for the lateral region of the external auditory meatus, medial part of the audito ...

with a complicated relief on its inner surface and a fairly smooth configuration on its posterior surface. A

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection ...

, known as

Darwin's tubercle Darwin's tubercle (or auricular tubercle) is a congenital ear condition which often presents as a thickening on the helix at the junction of the upper and middle thirds. History This atavistic feature is so called because its description was f ...

, 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 areolar and adipose connective tissues, lacking the firmness and elasticity of the rest of the auricle (the external structure of the ear). In s ...

consists of

areola The human areola (''areola mammae'', or ) is the pigmented area on the breast around the nipple. Areola, more generally, is a small circular area on the body with a different histology from the surrounding tissue, or other small circular ar ...

and

adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular e ...

. 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 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 SO ...

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

and includes the three

and their attaching ligaments; the

auditory tube Auditory means of or relating to the process of hearing: * Auditory system, the neurological structures and pathways of sound perception ** Auditory bulla, part of auditory system found in mammals other than primates ** Auditory nerve, also known ...

; 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, circle, rounded rectangle, cant, or sphere * Rounding, the shortening of a number to reduce the number ...

and

oval window The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea of the inner ear. Vibrations that contact the tympanic membrane travel through the three ossicles and into the in ...

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 of the middle ear. It connects with the incus, and is attached to the inner surface of the eardrum. The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibrations fro ...

(hammer),

incus The ''incus'' (plural incudes) or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The ''incus'' receives vibrations from the ''malleus'', to which it is connected laterally, and transmit ...

(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, which allows the foot ...

(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 anima ...

. The middle ear also connects to the upper

at the

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

. The round window allows for the fluid within the inner ear to move. As the stapes pushes the

secondary tympanic membrane The round window is one of the two openings from the middle ear into the inner ear. It is sealed by the secondary tympanic membrane (round window membrane), which vibrates with opposite phase to vibrations entering the inner ear through the oval ...

, 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

. A central area known as the vestibule contains two small fluid-filled recesses, the utricle and saccule. These connect to the

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 in the inner ear and has the same general form; it is, howeve ...

. 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 of the inner ear. The major cation in endolymph is potassium, with the values of sodium and potassium concentration in the endolymph being 0.91 mM and 154 mM, respectively. I ...

, which fills the membranous labyrinth. The endolymph is situated in two vestibules, the utricle and

, 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 of the inner ear that conducts sound vibrations to the cochlear duct. It is separated from the cochlear duct by Reissner's membrane and extends from the vesti ...

, the

cochlear duct The cochlear duct (bounded by the scala media) is an endolymph filled cavity inside the cochlea, located between the tympanic duct and the vestibular duct, separated by the basilar membrane and the vestibular membrane (Reissner's membrane) resp ...

, and the

tympanic duct The tympanic duct or scala tympani is one of the perilymph-filled cavities in the inner ear of humans. It is separated from the cochlear duct by the basilar membrane, and it extends from the round window to the helicotrema, where it continues as ...

Hair cell Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment. ...

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. This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses' action potential. Transd ...

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 The posterior auricular artery is a small artery that arises from the external carotid artery, above the digastric muscle and stylohyoid muscle, opposite the apex of the styloid process. It ascends posteriorly beneath the parotid gland, along t ...

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 superficial temporal artery is a major artery of the head. It arises from the external carotid artery when it splits into the superficial temporal artery and maxillary artery. Its pulse can be felt above the zygomatic arch ...

. 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 occipital region. This artery supplies blood to the back of the scalp and sternocleidomastoid muscles ...

also plays a role. The middle ear is supplied by the mastoid branch of either the

occipital The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cereb ...

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 meatu ...

, a branch of the

maxillary artery The maxillary artery supplies deep structures of the face. It branches from the external carotid artery just deep to the neck of the mandible. Structure The maxillary artery, the larger of the two terminal branches of the external carotid artery ...

. Other arteries which are present but play a smaller role include branches of the

middle meningeal artery The middle meningeal artery ('' la, arteria meningea media'') is typically the third branch of the first portion of the maxillary artery. After branching off the maxillary artery in the infratemporal fossa, it runs through the foramen spinosum to ...

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 arch. It is the smallest branch of the external carotid and is a long, slender vessel, deeply sea ...

internal carotid artery The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these b ...

, and the artery of the

pterygoid canal The pterygoid canal (also vidian canal) is a passage in the sphenoid bone of the skull leading from just anterior to the foramen lacerum in the middle cranial fossa to the pterygopalatine fossa. Structure The pterygoid canal runs through the medi ...

. 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 that supplies blood to the cerebellum. It arises from the basilar artery on each side at the level of the junction between the medulla oblongata and the pons in the ...

or the

basilar artery The basilar artery () is one of the arteries that supplies the brain with oxygen-rich blood. The two vertebral arteries and the basilar artery are known as the vertebral basilar system, which supplies blood to the posterior part of the circle of W ...

Function

Hearing

Sound wave In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...

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 Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The 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

) 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 within the middle ear, located in the bony canal above the bony part of the auditory tube, and connects to the malleus bone. Its role is to dampen loud sounds, such as those produced from chewing, shouting, or thunde ...

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 or strirrup bone of the middle ear. Structure The stapedius emerges from ...

, also help modulate noise. The two muscles reflexively contract to dampen excessive vibrations. Vibration of the oval window causes vibration of the

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 The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a cranial nerve that transmits sound and equilibrium (balance) information from the inner ear to the bra ...

to the brain. The hollow channels of the inner ear are filled with liquid, and contain a sensory

epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

that is studded with

hair cells Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment. ...

. 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 that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...

s that release a chemical

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neuro ...

when stimulated. Sound waves moving through fluid flows against the

receptor Receptor may refer to: * Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...

cells of the

. The fluid pushes the filaments of individual cells; movement of the filaments causes receptor cells to become open to receive the

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

-rich endolymph. This causes the cell to depolarise, and creates an

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

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. These bipolar neurons innervate the hair cells of the organ of Corti. They project their axons to the ventral and dorsal co ...

, which sends information through the auditory portion of the

to the

of the brain. The human ear can generally hear sounds with frequencies between 20 Hz and 20

kHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...

( the audio range). 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 perce ...

(below 20 Hz) or

ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...

(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 consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

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 In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

, 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 on the apex of hair cells located in the sensory epithelium of the vertebrate inner ear. Anatomy in humans Kinocilia are found on the apical surface of hair cells and are involved in both the morphogenesis ...

. Within the gelatinous layer lie

s, tiny formations of 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 proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...

s within the cell membranes, creating

depolarisation In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is esse ...

and an

that is transmitted to the brain along the

. 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 (; ) 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, for holy water or ...

, 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 The vestibulo-ocular reflex (VOR) is a reflex acting to stabilize gaze during head movement, with eye movement due to activation of the vestibular system. The reflex acts to stabilize images on the retinas of the eye during head movement. Gaze ...

Development

During

embryogenesis An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

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. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals that are sister taxa to the sponges) produce two or three pr ...

: the

endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...

and

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every o ...

Inner ear

After implantation, around the second to third week the developing embryo consists of three layers:

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical E ...

and

. 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

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 auditory plate, over the region of the hind-brain The hindbrain ...

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, which will develop into the membranous labyrinth of the in ...

. This entire mass will eventually become surrounded by

to form the

. 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

. 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-filled cavity inside the cochlea of the inner ear that conducts sound vibrations to the cochlear duct. It is separated from the cochlear duct by Reissner's membrane and extends from the vesti ...

, the

scala tympani The tympanic duct or scala tympani is one of the perilymph-filled cavities in the inner ear of humans. It is separated from the cochlear duct by the basilar membrane, and it extends from the round window to the helicotrema, where it continues as v ...

and the

scala media Scala or SCALA may refer to: Automobiles * Renault Scala, multiple automobile models * Škoda Scala, a Czech compact hatchback Music * Scala (band), an English electronic music group * Escala (group), an electronic string quartet formerly known ...

. Both the scala vestibuli and the scala tympani contain an extracellular fluid called

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 that of plasma and cerebrospinal fluid. The major ca ...

. The scala media contains

. A set of membranes called the

vestibular membrane The vestibular membrane, vestibular wall or Reissner's membrane, is a diaphragm (acoustics), membrane inside the cochlea of the inner ear. It separates the cochlear duct from the vestibular duct. It helps to transmit vibrations from fluid in the ...

and the

basilar membrane The basilar membrane is a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani. The basilar membrane moves up and down in ...

develop to separate the cochlear duct from the vestibular duct and the tympanic duct, respectively. Parts of the otic vesicle in turn form the

. These form

bipolar neuron A bipolar neuron, or bipolar cell, is a type of neuron that has two extensions (one axon and one dendrite). Many bipolar cells are specialized sensory neurons for the transmission of sense. As such, they are part of the sensory pathways for smell ...

s 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 Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology and society, but the term has slightly different meanings according to context. For ...

of inner ear formation and its

morphogenesis Morphogenesis (from the Greek ''morphê'' shape and ''genesis'' creation, literally "the generation of form") is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of devel ...

are members of the

homeobox gene A homeobox is a DNA sequence, around 180 base pairs long, that regulates large-scale anatomical features in the early stages of embryonic development. For instance, mutations in a homeobox may change large-scale anatomical features of the full-g ...

family such as

Pax Pax or PAX may refer to: Peace * Peace (Latin: ''pax'') ** Pax (goddess), the Roman goddess of peace ** Pax, a truce term * Pax (liturgy), a salutation in Catholic and Lutheran religious services * Pax (liturgical object), an object formerly kiss ...

, Msx and Otx homeobox genes. The development of inner ear structures such as the

is regulated by

Dlx5 Homeobox protein DLX-5 is a protein that in humans is encoded by the distal-less homeobox 5 gene, or ''DLX5'' gene. DLX5 is a member of DLX gene family. Function This gene encodes a member of a homeobox transcription factor gene family simil ...

Dlx6 Homeobox protein DLX-6 is a protein that in humans is encoded by the ''DLX6'' gene. This gene encodes a member of a homeobox transcription factor gene family similar to the Drosophila ''Drosophila'' () is a genus of flies, belonging to the f ...

Otx1 Homeobox protein OTX1 is a protein that in humans is encoded by the ''OTX1'' gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''bi ...

Otx2 Homeobox protein OTX2 is a protein that in humans is encoded by the ''OTX2'' gene. Function This gene encodes a member of the bicoid sub-family of homeodomain-containing transcription factors. The encoded protein acts as a transcription factor ...

and

Pax2 Paired box gene 2, also known as Pax-2, is a protein which in humans is encoded by the ''PAX2'' gene. Function The Pax Genes, or Paired-Box Containing Genes, play important roles in the development and proliferation of multiple cell lines, dev ...

, which in turn are controlled by the master gene Shh. Shh is secreted by the

notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis ...

Middle ear

The middle ear and its components develop from the first and second

pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arch ...

es. 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 The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...

. 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 Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, per ...

. Eventually cells from the tissue surrounding the ossicles will experience

apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...

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 The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

. As the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

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 A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can r ...

, or

physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

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 Conductive hearing loss (CHL) occurs when there is a problem transferring sound waves anywhere along the pathway through the outer ear, tympanic membrane (eardrum), or middle ear ( ossicles). If a conductive hearing loss occurs in conjunction wi ...

. When deafness is a result of injury or damage to the inner ear, vestibulochoclear nerve, or brain, it is known as

sensorineural hearing loss Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII). SNHL accounts for about 90% of rep ...

. 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 Otitis media is a group of inflammatory diseases of the middle ear. One of the two main types is acute otitis media (AOM), an infection of rapid onset that usually presents with ear pain. In young children this may result in pulling at the ear, ...

Tympanoplasty Tympanoplasty is the surgical operation performed to reconstruct hearing mechanism of middle ear Classification Tympanoplasty is classified into five different types, originally described by Horst Ludwig Wullstein (1906–1987) in 1956. # Type 1 ...

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 aid A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers su ...

s or

cochlear implant A cochlear implant (CI) is a surgically implanted neuroprosthesis that provides a person who has moderate-to-profound sensorineural hearing loss with sound perception. With the help of therapy, cochlear implants may allow for improved speech und ...

s 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. Active middle ear implants send sound vibrations to the ossicles in the middle ear, bypassing any non-functioning parts of the outer and middle ear.

Congenital abnormalities

Anomalies and malformations of the pinna are common. These anomalies include chromosome syndromes such as

ring 18 Ring chromosome 18 is a genetic condition caused by a deletion of the two ends of chromosome 18 followed by the formation of a ring-shaped chromosome. It was first reported in 1964. Signs and symptoms Ring 18 causes a wide range of medical and ...

. Children may also present cases of abnormal ear canals and low ear implantation. In rare cases no pinna is formed (

atresia Atresia is a condition in which an orifice or passage in the body is (usually abnormally) closed or absent. Examples of atresia include: *Aural atresia, a congenital deformity where the ear canal is underdeveloped. * Biliary atresia, a condition i ...

), or is extremely small (

microtia Microtia is a congenital deformity where the auricle (external ear) is underdeveloped. A completely undeveloped pinna is referred to as anotia. Because microtia and anotia have the same origin, it can be referred to as microtia-anotia. 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 Otoplasty ( el, οὖς, , "ear" + , , "to shape") denotes the surgical and non-surgical procedures for correcting the deformities and defects of the pinna (external ear), and for reconstructing a defective, or deformed, or absent external ear, co ...

. 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 A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...

(CT) scan or a

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...

(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 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 stape ...

. 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

. One common type of vertigo is

benign paroxysmal positional vertigo Benign paroxysmal positional vertigo (BPPV) is a disorder arising from a problem in the inner ear. Symptoms are repeated, brief periods of vertigo with movement, characterized by a spinning sensation upon changes in the position of the head. * T ...

, when an

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 Ménière's disease (MD) is a disease of the inner ear that is characterized by potentially severe and incapacitating episodes of vertigo, tinnitus, hearing loss, and a feeling of fullness in the ear. Typically, only one ear is affected initial ...

labyrinthitis Labyrinthitis is inflammation of the labyrinth – a maze of fluid-filled channels in the inner ear. Vestibular neuritis is inflammation of the vestibular nerve – the nerve in the inner ear that sends messages related to motion and position t ...

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

s, 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 A wound is a rapid onset of injury that involves lacerated or punctured skin (an ''open'' wound), or a contusion (a ''closed'' wound) from blunt force trauma or compression. In pathology, a ''wound'' is an acute injury that damages the epiderm ...

avulsion injuries In medicine, an avulsion is an injury in which a body structure is torn off by either trauma or surgery (from the Latin ''avellere'', meaning "to tear off"). The term most commonly refers to a surface trauma where all layers of the skin have been ...

burn A burn is an injury to skin, or other tissues, caused by heat, cold, electricity, chemicals, friction, or ultraviolet radiation (like sunburn). Most burns are due to heat from hot liquids (called scalding), solids, or fire. Burns occur mainl ...

and repeated twisting or pulling of an ear, for discipline or torture. Chronic damage to the ears can cause

cauliflower ear Cauliflower ear is an irreversible condition that occurs when the external portion of the ear is hit and develops a blood clot or other collection of fluid under the perichondrium. This separates the cartilage from the overlying perichondrium tha ...

, a common condition in boxers and

wrestlers Wrestling is a series of combat sports involving grappling-type techniques such as clinch fighting, throws and takedowns, joint locks, pins and other grappling holds. Wrestling techniques have been incorporated into martial arts, combat spor ...

in which the cartilage around the ears becomes lumpy and distorted owing to persistence of a

haematoma A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is b ...

around the

perichondrium The perichondrium (from Greek el, περί, peri, around, label=none and el, χόνδρος, chondros, cartilage, label=none) is a layer of dense irregular connective tissue that surrounds the cartilage of developing bone. It consists of two sep ...

, which can impair blood supply and healing. Owing to its exposed position, the external ear is susceptible to

frostbite Frostbite is a skin injury that occurs when exposed to extreme low temperatures, causing the freezing of the skin or other tissues, commonly affecting the fingers, toes, nose, ears, cheeks and chin areas. Most often, frostbite occurs in the han ...

as well as

skin cancer Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. There are three main types of skin cancers: basal-cell skin cancer (BCC) ...

s, including

squamous-cell carcinoma Squamous-cell carcinomas (SCCs), also known as epidermoid carcinomas, comprise a number of different types of cancer that begin in squamous cells. These cells form on the surface of the skin, on the lining of hollow organs in the body, and on the ...

and

basal-cell carcinoma Basal-cell carcinoma (BCC), also known as basal-cell cancer, is the most common type of skin cancer. It often appears as a painless raised area of skin, which may be shiny with small blood vessels running over it. It may also present as a raise ...

s. ;Middle ear The ear drum may become perforated in the event of a large sound or explosion, when diving or flying (called

barotrauma Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in tensio ...

), 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 Otitis media is a group of inflammatory diseases of the middle ear. One of the two main types is acute otitis media (AOM), an infection of rapid onset that usually presents with ear pain. In young children this may result in pulling at the ear, ...

, and are often investigated by

otoscopy An otoscope or auriscope is a medical device which is used to look into the ears. Health care providers use otoscopes to screen for illness during regular check-ups and also to investigate ear symptoms. An otoscope potentially gives a view of ...

and

audiometry Audiometry () is a branch of audiology and the science of measuring hearing acuity for variations in sound intensity and pitch and for tonal purity, involving thresholds and differing frequencies. Typically, audiometric tests determine a subje ...

. Treatment may include

watchful waiting Watchful waiting (also watch and wait or WAW) is an approach to a medical problem in which time is allowed to pass before medical intervention or therapy is used. During this time, repeated testing may be performed. Related terms include ''expec ...

, 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 Cholesteatoma is a destructive and expanding growth consisting of keratinizing squamous epithelium in the middle ear and/or mastoid process. Cholesteatomas are not cancerous as the name may suggest, but can cause significant problems because of the ...

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 Ototoxicity is the property of being toxic to the ear (''oto-''), specifically the cochlea or auditory nerve and sometimes the vestibular system, for example, as a side effect of a drug. The effects of ototoxicity can be reversible and temporary, ...

). A large number of people are exposed to sound levels on a daily basis that are likely to lead to significant

. The

National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the C ...

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 The National Health and Nutrition Examination Survey (NHANES) is a survey research program conducted by the National Center for Health Statistics (NCHS) to assess the health and nutritional status of adults and children in the United States, and to ...

(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 Noise-induced hearing loss (NIHL) is a Hearing loss, hearing impairment resulting from exposure to loud sound. People may have a loss of perception of a narrow range of Frequency, frequencies or impaired perception of sound including hyperacusi ...

when they do not wear

hearing protection A hearing protection device, also known as a HPD, is an ear protection device worn in or over the ears while exposed to hazardous noise and provide hearing protection to help prevent noise-induced hearing loss. HPDs reduce the level of the no ...

Tinnitus

Tinnitus Tinnitus is the perception of sound when no corresponding external sound is present. Nearly everyone experiences a faint "normal tinnitus" in a completely quiet room; but it is of concern only if it is bothersome, interferes with normal hearin ...

is the hearing of

sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...

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 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

. Other causes include:

ear infection Otitis is a general term for inflammation or infection, inner ear infection, middle ear infection of the ear, in both humans and other animals. When infection is present, it may be viral or bacterial. When inflammation is present due to fluid buil ...

s, disease of the heart or blood vessels,

brain tumor A brain tumor occurs when abnormal cells form within the brain. There are two main types of tumors: malignant tumors and benign (non-cancerous) tumors. These can be further classified as primary tumors, which start within the brain, and seconda ...

emotional stress In psychology, stress is a feeling of emotional strain and pressure. Stress is a type of psychological pain. Small amounts of stress may be beneficial, as it can improve athletic performance, motivation and reaction to the environment. Excess ...

, exposure to certain medications, a previous

head injury A head injury is any injury that results in trauma to the skull or brain. The terms ''traumatic brain injury'' and ''head injury'' are often used interchangeably in the medical literature. Because head injuries cover such a broad scope of inju ...

, and

earwax 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 ...

. 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

piercing Body piercing, which is a form of body modification, is the practice of puncturing or cutting a part of the human body, creating an opening in which jewelry may be worn, or where an implant could be inserted. The word ''piercing'' can refer to ...

of the

. 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

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

Europeans Europeans are the focus of European ethnology, the field of anthropology related to the various ethnic groups that reside in the states of Europe. Groups may be defined by common genetic ancestry, common language, or both. Pan and Pfeil (2004) ...

) 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 Johann Karl Ernst Dieffenbach (27 January 1811 – 1 October 1855), also known as Ernest Dieffenbach, was a German physician, geologist and naturalist, the first trained scientist to live and work in New Zealand, where he travelled widely under t ...

in 1845, and the first

case report In medicine, a case report is a detailed report of the symptoms, signs, diagnosis, treatment, and follow-up of an individual patient. Case reports may contain a demographic profile of the patient, but usually describe an unusual or novel occurrence ...

in 1881.

Pointy ears Pointy ears or pointed ears are a characteristic of numerous animals, at least one genetic disorder in humans, as well as a cliché in popular culture, particularly in the fantasy genre. They are commonly known as elf ears. Animals "Pointy ears" ...

are a characteristic of some creatures in

folklore Folklore is shared by a particular group of people; it encompasses the traditions common to that culture, subculture or group. This includes oral traditions such as tales, legends, proverbs and jokes. They include material culture, ranging ...

such as the French

croquemitaine The Bogeyman (; also spelled boogeyman, bogyman, bogieman, boogie monster, boogieman, or boogie woogie) is a type of mythic creature used by adults to frighten children into good behavior. Bogeymen have no specific appearance and conceptions var ...

, Brazilian

curupira The ''Curupira'' () is a mythological creature of Brazilian folklore. The name comes from the Tupi language ''kuru'pir'', meaning "covered in blisters". According to the cultural legends, this creature has bright red/orange hair, and resemble ...

or Japanese

earth spider is a historical Japanese derogatory term for renegade local clans, and also the name for a race of spider-like yōkai in Japanese folklore. Alternative names for the mythological Tsuchigumo include and . In the '' Kojiki'' and in '' Nihon Shok ...

. It has been a feature of characters on art as old as that of

Ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...

and

medieval Europe In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...

. Pointy ears are a common characteristic of many creatures in the

fantasy Fantasy is a genre of speculative fiction involving Magic (supernatural), magical elements, typically set in a fictional universe and sometimes inspired by mythology and folklore. Its roots are in oral traditions, which then became fantasy ...

genre, including

elves An elf () is a type of humanoid supernatural being in Germanic mythology and folklore. Elves appear especially in North Germanic mythology. They are subsequently mentioned in Snorri Sturluson's Icelandic Prose Edda. He distinguishes "ligh ...

faeries A fairy (also fay, fae, fey, fair folk, or faerie) is a type of mythical being or legendary creature found in the folklore of multiple European cultures (including Celtic, Slavic, Germanic, English, and French folklore), a form of spirit, o ...

pixie A pixie (also pisky, pixy, pixi, pizkie, and piskie in Cornwall and Devon, and pigsie or puggsy in the New Forest) is a mythical creature of British folklore. Pixies are considered to be particularly concentrated in the high moorland areas arou ...

hobbit Hobbits are a fictional race of people in the novels of J. R. R. Tolkien. About half average human height, Tolkien presented hobbits as a variety of humanity, or close relatives thereof. Occasionally known as halflings in Tolkien's writings, ...

s, or

orcs An Orc (or Ork) is a fictional humanoid monster like a goblin. Orcs were brought into modern usage by the fantasy writings of J. R. R. Tolkien, especially ''The Lord of the Rings''. In Tolkien's works, Orcs are a brutish, aggressive, ugly, a ...

. They are a characteristic of creatures in the horror genre, such as

vampire A vampire is a mythical creature that subsists by feeding on the Vitalism, vital essence (generally in the form of blood) of the living. In European folklore, vampires are undead, undead creatures that often visited loved ones and caused mi ...

s. Pointy ears are also found in the

science fiction Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel unive ...

genre; for example among the

Vulcan Vulcan may refer to: Mythology * Vulcan (mythology), the god of fire, volcanoes, metalworking, and the forge in Roman mythology Arts, entertainment and media Film and television * Vulcan (''Star Trek''), name of a fictional race and their home p ...

and

Romulan The Romulans () are an extraterrestrial race in the American science fiction franchise ''Star Trek''. They first appeared in the series ''Star Trek'' (1966–1969). They have appeared in most subsequent ''Star Trek'' releases, including '' The A ...

races of the ''

Star Trek ''Star Trek'' is an American science fiction media franchise created by Gene Roddenberry, which began with the eponymous 1960s television series and quickly became a worldwide pop-culture phenomenon. The franchise has expanded into vari ...

'' universe and the Nightcrawler character from the

X-Men The X-Men are a superhero team appearing in American comic books published by Marvel Comics, first appearing in Uncanny X-Men, ''The X-Men'' #1 by artist/co-plotter Jack Kirby and writer/editor Stan Lee in 1963. Although initially cancelled in ...

universe.

Georg von Békésy Georg von Békésy ( hu, Békésy György, ; 3 June 1899 – 13 June 1972) was a Hungarian-American biophysicist. By using strobe photography and silver flakes as a marker, he was able to observe that the basilar membrane moves like a surface ...

was a Hungarian

biophysicist Biophysics is an interdisciplinary science that applies approaches and methods traditionally used in physics to study Biology, biological phenomena. Biophysics covers all scales of biological organization, from Molecule, molecular to organismic ...

born in

Budapest Budapest (, ; ) is the capital and most populous city of Hungary. It is the ninth-largest city in the European Union by population within city limits and the second-largest city on the Danube river; the city has an estimated population ...

Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croatia a ...

. In 1961, he was awarded the

Nobel Prize in Physiology or Medicine The Nobel Prize in Physiology or Medicine is awarded yearly by the Nobel Assembly at the Karolinska Institute for outstanding discoveries in physiology or medicine. The Nobel Prize is not a single prize, but five separate prizes that, accord ...

for his research on the function of the

in the mammalian hearing organ. The

Vacanti mouse The Vacanti mouse was a laboratory mouse (circa 1996) that had what looked like a human ear grown on its back. The "ear" was actually an ear-shaped cartilage structure grown by seeding cow cartilage cells into biodegradable ear-shaped mold and the ...

was a laboratory

mouse A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

that had what looked like a human ear grown on its back. The "ear" was actually an ear-shaped

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 A Fresnel lens ( ; ; or ) is a type of composite compact lens developed by the French physicist Augustin-Jean Fresnel (1788–1827) for use in lighthouses. It has been called "the invention that saved a million ships." The design allows the c ...

, and may be seen in a wide range of animals, including the

bat Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...

aye-aye The aye-aye (''Daubentonia madagascariensis'') is a long-fingered lemur, a strepsirrhine primate native to Madagascar with rodent-like teeth that perpetually grow and a special thin middle finger. It is the world's largest nocturnal primate. ...

lesser galago Lesser bushbabies, or lesser galagos, are strepsirrhine primates of the genus ''Galago''. They are classified, along with the bushbabies (genus ''Euoticus'') and the rest of the galagos (genera ''Otolemur'', ''Galagoides'', ''Paragalago'', and ''S ...

bat-eared fox The bat-eared fox (''Otocyon megalotis'') is a species of fox found on the African savanna. It is the only extant species of the genus ''Otocyon'' and considered a basal canid species. Fossil records indicate this canid first appeared during th ...

mouse lemur The mouse lemurs are nocturnal lemurs of the genus ''Microcebus''. Like all lemurs, mouse lemurs are native to Madagascar. Mouse lemurs have a combined head, body and tail length of less than , making them the smallest primates (the smallest spe ...

and others. Some large

primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...

s such as

gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...

s and

orang-utan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ' ...

s (and also

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

s) have undeveloped ear

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s that are non-functional

vestigial structure Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

s, yet are still large enough to be easily identified.

Darwin, Charles Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...

(1871). ''

The Descent of Man, and Selection in Relation to Sex ''The Descent of Man, and Selection in Relation to Sex'' is a book by English naturalist Charles Darwin, first published in 1871, which applies evolutionary theory to human evolution, and details his theory of sexual selection, a form of biolo ...

''. 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 Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor * Sequence homology, biological homology between DNA, RNA, or protein sequences *Homologous chrom ...

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 A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may ...

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. File:Elephant near ndutu.jpg, File:2009-03-07Vulpes zerda016.jpg, Image:Iceland-1979445.jpg, File:Rabbit - French Lop breed.jpg, Darwin Domestic 105

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 studied by Charles Darwin in 1868. In marine mammals,

earless seal The earless seals, phocids or true seals are one of the three main groups of mammals within the seal lineage, Pinnipedia. All true seals are members of the family Phocidae (). They are sometimes called crawling seals to distinguish them from th ...

s are one of three groups of

Pinnipedia Pinnipeds (pronounced ), commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae (whose only living member is the wal ...

Invertebrates

Only vertebrate animals have ears, though many invertebrates detect sound using other kinds of sense organs. In insects,

tympanal organ A tympanal organ (or tympanic organ) is a hearing organ in insects, consisting of a membrane ( tympanum) stretched across a frame backed by an air sac and associated sensory neurons. Sounds vibrate the membrane, and the vibrations are sensed by ...

s are used to hear distant sounds. They are located either on the head or elsewhere, depending on the insect

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

. The tympanal organs of some insects are extremely sensitive, offering acute hearing beyond that of most other animals. The female cricket fly ''

Ormia ochracea ''Ormia ochracea'' is a small yellow nocturnal fly in the family Tachinidae. It is notable for its parasitism of crickets and its exceptionally acute directional hearing. The female is attracted to the song of the male cricket and deposits larvae ...

'' 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

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s to detect 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 Oxford University Press (OUP) is the university press of the University of Oxford. It is the largest university press in the world, and its printing history dates back to the 1480s. Having been officially granted the legal right to print books ...

and allow them to respond to sound.

References

External links

* * {{Authority control Auditory system Human head and neck

Ear An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of ...

Structure

Outer ear

Middle ear

Inner ear

Blood supply

Function

Hearing

Balance

Development

Inner ear

Middle ear

Outer ear

Clinical significance

Hearing loss

Congenital abnormalities

Vertigo

Injury

Tinnitus

Society and culture

Other animals

Invertebrates

See also

References

External links