For other uses see Ear (disambiguation). This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (June 2008) Ear Human (external) ear

The ear is the anatomical organ that detects sound. It not only acts as a receiver for sound but also plays a major role in the sense of balance and body position. The ear is part of the auditory system.

The word "ear" may be used correctly to describe the entire organ or just the visible portion. In most mammals the visible ear is a flap of tissue that is also called the pinna and is the first of many steps in hearing. In people the pinna is often called the auricle. Vertebrates have a pair of ears placed symmetrically on opposite sides of the head. This arrangement aids in the ability to localize sound sources. Contents 1 Introduction to ears and hearing 2 Mammalian ear 2.1 Outer ear (pinna ear canal surface of ear drum) 2.1.1 Human outer ear and culture 2.2 Middle ear 2.3 Inner ear: cochlea vestibule and semicircular canals 3 Damage to the human ear 3.1 Outer ear trauma 3.1.1 Auricle 3.1.2 Ear canal 3.2 Middle ear trauma 3.3 Inner ear trauma 4 Vestigial structures 5 Invertebrate hearing organs 6 See also 7 References 8 External links Introduction to ears and hearing

Audition is the scientific name for the sense of sound. Sound is a form of energy that moves through air water and other matter in waves of pressure. Sound is the means of auditory communication including frog calls bird songs and spoken language. Although the ear is the vertebrate sense organ that recognizes sound it is the brain and central nervous system that "hears". Sound waves are perceived by the brain through the firing of nerve cells in the auditory portion of the central nervous system. The ear changes sound pressure waves from the outside world into a signal of nerve impulses sent to the brain. Anatomy of the human ear. The length of the auditory canal is exaggerated for viewing purposes.

The outer part of the ear collects sound. That sound pressure is amplified through the middle portion of the ear and in land animals passed from the medium of air into a liquid medium. The change from air to liquid occurs because air surrounds the head and is contained in the ear canal and middle ear but not in the inner ear. The inner ear is hollow embedded in the temporal bone the densest bone of the body. The hollow channels of the inner ear are filled with liquid and contain a sensory epithelium that is studded with hair cells. The microscopic "hairs" of these cells are structural protein filaments that project out into the fluid. The hair cells are mechanoreceptors that release a chemical neurotransmitter when stimulated. Sound waves moving through fluid push the filaments; if the filaments bend over enough it causes the hair cells to fire. In this way sound waves are transformed into nerve impulses. In vision the rods and cones of the retina play a similar role with light as the hair cells do with sound. The nerve impulses travel from the left and right ears through the eighth cranial nerve to both sides of the brain stem and up to the portion of the cerebral cortex dedicated to sound. This auditory part of the cerebral cortex is in the temporal lobe.

The part of the ear that is dedicated to sensing balance and position also sends impulses through the eighth cranial nerve the VIIIth nerve's Vestibular Portion. Those impulses are sent to the vestibular portion of the central nervous system. The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz (the audio range). Although the sensation of hearing requires an intact and functioning auditory portion of the 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 the nerves or tracts of the central auditory system.1 Mammalian ear Bat pinnae come in different sizes and shapes

The shape of outer ear of mammals varies widely across species. However the inner workings of mammalian ears (including humans') are very similar. Outer ear (pinna ear canal surface of ear drum) Main article: Outer ear

The outer ear is the most external portion of the ear. The outer ear includes the pinna (also called auricle) the ear canal and the very most superficial layer of the ear drum (also called the tympanic membrane). In humans and almost all vertebrates the only visible portion of the ear is the outer ear. The word "ear" may properly refer to the pinna (the flesh covered cartilage appendage on either side of the head). This portion of the ear is very vital for hearing. The outer ear does help get sound (and imposes filtering) but the ear canal is very important. Unless the canal is open hearing will be dampened. Ear wax (cerumen) is produced by glands in the skin of the outer portion of the ear canal. This outer ear canal skin is applied to cartilage; the thinner skin of the deep canal lies on the bone of the skull. Only the thicker cerumen-producing ear canal skin has hairs. The outer ear ends at the most superficial layer of the tympanic membrane. The tympanic membrane is commonly called the ear drum. The pinna helps direct sound through the ear canal to the tympanic membrane (eardrum).

The framework of the auricle consists of a single piece of yellow fibrocartilage with a complicated relief on the anterior concave side and a fairly smooth configuration on the posterior convex side. The Darwinian tubercle which is present in some people lies in the descending part of the helix and corresponds to the true ear tip of the long-eared mammals. The lobule merely contains subcutaneous tissue.2 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 localize the direction of the sound source. Human beings localize sound within the central nervous system by comparing arrival-time differences and loudness from each ear in brain circuits that are connected to both ears. This process is commonly referred to as EPS or Echo Positioning System. Human outer ear and culture Stretching of the earlobe and various cartilage piercings

The auricles also have an effect on facial appearance. In Western societies protruding ears (present in about 5% of ethnic Europeans) have been considered unattractive particularly if asymmetric. The first surgery to reduce the projection of prominent ears was published in the medical literature in 1881. The ears have also been ornamented with jewelry for thousands of years traditionally by piercing of the earlobe. In some cultures ornaments are placed to stretch and enlarge the earlobes to make them very large. Tearing of the earlobe from the weight of heavy earrings or from traumatic pull of an earring (for example by snagging on a sweater being removed) is fairly common.3 The repair of such a tear is usually not difficult. A cosmetic surgical procedure to reduce the size or change the shape of the ear is called an otoplasty. In the rare cases when no pinna is formed (atresia) or is extremely small (microtia) reconstruction of the auricle is possible. Most often a cartilage graft from another part of the body (generally rib cartilage) is used to form the matrix of the ear and skin grafts or rotation flaps are used to provide the covering skin. Recently ears have been grown on a rat's back and attached to human heads after. However when babies are born without an auricle on one or both sides or when the auricle is very tiny the ear canal is ordinarily either small or absent and the middle ear often has deformities. 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.456 Middle ear Main article: Middle ear The middle ear an air-filled cavity behind the ear drum (tympanic membrane) includes the three ear bones or ossicles: the malleus (or hammer) incus (or anvil) and stapes (or stirrup). The opening of the Eustachian tube is also within the middle ear. The malleus has a long process (the manubrium or handle) that is attached to the mobile portion of the eardrum. The incus is the bridge between the malleus and stapes. The stapes is the smallest named bone in the human body. The three bones are arranged so that movement of the tympanic membrane causes movement of the malleus which causes movement of the incus which causes movement of the stapes. When the stapes footplate pushes on the oval window it causes movement of fluid within the cochlea (a portion of the inner ear). In humans and other land animals the middle ear (like the ear canal) is normally filled with air. Unlike the open ear canal however the air of the middle ear is not in direct contact with the atmosphere outside the body. The Eustachian tube connects from the chamber of the middle ear to the back of the nasopharynx. The middle ear is very much like a specialized paranasal sinus called the tympanic cavity; it like the paranasal sinuses is a hollow mucosa-lined cavity in the skull that is ventilated through the nose. The mastoid portion of the human temporal bone which can be felt as a bump in the skull behind the pinna also contains air which is ventilated through the middle ear. Middle Ear Malleus Tensor Tympani Incus Stapedius Labyrinth Stapes Auditory Canal Tympanic Membrane (Ear Drum) Eustachian Tube Tympanic cavity Components of the middle ear Normally the Eustachian tube is collapsed but it gapes open both with swallowing and with positive pressure. When taking off in an airplane the surrounding air pressure goes from higher (on the ground) to lower (in the sky). The air in the middle ear expands as the plane gains altitude and pushes its way into the back of the nose and mouth. On the way down the volume of air in the middle ear shrinks and a slight vacuum is produced. Active opening of the Eustachian tube is required to equalize the pressure between the middle ear and the surrounding atmosphere as the plane descends. The diver also experiences this change in pressure but with greater rates of pressure change; active opening of the Eustachian tube is required more frequently as the diver goes deeper into higher pressure. The arrangement of the tympanic membrane and ossicles works to efficiently couple the sound from the opening of the ear canal to the cochlea. There are several simple mechanisms that combine to increase the sound pressure. The first is the "hydraulic principle". The surface area of the tympanic membrane is many times that of the stapes footplate. Sound energy strikes the tympanic membrane and is concentrated to the smaller footplate. A second mechanism is the "lever principle". The dimensions of the articulating ear ossicles lead to an increase in the force applied to the stapes footplate compared with that applied to the malleus. A third mechanism channels the sound pressure to one end of the cochlea and protects the other end from being struck by sound waves. In humans this is called "round window protection" and will be more fully discussed in the next section. Abnormalities such as impacted ear wax (occlusion of the external ear canal) fixed or missing ossicles or holes in the tympanic membrane generally produce conductive hearing loss. Conductive hearing loss may also result from middle ear inflammation causing fluid build-up in the normally air-filled space. Tympanoplasty is the general name of the operation to repair the middle ear's tympanic membrane and ossicles. Grafts from muscle fascia are ordinarily used to rebuild an intact ear drum. Sometimes artificial ear bones are placed to substitute for damaged ones or a disrupted ossicular chain is rebuilt in order to conduct sound effectively. Inner ear: cochlea vestibule and semicircular canals Main article: Inner ear Inner Ear Posterior Canal Superior Canal Utricle Horizontal Canal Vestibule Cochlea Saccule Components of the inner ear The inner ear includes both the organ of hearing (the cochlea) and a sense organ that is attuned to the effects of both gravity and motion (labyrinth or vestibular apparatus). The balance portion of the inner ear consists of three semicircular canals and the vestibule. The inner ear is encased in the hardest bone of the body. Within this ivory hard bone there are fluid-filled hollows. Within the cochlea are three fluid filled spaces: the scala tympani the scala vestibuli and the scala media. The eighth cranial nerve comes from the brain stem to enter the inner ear. When sound strikes the ear drum the movement is transferred to the footplate of the stapes which presses it into one of its fluid-filled ducts through the oval window of cochlea . The fluid inside this duct is moved flowing against the receptor cells of the Organ of Corti which fire. These stimulate the spiral ganglion which sends information through the auditory portion of the eighth cranial nerve to the brain. Hair cells are also the receptor cells involved in balance although the hair cells of the auditory and vestibular systems of the ear are not identical. Vestibular hair cells are stimulated by movement of fluid in the semicircular canals and the utricle and saccule. Firing of vestibular hair cells stimulates the Vestibular portion of the eighth cranial nerve.7 Damage to the human ear Outer ear trauma Auricle The auricle can be easily damaged. Because it is skin-covered cartilage with only a thin padding of connective tissue rough handling of the ear can cause enough swelling to jeopardize the blood-supply to its framework the auricular cartilage. That entire cartilage framework is fed by a thin covering membrane called the perichondrium (meaning literally: around the cartilage). Any fluid from swelling or blood from injury that collects between the perichondrium and the underlying cartilage puts the cartilage in danger of being separated from its supply of nutrients. If portions of the cartilage starve and die the ear never heals back into its normal shape. Instead the cartilage becomes lumpy and distorted. Wrestler's Ear is one term used to describe the result because wrestling is one of the most common ways such an injury occurs. Cauliflower ear is another name for the same condition because the thickened auricle can resemble that vegetable. The lobule of the ear (ear lobe) is the one part of the human auricle that normally contains no cartilage. Instead it is a wedge of adipose tissue (fat) covered by skin. There are many normal variations to the shape of the ear lobe which may be small or large. Tears of the earlobe can be generally repaired with good results. Since there is no cartilage there is not the risk of deformity from a blood clot or pressure injury to the ear lobe. Other injuries to the external ear occur fairly frequently and can leave a major deformity. Some of the more common ones include laceration from glass knives and bite injuries avulsion injuries cancer frostbite and burns. Ear canal Ear canal injuries can come from firecrackers and other explosives and mechanical trauma from placement of foreign bodies into the ear. The ear canal is most often self-traumatized from efforts at ear cleaning. The outer part of the ear canal rests on the flesh of the head; the inner part rests in the opening of the bony skull (called the external auditory meatus). The skin is very different on each part. The outer skin is thick and contains glands as well as hair follicles. The glands make cerumen (also called ear wax). The skin of the outer part moves a bit if the pinna is pulled; it is only loosely applied to the underlying tissues. The skin of the bony canal on the other hand is not only among the most delicate skin in the human body it is tightly applied to the underlying bone. A slender object used to blindly clean cerumen out of the ear often results instead with the wax being pushed in and contact with the thin skin of the bony canal is likely to lead to laceration and bleeding. Middle ear trauma Like outer ear trauma middle ear trauma most often comes from blast injuries and insertion of foreign objects into the ear. 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. Small perforations of the tympanic membrane usually heal on their own but large perforations may require grafting. Displacement of the ossicles will cause a conductive hearing loss that can only be corrected with surgery. Forcible displacement of the stapes into the inner ear can cause a sensory neural hearing loss that cannot be corrected even if the ossicles are put back into proper position. Because human skin has a top waterproof layer of dead skin cells that are constantly shedding displacement of portions of the tympanic membrane or ear canal into the middle ear or deeper areas by trauma can be particularly traumatic. If the displaced skin lives within a closed area the shed surface builds up over months and years and forms a cholesteatoma. The -oma ending of that word indicates a tumour in medical terminology and although cholesteatoma is not a neoplasm (but a skin cyst) it can expand and erode the ear structures. The treatment for cholesteatoma is surgical. Inner ear trauma There are two principal damage mechanisms to the inner ear in industrialized 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). In 1972 the U.S. EPA told Congress that at least 34 million people were exposed to sound levels on a daily basis that are likely to lead to significant hearing loss.8 The worldwide implication for industrialized countries would place this exposed population in the hundreds of millions. 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 that can be attributed to occupational noise exposure (24%).9 Furthermore according to the National Health and Nutrition Examination Survey (NHANES) approximately twenty-two million (17%) US workers reported exposure to hazardous workplace noise.10 Workers exposed to hazardous noise further exacerbate the potential for developing noise induced hearing loss when they do not wear (hearing protection). Vestigial structures This section requires expansion. Comparative anatomy of primate ears: Human (left) and Barbary Macaque (right). Human ear (from Descent of Man) It has long been known that humans and indeed primates such as the orangutan and chimpanzee have ear muscles that are minimally developed and non-functional yet still large enough to be easily identifiable.11 These undeveloped muscles are vestigial structures. A muscle that cannot move the ear for whatever reason can no longer be said to have any biological function. This serves as evidence of homology between related species. In humans there is variability in these muscles such that some people are able to move their ears in various directions and it has been said that it may be possible for others to gain such movement by repeated trials.11 In such primates the inability to move the ear is compensated mainly by the ability to turn the head on a horizontal plane an ability which is not common to most monkeysa function once provided by one structure is now replaced by another.12 The outer structure of the ear also shows some vestigial features such as the node or point on the helix of the ear known as Darwin's tubercle which is found in around 10% of the population this feature is labelled (a) in the accompanying figure. Invertebrate hearing organs This section requires expansion. Only vertebrate animals have ears although many invertebrates are able to detect sound using other kinds of sense organs. In insects tympanal organs are used to hear distant sounds. They are not confined to the head but can occur in different locations depending on the group of insects.13 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 a 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 ear drums 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 parasitize it.14 Simpler structures allow arthropods 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 vibrations15 and allow them to respond to the sound. See also WikiSaurus:ear the WikiSaurus list of synonyms and slang words for ears in many languages Absolute threshold of hearing Acoustic reflex Auditory brainstem response (ABR) test Cerumen (ear wax) Cholesteatoma Ear pick Ear piercing Ear piercing instrument Earring Georg von Bksy winner of the 1961 Nobel Prize for his research on the cochlea Glossary of medical terms related to communications disorders Loudness Musical acoustics Noise health effects Otoplasty External Ear Surgery Pitch (music) Sound localization Timbre Tinnitus Vestibular system References Greinwald John H. Jr MD; Hartnick Christopher J. MD The Evaluation of Children With Hearing Loss. Archives of Otolaryngology Head & Neck Surgery. 128(1):84-87 January 2002 Stenstrm J. Sten: Deformities of the ear; In: Grabb W. C. Smith J.S. (Edited): Plastic Surgery Little Brown and Company Boston 1979 ISBN 0-316-32269-5 (C) ISBN 0-316-32268-7 (P) Deborah S. Sarnoff Robert H. Gotkin and Joan Swirsky (2002). Instant Beauty: Getting Gorgeous on Your Lunch Break. St. Martin's Press. ISBN 031228697X. http://books.google.com/booksidljeYTvylMC&pgPA60&otsptI8xjg9k&dqearlobe+tear+earring&sigYBnRJSoIUiA1KjhrzpqOdd0yk.  Lam SM. Edward Talbot Ely: father of aesthetic otoplasty. Biography. Historical Article. Journal Article Archives of Facial Plastic Surgery. 6(1):64 2004 Jan-Feb. Siegert R. Combined reconstruction of congenital auricular atresia and severe microtia. Evaluation Studies. Journal Article Laryngoscope. 113(11):2021-7; discussion 2028-9 2003 Nov. Trigg DJ. Applebaum EL. Indications for the surgical repair of unilateral aural atresia in children. Review 33 refs Journal Article. Review American Journal of Otology. 19(5):679-84; discussion 684-6 1998 September Anson and Donaldson Surgical Anatomy of the Temporal Bone 4th Edition Raven Press 1992 Senate Public Works Committee Noise Pollution and Abatement Act of 1972 S. Rep. No. 1160 92nd Cong. 2nd session. Tak SW Calvert GM "Hearing Difficulty Attributable to Employment by Industry and Occupation: An Analysis of the National Health Interview Survey - United States 1997 to 2003" J. Occup. Env. Med. 2008 50:46-56 Tak SW Davis RR Calvert GM "Exposure to Hazardous Workplace Noise and Use of Hearing Protection Devices Among US WOrkers 1999-2004" Am. J. Ind. Med. 2009 52:358-371 a b Darwin Charles (1871). The Descent of Man and Selection in Relation to Sex. John Murray: London. Mr. St. George Mivart Elementary Anatomy 1873 p. 396. Yack JE and JH Fullard 1993. What is an insect ear Ann. Entomol. Soc. Am. 86(6): 677-682. Piper Ross (2007) Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals Greenwood Press. Scoble MJ. 1992. The Lepidoptera: Form function and diversity. Oxford University Press. External links Look up ear in Wiktionary the free dictionary. Wikimedia Commons has media related to: Ear Protein behind hearing 3D Ear page Details of various ear problems Ear wiggling mechanism unmasked Cotton swabs can pose serious health risk: coroner from ctv.ca Radiology of the Ear Canal from MedPix v d eHuman systems and organs TA 24: MS Skeletal system Bone (Carpus  Collar bone (clavicle)  Thigh bone (femur)  Fibula  Humerus  Mandible  Metacarpus  Metatarsus  Ossicles  Patella  Phalanges  Radius  Skull (cranium)  Tarsus  Tibia  Ulna  Rib  Vertebra  Pelvis  Sternum)  Cartilage Joints Fibrous joint  Cartilaginous joint  Synovial joint Muscular system Muscle  Tendon  Diaphragm TA 511: splanchnic/ viscus mostly Thoracic Respiratory system URT (Nose Nasopharynx Larynx)  LRT (Trachea Bronchus Lung) mostly Abdominopelvic Digestive system+ adnexa Mouth (Salivary gland Tongue)  upper GI (Oropharynx Laryngopharynx Esophagus Stomach)  lower GI (Small intestine Appendix Colon Rectum Anus)  accessory (Liver Biliary tract Pancreas) GU: Urinary system Kidney  Ureter  Bladder  Urethra GU: Reproductive system Female (Uterus Vulva Ovary Placenta)  Male (Scrotum Penis Prostate Testicle Seminal vesicle) Endocrine system Pituitary  Pineal  Thyroid  Parathyroid  Adrenal  Islets of Langerhans TA 1216 Circulatory system Cardiovascular system peripheral (Artery Vein Lymphatic vessel)  Heart Lymphatic system primary (Bone marrow Thymus)  secondary (Spleen Lymph node) Nervous system (Brain Spinal cord Nerve)  Sensory system (Ear Eye) Integumentary system Skin  Subcutaneous tissue  Breast (Mammary gland) Blood (Non-TA) Myeloid Myeloid immune system Lymphoid Lymphoid immune system general anatomy: systems and organs regional anatomy planes and lines superficial axial anatomy superficial anatomy of limbs v d eSensory system: Auditory and Vestibular systems (TA A15.3 TH 3.11.09 GA 10.1029) Outer ear Pinna (Helix Antihelix Tragus Antitragus Incisura anterior auris Earlobe)  Ear canal  Auricular muscles Eardrum (Umbo Pars flaccida) Middle ear Tympanic cavity Labyrinthine wall/medial: Oval window  Round window  Secondary tympanic membrane  Prominence of facial canal  Promontory of tympanic cavity Membranous wall/lateral Mastoid wall/posterior: Mastoid cells  Aditus to mastoid antrum  Pyramidal eminence Carotid wall/anterior Tegmental wall/roof: Epitympanic recess Jugular wall/floor Ossicles Malleus (Neck of malleus Superior ligament of malleus Lateral ligament of malleus Anterior ligament of malleus)  Incus (Superior ligament of incus Posterior ligament of incus)  Stapes (Anular ligament of stapes) Muscles Stapedius  Tensor tympani Eustachian tube Bony part of pharyngotympanic tube  Cartilage of pharyngotympanic tube (Torus tubarius) Inner ear/ (membranous labyrinth bony labyrinth) Auditory system Cochlear labyrinth General cochlea Scala vestibuli  Helicotrema  Scala tympani  Modiolus  Cochlear cupula Perilymphatic space Perilymph  Cochlear aqueduct Cochlear duct / scala media Reissner's/vestibular membrane  Basilar membrane Endolymph  Stria vascularis  Spiral ligament Organ of Corti: Stereocilia  Tectorial membrane  Sulcus spiralis (externus internus)  Spiral limbus Cells Claudius cell  Boettcher cell Vestibular system/ Vestibular labyrinth Static/translations/vestibule/endolymphatic duct: Utricle (Macula)  Saccule (Macula Endolymphatic sac)  Kinocilium  Otolith  Vestibular aqueduct  Canalis reuniens Kinetic/rotations: Semicircular canals (Superior Posterior Horizontal)  Ampullary cupula  Ampullae (Crista ampullaris) M: EAR anat(e/p)/phys/devp noco/cong epon proc drug(S2) v d eHuman regional anatomy (TA A01.1) Head Forehead  Ear  Jaw  Face (Cheek Eye Nose Mouth Chin)  Occiput  Scalp  Temple Neck Throat  Adam's apple Trunk Chest (Breast)  Abdomen (Navel)  Back  Pelvis (Sex organs) Limbs Upper limb Shoulder  Axilla  Arm Elbow  Forearm Wrist  Hand  Finger (Thumb  Index  Middle  Ring  Little) Lower limb/ (see also leg) Hip  Buttocks  Thigh Knee  Calf  Crus Ankle  Heel  Foot  Toe (Hallux  Long   Third   Fourth   Fifth)  Sole general anatomy: systems and organs regional anatomy planes and lines superficial axial anatomy superficial anatomy of limbs