The outer ear is the external portion of the ear and includes the eardrum. The visible part is called the pinna, or auricle, and functions to collect and focus sound waves. Many mammals can move the pinna in order to focus their hearing in a certain direction in much the same way that they can turn their eyes. Humans have generally lost this ability. From the pinna the sound pressure waves move into the ear canal, a simple tube running to the middle ear. This tube amplifies frequencies in the range 3 kHz to 12 kHz.
The human ear has earlobes at the bottom, which are vestigial but are used by many people to provide an attachment point for earrings. The earlobe is usually formed cleft from the side of the face and hangs from the rest of the ear but occasionally will be found looking fused and "lobeless" due to a recessive gene. The helix is the outer edge of the outer ear.
The middle ear includes the ossicles (three tiny bones), two muscle tendons (of the stapedius and tensor tympani muscles), and two nerve bundles (the horizontal portion of the facial nerve and a branch of the facial nerve called the chorda tympani). The Latin names of the ossicles are the malleus, incus, and stapes, but they are also referred to by their English translations: the hammer, anvil, and stirrup respectively.
Mammals are unique in having three ear bones. The incus and stapes are derived from bones of the jaw, and allow finer detection of sound. These bones form the linkage between the tympanic membrane and the oval window that leads to the inner ear. The tympanum converts vibrations of air in the ear canal into vibrations of the ossicles. The ossicles in turn transmit the vibrations through the membrane of the oval window into the fluid of the inner ear. The ratio in area between the tympanic membrane and the oval window results in an effective amplification of approximately 14 dB, peaking at a frequency of around 1 kHz. The combined transfer function of the outer ear and middle ear gives humans a peak sensitivity to frequencies between 1 kHz and 3 kHz. The tensor tympani muscle and stapedius muscles of the middle ear contract in response to loud sounds, thereby reducing the transmission of sound to the inner ear. This is called the acoustic reflex.
The middle ear is hollow. If the animal moves to a high-altitude environment, or dives into the water, there will be a pressure difference between the middle ear and the outside environment. This pressure will pose a risk of bursting or otherwise damaging the tympanum if it is not relieved. This is one of the functions of the Eustachian tubes, evolutionary descendants of the gills, which connect the middle ear to the nasopharynx. The Eustachian tubes are normally pinched off at the nose end, to prevent being clogged with phlegm, but they may be opened by lowering and protruding the jaw; this is why yawning helps relieve the pressure felt in the ears when on board an aircraft.
The inner ear comprises both the organ of hearing (the cochlea) and the labyrinth or vestibular apparatus, the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule.
The cochlea (Latin for "snail") is a spiraled, hollow, conical chamber of bone filled with perilymph and endolymph (in the scala media), a fluid medium that receives the sound vibrations transmitted from the air to the oval window through the ear drum and ossicles of the middle ear (see above). Running through its centre is the cochlea duct, which contains the spiral Organ of Corti, the receptor organ responsible for hearing. The bony cavity of the cochlea is divided into three separate chambers: the scala vestibuli, which lies superior to the cochlea duct and abuts the oval window; the scala media, which is the membranous cochlea duct containing endolymph and the organ of Corti; and the scala tympani, which lies inferior to the scala media and terminates at the round window. The two bony chambers (scala vestibuli and scala tympani) both contain perilymph and join together at the cochlear apex, a region called the helicotrema. Separating the scala vestibuli from the scala media is the Reissner's membrane. The basilar membrane separates the scala media from the scala tympani. Sitting on top of the basilar membrane is a cellular layer known as the Organ of Corti, which is lined with hair cells — sensory cells topped with hair-like structures called stereocilia.
As the stapes oscillates against the oval window in response to sound, the perilymph within the scala vestibuli also oscillates. For very low frequencies (below 20Hz), the pressure waves propagate along the complete route of the cochlea - up scala vestibuli, around helicotrema and down scala tympani to the round window. Frequencies this low do not activate the organ of Corti and are below the threshold for hearing. Higher frequencies do not propagate to the helicotrema but are transmitted through the endolymph in the cochlea duct to the perilymph in the scala tympani. The hair cells in the organ of Corti are tuned to certain sound frequencies, being responsive to high frequencies near the oval window and to low frequencies near the apex of the cochlea.
All excited hair cells send nerve impulses to the brain, which are perceived as a sound of whatever pitch the hair cell is associated with. A very strong movement of the endolymph due to very loud noise may cause hair cells to die. This is a common cause of partial hearing loss and is the reason why anyone using firearms or heavy machinery should wear earmuffs or earplugs.
The vestibular apparatus is filled with the same endolymph as the cochlea, but instead of detecting sound, it detects rotation of the head. If a line is drawn through the middle of each of the three semicircular canals, perpendicular to the plane in which the canal lies, the three lines would be perpendicular. They would represent three axes of rotation. Any rotation could be represented as three simultaneous rotations about the three axes.
Problems with the ear or auditory processing system in the brain can lead to deafness. Other disorders related to auditory system are:
Benign Paroxysmal Positional Vertigo
Conductive hearing impairment
Noise-induced hearing loss
Nonsyndromic hereditary hearing impairment
Sensorineural hearing loss
Glossary of medical terms related to communications disorders such as blindness and deafness.
Acoustic neurinoma - tumor, usually benign, which may develop on the hearing and balance nerves and can cause gradual hearing loss, tinnitus, and/or dizziness. (sometimes called vestibular schwannoma). Also see Neurofibromatosis Type 2.
Acquired deafness - loss of hearing that occurs or develops some time during the lifespan but is not present at birth.
Ageusia - loss of the sense of taste.
Albinism - lack of normal pigment in the skin, eyes, and hair.
Alport syndrome - hereditary condition characterized by kidney disease, sensorineural hearing loss, and sometimes eye defects.
American Sign Language (ASL) - manual language with its own syntax and grammar, used primarily by people who are deaf.
Anosmia - absence of the sense of smell.
Aphasia - total or partial loss of the ability to use or understand language; usually caused by stroke, brain disease, or injury.
Aphonia - complete loss of voice.
Apraxia - inability to execute a voluntary movement despite being able to demonstrate normal muscle function.
Articulation disorder - inability to correctly produce speech sounds (phonemes) because of imprecise placement, timing, pressure, speed, or flow of movement of the lips, tongue, or throat.
Assistive devices - technical tools and devices such as alphabet boards, text telephones, or text-to-speech conversion software used to aid individuals who have communication disorders perform actions, tasks, and activities.
Audiologist - health care professional who is trained to evaluate hearing loss and related disorders, including balance (vestibular) disorders and tinnitus, and to rehabilitate individuals with hearing loss and related disorders. An audiologist uses a variety of tests and procedures to assess hearing and balance function and to fit and dispense hearing aids and other assistive devices for hearing.
Auditory Brainstem Response test (ABR test) - a test for brain functioning in comatose, unresponsive, etc., patients, and for hearing in infants and young children; involves attaching electrodes to the head to record electrical activity from the hearing nerve and other parts of the brain.
Auditory nerve - eighth cranial nerve that connects the inner ear to the brainstem and is responsible for hearing and balance.
Auditory perception - ability to identify, interpret, and attach meaning to sound.
Auditory prosthesis - device that substitutes or enhances the ability to hear.
Augmentative devices - tools that help individuals with limited or absent speech to communicate, such as communication boards, pictographs (symbols that look like the things they represent), or ideographs (symbols representing ideas).
Aural rehabilitation - techniques used with people who are hearing impaired to improve their ability to speak and communicate.
Autoimmune deafness - individual's immune system produces abnormal antibodies that react against the body's healthy tissues.
Autism - brain disorder that begins in early childhood and persists throughout adulthood; affects three crucial areas of development: communication, social interaction, and creative or imaginative play.
Balance - biological system that enables individuals to know where their bodies are in the environment and to maintain a desired position. Normal balance depends on information from the labyrinth in the inner ear, from other senses such as sight and touch, and from muscle movement.
Balance disorder - disruption in the labyrinth, the inner ear organ that controls the balance system, which allows individuals to know where their bodies are in the environment. The labyrinth works with other systems in the body, such as the visual and skeletal systems, to maintain posture.
Barotrauma - injury to the middle ear caused by a reduction of air pressure.
Benign Paroxysmal Positional Vertigo (BPPV) - balance disorder that results in sudden onset of dizziness, spinning, or vertigo when moving the head.
Brainstem implant - auditory prosthesis that bypasses the cochlea and auditory nerve. This type of implant helps individuals who cannot benefit from a cochlear implant because the auditory nerves are not working.
Captioning - text display of spoken words, presented on a television or a movie screen, that allows a deaf or hard-of-hearing viewer to follow the dialogue and the action of a program simultaneously.
Central auditory processing disorder - inability to differentiate, recognize, or understand sounds; hearing and intelligence are normal.
Chemosensory disorders - diseases or problems associated with the sense of smell or the sense of taste.
Cholesteatoma - accumulation of dead cells in the middle ear, caused by repeated middle ear infections.
Cochlea - snail-shaped structure in the inner ear that contains the organ of hearing.
Cochlear implant - medical device that bypasses damaged structures in the inner ear and directly stimulates the auditory nerve, allowing some deaf individuals to learn to hear and interpret sounds and speech.
Cognition - thinking skills that include perception, memory, awareness, reasoning, judgment, intellect, and imagination.
Conductive hearing impairment - hearing loss caused by dysfunction of the outer or middle ear.
Cued speech - method of communication that combines speech reading with a system of handshapes placed near the mouth to help deaf or hard-of-hearing individuals differentiate words that look similar on the lips (e.g., bunch vs. punch) or are hidden (e.g., gag).
Cytomegalovirus (Congenital) - one group of herpes viruses that infects humans and can cause a variety of clinical symptoms, including deafness or hearing impairment; infection with the virus may be either before or after birth.
Decibel - unit that measures the intensity or loudness of sound.
Dizziness - physical unsteadiness, imbalance, and lightheadedness associated with balance disorders.
Dysarthria - group of speech disorders caused by disturbances in the strength or coordination of the muscles of the speech mechanism as a result of damage to the brain or nerves.
Dysequilibrium - any disturbance of balance.
Dysfluency - disruption in the smooth flow or expression of speech.
Dysgeusia - distortion or absence of the sense of taste.
Dyslexia - learning disability characterized by reading difficulties. Some individuals may also have difficulty writing, spelling, or working with numbers.
Dysosmia - distortion or absence of the sense of smell.
Dysphagia - difficulty swallowing.
Dysphonia - any impairment of the voice or speaking ability.
Dyspraxia of speech - in individuals with normal muscle tone and speech muscle coordination, partial loss of the ability to consistently pronounce words.
Dystonia - abnormal muscle tone of one or more muscles.
Ear infection - presence and growth of bacteria or viruses in the ear.
Ear wax - yellow secretion from glands in the outer ear (cerumen) that keeps the skin of the ear dry and protected from infection.
Endolymph - fluid in the labyrinth (the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule).
Gustation - act or sensation of tasting.
Hair cells - sensory cells of the inner ear, which are topped with hair-like structures, the stereocilia, and which transform the mechanical energy of sound waves into nerve impulses.
Haptic sense - sense of physical contact or touch.
Haptometer - instrument for measuring sensitivity to touch.
Hearing - series of events in which sound waves in the air are converted to electrical signals, which are sent as nerve impulses to the brain, where they are interpreted.
Hearing aid - electronic device that brings amplified sound to the ear. A hearing aid usually consists of a microphone, amplifier, and receiver.
Hearing disorder - disruption in the normal hearing process that may occur in outer, middle, or inner ear, whereby sound waves are not conducted to the inner ear, converted to electrical signals and/or nerve impulses are not transmitted to the brain to be interpreted.
Hereditary hearing impairment - hearing loss passed down through generations of a family.
Hoarseness - abnormally rough or harsh-sounding voice caused by vocal abuse and other disorders such as gastroesophageal reflux, thyroid problems, or trauma to the larynx (voice box).
Hypogeusia - diminished sensitivity to taste.
Hyposmia - diminished sensitivity to smell.
Inner ear - part of the ear that contains both the organ of hearing (the cochlea) and the organ of balance (the labyrinth).
Kallmann's syndrome - disorder that can include several characteristics such as absence of the sense of smell and decreased functional activity of the gonads (organs that produce sex cells), affecting growth and sexual development.
Labyrinth - organ of balance located in the inner ear. The labyrinth consists of three semicircular canals and the vestibule.
Labyrinthine hydrops - excessive fluid in the organ of balance (labyrinth); can cause pressure or fullness in the ears, hearing loss, dizziness, and loss of balance.
Labyrinthitis - viral or bacterial infection or inflammation of the inner ear that can cause dizziness, loss of balance, and temporary hearing loss.
Landau-Kleffner syndrome - childhood disorder of unknown origin which often extends into adulthood and can be identified by gradual or sudden loss of the ability to understand and use spoken language.
Language - system for communicating ideas and feelings using sounds, gestures, signs, or marks.
Language disorders - any of a number of problems with verbal communication and the ability to use or understand a symbol system for communication.
Laryngeal neoplasms - abnormal growths in the larynx (voice box) that can be cancerous or noncancerous.
Laryngeal nodules - noncancerous, callous-like growths on the inner parts of the vocal folds (vocal cords); usually caused by vocal abuse or misuse.
Laryngeal paralysis - loss of function or feeling of one or both of the vocal folds caused by injury or disease to the nerves of the larynx.
Laryngectomy - surgery to remove part or all of the larynx (voice box).
Laryngitis - hoarse voice or the complete loss of the voice because of irritation to the vocal folds (vocal cords).
Larynx - valve structure between the trachea (windpipe) and the pharynx (the upper throat) that is the primary organ of voice production.
Learning disabilities - childhood disorders characterized by difficulty with certain skills such as reading or writing in individuals with normal intelligence.
Mastoid - back portion of the temporal bone that contains the inner ear.
Mastoid surgery - surgical procedure to remove infection from the mastoid bone.
Meige syndrome - movement disorder that can involve excessive eye blinking (blepharospasm) with involuntary movements of the jaw muscles, lips, and tongue (oromandibular dystonia).
Ménière's disease - inner ear disorder that can affect both hearing and balance. It can cause episodes of vertigo, hearing loss, tinnitus, and the sensation of fullness in the ear.
Meningitis - inflammation of the meninges, the membranes that envelop the brain and the spinal cord; may cause hearing loss or deafness.
Middle ear - part of the ear that includes the eardrum and three tiny bones of the middle ear, ending at the round window that leads to the inner ear.
Misarticulation - inaccurately produced speech sound (phoneme) or sounds.
Motion sickness - dizziness, sweating, nausea, vomiting, and generalized discomfort experienced when an individual is in motion.
Motor speech disorders - group of disorders caused by the inability to accurately produce speech sounds (phonemes) because of muscle weakness or incoordination or difficulty performing voluntary muscle movements.
Neural plasticity - ability of the brain and/or certain parts of the nervous system to adapt to new conditions, such as an injury.
Neural prostheses - devices that substitute for an injured or diseased part of the nervous system, such as the cochlear implant.
Neural stimulation - to activate or energize a nerve through an external source.
Neurofibromatosis Type 1 (NF-1 von Recklinghausen's) - group of inherited disorders in which noncancerous tumors grow on several nerves that may include the hearing nerve. The symptoms of NF-1 include coffee-colored spots on the skin, enlargement, deformation of bones, and neurofibromas.
Neurofibromatosis Type 2 (NF-2) - group of inherited disorders in which noncancerous tumors grow on several nerves that usually include the hearing nerve. The symptoms of NF-2 include tumors on the hearing nerve which can affect hearing and balance. NF-2 may occur in the teenage years with hearing loss. Also see acoustic neurinoma.
Neurogenic communication disorder - inability to exchange information with others because of hearing, speech, and/or language problems caused by impairment of the nervous system (brain or nerves).
Noise-induced hearing loss - hearing loss caused by exposure to harmful sounds, either very loud impulse sound(s) or repeated exposure to sounds over 90-decibel level over an extended period of time that damage the sensitive structures of the inner ear.
Nonsyndromic hereditary hearing impairment - hearing loss or deafness that is inherited and is not associated with other inherited clinical characteristics.
Odorant - substance that stimulates the sense of smell.
Olfaction - the act of smelling.
Olfactometer - device for estimating the intensity of the sense of smell.
Open-set speech recognition - understanding speech without visual clues (speech reading).
Otitis externa - inflammation of the outer part of the ear extending to the auditory canal.
Otitis media - inflammation of the middle ear caused by infection.
Otoacoustic emissions - low-intensity sounds produced by the inner ear that can be quickly measured with a sensitive microphone placed in the ear canal.
Otolaryngologist - physician/surgeon who specializes in diseases of the ears, nose, throat, and head and neck.
Otologist - physician/surgeon who specializes in diseases of the ear.
Otosclerosis - abnormal growth of bone of the inner ear. This bone prevents structures within the ear from working properly and causes hearing loss. For some people with otosclerosis, the hearing loss may become severe.
Ototoxic drugs - drugs such as a special class of antibiotics, aminoglycoside antibiotics, that can damage the hearing and balance organs located in the inner ear for some individuals.
Outer ear - external portion of the ear, consisting of the pinna, or auricle, and the ear canal.
Papillomavirus - group of viruses that can cause noncancerous wart-like tumors to grow on the surface of skin and internal organs such as the respiratory tract; can be life-threatening.
Parosmia - any disease or perversion of the sense of smell, especially the subjective perception of odors that do not exist.
Perception (Hearing) - process of knowing or being aware of information through the ear.
Perilymph fistula - leakage of inner ear fluid to the middle ear that occurs without apparent cause or that is associated with head trauma, physical exertion, or barotrauma.
Pervasive developmental disorders - disorders characterized by delays in several areas of development that may include socialization and communication.
Pheromones - chemical substances secreted by an animal that elicits a specific behavioral or physiological response in another animal of the same species.
Phonology - study of speech sounds.
Postlingually deafened - individual who becomes deaf after having acquired language.
Prelingually deafened - individual who is either born deaf or who lost his or her hearing early in childhood, before acquiring language.
Presbycusis - loss of hearing that gradually occurs because of changes in the inner or middle ear in individuals as they grow older.
Reading disorders - any of a group of problems characterized by difficulty using or understanding the symbol system for written language.
Round window - membrane separating the middle ear and inner ear.
Sensorineural hearing loss - hearing loss caused by damage to the sensory cells and/or nerve fibers of the inner ear.
Sign language - method of communication for people who are deaf or hard of hearing in which hand movements, gestures, and facial expressions convey grammatical structure and meaning.
Smell - to perceive odor or scent through stimuli affecting the olfactory nerves. See olfaction.
Smell disorder - inability to perceive odors. It may be temporary, caused by a head cold or swelling or blockage of the nasal passages. It can be permanent when any part of the olfactory region is damaged by factors such as brain injury, tumor, disease, or chronic rhinitis.
Sound vocalization - ability to produce voice.
Spasmodic dysphonia - momentary disruption of voice caused by involuntary movements of one or more muscles of the larynx or voice box.
Specific language impairment (SLI) - difficulty with language or the organized-symbol system used for communication in the absence of problems such as mental retardation, hearing loss, or emotional disorders.
Speech - spoken communication.
Speech disorder - any defect or abnormality that prevents an individual from communicating by means of spoken words. Speech disorders may develop from nerve injury to the brain, muscular paralysis, structural defects, hysteria, or mental retardation.
Speech processor - part of a cochlear implant that converts speech sounds into electrical impulses to stimulate the auditory nerve, allowing an individual to understand sound and speech.
Speech-Language pathologist - health professional trained to evaluate and treat people who have voice, speech, language, or swallowing disorders (including hearing impairment) that affect their ability to communicate.
Stroke - also known as a cerebrovascular accident (CVA); caused by a lack of blood to the brain, resulting in the sudden loss of speech, language, or the ability to move a body part, and, if severe enough, death.
Stuttering - frequent repetition of words or parts of words that disrupts the smooth flow of speech.
Sudden deafness - loss of hearing that occurs quickly due to such causes as explosion, a viral infection, or the use of some drugs.
Swallowing disorders - any of a group of problems that interferes with the transfer of food from the mouth to the stomach.
Syndromic hearing impairment - hearing loss or deafness that, along with other characteristics, is inherited or passed down through generations of a family.
Tactile - related to touch or the sense of touch.
Tactile devices - mechanical instruments that make use of touch to help individuals who have certain disabilities, such as deaf-blindness, to communicate.
Taste - sensation produced by a stimulus applied to the gustatory nerve endings in the tongue. The four tastes are salt, sour, sweet, and bitter. Some scientists indicate the existence of a fifth taste, described as savory.
Taste buds - groups of cells located on the tongue that enable one to recognize different tastes.
Taste disorder - inability to perceive different flavors. Taste disorders may result from poor oral hygiene, gum disease, hepatitis, or medicines and chemotherapeutic drugs. Taste disorders may also be neurological.
Throat disorders - disorders or diseases of the larynx (voice box), pharynx, or esophagus.
Thyroplasty - surgical technique to improve voice by altering the cartilages of the larynx, which houses the vocal folds (vocal cords), in order to change the position or length of the vocal folds. Also known as laryngeal framework surgery.
Tinnitus - sensation of a ringing, roaring, or buzzing sound in the ears or head. It is often associated with many forms of hearing impairment and noise exposure.
Tongue - large muscle on the floor of the mouth that manipulates food for chewing and swallowing. It is the main organ of taste, and assists in forming speech sounds.
Touch - tactile sense; the sense by which contact with the skin or mucous membrane is experienced.
Tourette syndrome - neurological disorder characterized by recurring movements and sounds (called tics).
Tracheostomy - surgical opening into the trachea (windpipe) to help someone breathe who has an obstruction or swelling in the larynx (voice box) or upper throat or who has had the larynx surgically removed.
Tuberous Sclerosis - Hereditary disease with multiorgan manifestation. Typical symptoms are epileptic seizures, autism, skin disorders, and renal tumors.
Tympanoplasty - surgical repair of the eardrum (tympanic membrane) or bones of the middle ear.
Umami - Taste of substances such as L-glutamate salts (MSG) that are found in foods like bouillon and other stocks.
Usher syndrome - hereditary disease that affects hearing and vision and sometimes balance.
Velocardiofacial syndrome - inherited disorder characterized by cleft palate (opening in the roof of the mouth), heart defects, characteristic facial appearance, minor learning problems, and speech and feeding problems.
Vertigo - illusion of movement; a sensation as if the external world were revolving around an individual (objective vertigo) or as if the individual were revolving in space (subjective vertigo).
Vestibular Neuronitis - infection at the vestibular nerve.
Vestibular system - system in the body that is responsible for maintaining balance, posture, and the body's orientation in space. This system also regulates locomotion and other movements and keeps objects in visual focus as the body moves.
Vestibule - bony cavity of the inner ear.
Vibrotactile aids - mechanical instruments that help individuals who are deaf to detect and interpret sound through the sense of touch.
Vocal cord paralysis - inability of one or both vocal folds (vocal cords) to move because of damage to the brain or nerves.
Vocal cords (Vocal folds) - muscularized folds of mucous membrane that extend from the larynx (voice box) wall. The folds are enclosed in elastic vocal ligament and muscle that control the tension and rate of vibration of the cords as air passes through them.
Vocal folds - see Vocal cords.
Vocal tremor - trembling or shaking of one or more of the muscles of the larynx, resulting in an unsteady-sounding voice.
Voice - sound produced by air passing out through the larynx and upper respiratory tract.
Voice disorders - group of problems involving abnormal pitch, loudness, or quality of the sound produced by the larynx (voice box).
Waardenburg syndrome - hereditary disorder that is characterized by hearing impairment, a white shock of hair and/or distinctive blue color to one or both eyes, and wide-set inner corners of the eyes. Balance problems are also associated with some types of Waardenburg syndrome.
All text of this article available under the terms of the GNU Free Documentation License (see Copyrights for details).
Diseases and medical conditions of the ear and auditory system