Chapter 19: Anatomy & Physiology of Hearing

• Outer (External) Ear


  the concave, somewhat funnel-like structure that collects, resonates, and directs sound waves to the tympanic membrane, assists in localizing the direction from which sound is coming, and helps protect the middle ear; composed of the auricle (pinna), ear canal, and outer layer of the tympanic membrane
• Tympanic Membrane (Eardrum)


  a thin, semitransparent membrane that separates the ear canal from the middle ear and transmits sound vibrations into the middle ear
• Cerumen


  a yellowish or brownish waxy secretion produced by ceruminous glands in the ear canal that protects the ear canal from intrusion by insects
• Hearing Threshold


  In audiometry, the level at which a stimulus sound, such as a pure tone, is barely perceptible; usual clinical criteria demand that the level be just high enough for the subject to be aware of the sound at least 50% of the time it is presented.
• Middle Ear


  an air-filled chamber located within the temporal bone of the skull; beginning at the inner side of the tympanic membrane and attaching the ossicular chain to the oval window of the cochlea
• Ossicular Chain


  the three small bones (ossicles) of the middle ear named after their basic shapes: malleus (for the mallet/hammer), incus (for the anvil), and stapes (for the stirrup)
• Barotrauma


  a feeling of fullness or pressure in the middle ear as a result of ascending or descending with changes in altitude. symptoms may include general ear discomfort, fullness or stuffiness in the ear, difficulty hearing and dizziness. Prolonged barotrauma may result in ear pain, nosebleed, moderate to severe hearing loss and in some severe cases, rupture of the tympanic membrane. Ear barotrauma is dangerous when the eustachian tubes are occluded, such as from an upper respiratory infection or allergies
• Valsalva Maneuver


  the procedure of closing the mouth and pinching the nostrils closed with the fingers and forcefully exhaling air, usually causing the Eustachian Tubes to open and air to flow into the middle ear to equalize middle ear cavity air pressure with atmospheric air pressure.
• Cochlea


  the part of the inner ear containing the sensory mechanism of hearing; a spiral tunnel with 2 3/4 turns about 30 mm long, resembling a tiny snail shell
• Vestibular System


  the inner ear structures associated with balance and position sense, including the vestibule and semicircular canals of the vestibular mechanism, with interactions of the visual and proprioceptive systems and connection to the cerebellum
• Cochlear Implant


  a device that enables individuals with profound hearing loss to perceive sound through an array of electrodes that are surgically implanted in the cochlea and deliver electrical signals to the vestibulocochlear nerve, and an external amplifier that activates the electrode array
• Primary Auditory Cortex (Heschl's Gyrus)

  the portion of the posterior superior region of both temporal lobes (Heschl's Gyrus) that receives auditory signals from the ears and processes the signals as environmental sounds, human speech sounds, and human nonspeech sounds
• Differential Threshold


  the smallest difference that can be detected between two auditory signals
• Hearing Sensitivity Impairment


  the most common type of hearing loss; a reduction in the sensitivity of the auditory mechanism that results in sounds needing to b e a higher intensity than normal before they can be heard by the listener.
• Auditory Nervous System Impairment

  the result of reduced ability to clearly hear sounds above the hearing threshold; occurs less often than hearing sensitivity impairments, which may occur concurrently, causing a dual hearing problem
• Mixed Hearing Loss


  a reduction in hearing because of a combination of a disordered outer or middle ear and inner ear
• Otitis Media with Effusion


  any inflammation or infection of the middle ear, particularly common in childhood and often associated with a common cold, allergies, sinus infections, and sore throats. Eustachian tube malfunction typically is the physiological cause; effusion – the escape of fluid from tissue as a result of seepage.
• Mastoiditis


  an infection of one of the mastoid bones (just behind the ear) that is usually an extension of a middle ear infection; characterized by earache, fever, headache and malaise; medical treatment may require intravenous antibiotics for several days, and residual hearing loss may follow the infection
• Otologist


  a physician who is first trained in otolaryngology (ENT) and then specializes in diagnosis and treatment of diseases and other disorders of the ear
• Pressure-equalizing (PE) Tube


  A small silicone tube inserted into the tympanic membrane following a myringotomy to equalize air pressure between the middle ear cavity and the atmosphere as a substitute for a nonfunctional Eustachian Tube
• Adenoids (Pharyngeal Tonsils)


  lymphoid tissue found on the pharyngeal wall in the nasal-pharyngeal region. They begin to develop at about 6 months of age and may continue to grow and possibly interfere with or occlude the openings of the Eustachian Tubes. When enlarged, adenoids may block the passage of air from the nasal cavity into the pharynx, preventing normal nasal breathing and requiring mouth breathing. They are sometimes surgically removed to allow nasal breathing and help prevent middle ear infections.
• Otosclerosis


  typically a hereditary condition that occurs when there is growth of bony tissue around the footplate of the stapes that presses against the oval window, resulting in a conductive hearing loss, and causing attenuation in the cochlea
• Ototoxic


  drugs that have harmful effects on the central auditory nervous system, including aspirin, aminoglycoside antibiotics, furosemide, and quinine
• Noise-induced Hearing Loss


  a permanent sensorineural hearing loss caused by exposure to excessive loud noise, often over long periods of time
• Acoustic Trauma


  damage to hearing from a transient, high-intensity sound
• Tinnitus


  a subjective noise sensation, often described as a ringing, roaring, or swishing in the ear that may be heard in one or both ears. Associated with a variety of hearing disorders in both adults and children. Can affect concentration, sleep, education, employment, relationships, etc.
• Meniere's Disease


  a chronic disease of the inner ear characterized by recurrent episodes of vertigo, tinnitus, and sensorineural hearing loss that may be bilateral
• Presbycusis


  hearing loss associated with old age, usually involving both a loss of hearing sensitivity and a reduction in clarity of speech