Definitions of commonly used audiology terms.

 

Aditus – opening between the pneumaticized mastoid air cells and the middle ear space.

 

American Academy of Audiology – Largest of the professional organizations for audiologists.

 

American Speech-Language Hearing Association – Professional organization for both speech-language pathologists and audiologists. 

 

Amplifier – a device that increases the intensity of the sound

 

Amplitude – the amount of displacement of something; the amount of movement.  Example: the amplitude of the vibration of the air molecules is the distance back and forth of the vibration.  Related to the intensity of the sound.

 

Ampulla – the enlarged section of the semicircular canal in which the sense organ for head rotation is located.

Anatomy – the study of the structures of the body.

 

Antagonistic – pulling in opposite directions.  The contraction of the stapedial muscle and tensor tympani are antagonistic.

 

Antihelix – part of the pinna that is just beyond the concha; it is a rim of cartilage.

 

Arch of Corti – also called pillars of Corti.  Supporting structure located between the inner and outer hair cells within the organ of Corti.

 

Areal ratio – the relative difference in the size of the tympanic membrane to the stapes footplate.  Because of this size difference, sound is concentrated as it reaches the inner ear, and the sound pressure is enhanced by about 27 dB.

 

Au.D. – Professional doctoral degree designator for audiologists.  Fellowship status for new members of the American Academy of Audiology and certification of new members by the American Speech-Language Hearing Association will require a doctoral degree in 2007.

 

Audiologist – health care professional responsible for the assessment and management of persons with hearing and/or balance disorders.

 

Audiology – the science of the assessment and management of hearing and balance disorders.

 

Audiometer – electronic device used to assess hearing.  Produces pure-tone signals at calibrated intensities and allows for controlled presentation of speech signals to the patient’s ears.

 

Auricle – synonym for the pinna.  Portion of the external ear that gathers sound waves and funnels them to the external auditory meatus.

 

Axon – portion of a neuron than conveys the neural impulse away from the cell body to the terminal button.

 

Basilar membrane – membrane inside the cochlea that separates scala media and scala tympani; on this membrane rests the organ of Corti.

 

Brainstem – portion of the brain that is below the cerebrum and anterior to the cerebellum.  It is a conduit of information to the “brain” and to the cerebellum (the cerebellum coordinates motor function.)

 

Calibration – the process of determining that an audiometer produces the desired signals, at the proper intensities.

 

Cartilaginous – comprised of cartilage, a dense but flexible connective tissue.

 

Cerebellopontine angle – area where the VIII nerve enters the brainstem.  At this location, the auditory pathway takes a turn (angles) upward.  This occurs at the junction of the cerebellum and pons portion of the brainstem, ergo the name.

 

Cerumen – earwax.  Substance produced by the glands under the hairs in the cartilaginous portion of the external auditory meatus.  Comprised of the secretions of the apocrine and sebaceous glands.

 

Cilia – tiny hairlike projections on a cell.  Ciliated cells are found in portions of the middle ear space, the Eustachian tube, and in the cochlea.  Cilia are found on both outer and inner hair cells.

 

Cochlea – spiral-shaped hole in the temporal bone.  It is here that sound energy is received by the hair cells and the nerve impulses that encode hearing are created.

 

Cochlear nucleus – Group of nerve cells just medial to the VIII nerve.  The first nucleus in the auditory pathway.

 

Compression – also called condensation.  The portion of a sound wave where the air molecules are most tightly packed together.  See also the tutorial on acoustic review.

 

Concha – portion of the pinna that is the recessed bowl.

 

Condensation – also called compression.  The portion of a sound wave where the air molecules are most tightly packed together.  See also the tutorial on acoustic review.

 

Cortex – outside portion of the cerebrum, consisting of gray matter (material that is mostly cell bodies, rather than white matter, which is mostly myelinated neurons).

 

Crus – singular (crura is plura), from the Latin word meaning leg, it is a side part of the stapes bone of the middle ear.

 

Decibel – (dB) the unit for measuring the intensity of sounds.  Technically, it is a ratio of two pressures or intensities that indicates how much larger one sound is than another, expressed in logarithmic units.  For this reason, the type of decibel should be stated unless one is stating that the sound is a given number of decibels louder than another sound.  Types of decibels include dB HL, dB SPL, and dB SL.

 

dB HL – decibels hearing level.  0 dB HL is the softest sound that can be heard by the average person with normal hearing.  It is not the absence of sound, as persons with better than average hearing will have thresholds lower than 0 dB HL (e.g. –10 dB HL).

 

dB SL – decibels sensation level.  The number of decibels above another threshold.  See tutorial understanding the acoustic reflex.

 

dB SPL – decibels sound pressure level.  The type of decibel used in sound level meters, it compares the pressure of sound at the microphone of the sound level meter to the reference pressure of .0002 dynes/cm2.

 

Decussation – crossing over of nerve fibers from one hemisphere of the brain to the opposite (contralateral) hemisphere.  Auditory nerves will decussate at several places in the brainstem.

 

Dendrite – portion of the neuron that connects either to the sensory receptor (i.e. hair cell) or to the terminal button of the neuron that is transmitting information (the neuron that comes “before” in the auditory system).

 

Eardrum – colloquial term for tympanic membrane.

 

Earmold – the portion of a behind-the-ear style hearing aid that fits in the concha and directs the sound into the ear canal.

 

Endolymph – fluid in the section of the cochlea known as scala media, and in the membranous labyrinth of the vestibular system.  This fluid is high in potassium and relatively low in sodium.

 

Eustachian tube – tube, which is normally closed, between the nasopharynx and the middle ear system.  It is opened by contraction of the levator veli palatini and tensor veli palatini during swallowing and yawning.

 

External ear – part of the auditory system comprised of the pinna and external auditory meatus.

 

Footplate – portion of the stapes bone that is attached to the two crura and that sits in the oval window.

 

Frequency – the number of back and forth vibrations of a vibrating object in one second.  Related to pitch; the larger the frequency of vibration the higher the pitch.

 

Hearing aid – device that amplifies sound for a hearing-impaired patient.  It is worn in or behind the ear.

 

Hearing aid dispenser – person licensed by the state to dispense hearing aids, but who does not have university training in audiology.

 

Helicotrema – the portion at the apex of the cochlea where there is no scala media.  The perilymph can flow between scala tympani and scala vestibuli at this location.

 

Helix – the outside rim of cartilage that runs along the top of the ear.

 

Hertz – (Hz) measure of the frequency of sound, the number of back and forth vibrations in one second of time. 

 

Impedance – an object or medium’s resistance to energy flow.  A high-impendance medium will reject energy; a low-impedance substance vibrates more freely.

 

Incus – one of the ossicles, or bones of the middle ear.  It is the middle bone, located between the malleus and the stapes.

 

Inferior colliculus – One of the nuclei of the auditory system, it is located superior to the lateral lemniscus but before medial geniculate body.

 

Inner ear – fluid-filled hole in the temporal bone containing the sense organs for hearing and balance.

 

Inner hair cells – the cells within the organ of Corti that are responsible for encoding neural impulses for sound.  These ciliated cells are located on the medial side of the arch of Corti, and are found spiraling the length of the cochlea.  Only one hair cell is seen on any cross section of the cochlea, where 3 to 5 outer hair cells are found sitting side by side.

 

Intensity – the loudness of sound; related to the amplitude of the sound vibration.

 

Internal auditory meatus – the hole in bone through which the nerves exit the cochlea on their way to the brainstem.

 

Kilohertz – (kHz). Thousands of hertz (cycles per second of vibration).  A measure of the frequency of sound.

 

Lateral lemniscus – nucleus of the auditory system located after superior olive, but prior to inferior colliculus.

 

Lateralization – the perception that sound is in one ear or the other when presented by headphones or via bone conduction.  See also localization.

 

Lever action of the ossicles – the increase in force of the movement of the incus (and thus the stapes footplate in oval window) that is attributable to the fact that the malleus is longer than the incus, and thus, like a lever, it moves the incus with greater force, though a shorter distance.

 

Levator veli palatini – muscle of the nasopharynx, one of those responsible for opening the Eustachian tube.

 

Localization – the ability of a person to determine the location of a sound source that is present in soundfield (somewhere out in the room).   See also lateralization, a related term, meaning to perceive the sound in one ear or the other when presented by earphones or bone conduction.

 

Malleus – one of the ossicles, or bones of the middle ear.  It is the first bone, and is attached to the tympanic membrane and connected to the incus. 

 

Manubrium of the malleus – portion of the malleus that attaches to the tympanic membrane; the “handle” of the malleus.

 

Mastoid air cells – openings in bone, filled with air, that are linked to the middle ear space.  The opening between the middle ear and pneumaticized (air-filled) mastoid cells is the aditus.

 

Mastoid bone – portion of the temporal bone that is located behind the pinna.

 

Mastoid process – the dome-shaped portion of the mastoid bone that is behind the pinna.  It is the location for the placement of bone-conduction oscillators. 

 

Medial geniculate body – auditory nucleus located in the brainstem, above the inferior colliculus.  It is the last nucleus before the auditory signal reaches the cortex.

 

Medium – The substance through which sound travels.  Sound is often defined as the vibration of the molecules of a medium.  Air is the most common medium.

 

Microphone – device that is set into vibration by sound waves, and will convert the sound energy into an electrical signal that represents the frequency and amplitude of the sound striking the microphone’s diaphragm (thin metal sheet that picks up the vibrations).

 

Middle ear – the air-filled hole in bone containing the ossicles and the tendons of the two muscles of the middle ear.  Some people classify the tympanic membrane as being a part of the middle ear.

 

Modiolus – the center core of the cochlea.  The first-order neurons (VIII nerve) runs through modiolus before exiting via the internal auditory meatus.

 

Molecule – Smallest particle of a chemical element.  Hydrogen, nitrogen and oxygen are examples of molecules.  Molecules are comprised of protons, electrons and neutrons.

 

Mucous membranes – type of lining of the middle ear and nasopharynx.  It secretes mucus, a secretion of water, salts, skin tissue cells, white blood cells, and a protein called mucin.

 

Myelin – a fatty material that covers portions of some neurons’ axons.  Myelin insulates nerves from each other, and permits rapid transmission of neural impulses as neural signals (action potentials) “skip” across myelin sheathes, jumping from one node of Ranvier to the next.

 

Node of Ranvier – unmyelinated segments of axons, between the myelin sheathes that cover the axon.  The action potential is conducted from one node to the next, allowing for a faster depolarization wave than would occur in the neuron were not myelinated.

 

Organ of Corti – the collection of cells, sitting on basilar membrane, that permit the sound waves to become coded as nerve impulses.  The organ of Corti includes inner and outer hair cells, the supporting cells, including the arch of Corti, the tectorial membrane and spiral limbus.

 

Osseous spiral lamina – a ridge of bone projecting from the core of the cochlea (modiolus) inward towards basilar membrane. 

 

Otolaryngologist – Physician who specializes in the medical disorders of the ears, nose and throat, also called an ENT physician.

 

Outer ear – section of the ear that includes the pinna and external auditory meatus.

 

Outer hair cells – the cells within the organ of Corti that are responsible for increasing the amount of basilar membrane movement when soft sounds are present.  These ciliated cells are located on the radial side of the arch of Corti, and are found spiraling the length of the cochlea.  Three to five outer hair cells sit side-by-side when viewing a cross section of the cochla.  The cilia of the outer hair cells are embedded in tectorial membrane.

 

Oval window – membrane-covered opening between the middle ear and scala vestibuli of the inner ear.  Stapes footplate sits in oval window.

 

Pars tensa  - portion of the tympani membrane that contains the fibrous middle layer and comprises most of the area of the tympanic membrane.  See also pars flaccida.

 

Pars flaccida – the portion of the tympanic membrane that does not contain a fibrous middle layer, but only has the skin and mucous membrane layers.  It is located at the top of the tympanic membrane.

 

Perilymph – the inner ear fluid found in scala vestibuli and scala tympani.  This fluid is high in sodium and relatively low in potassium.

 

Period – the time required for one complete cycle of vibration to occur.

 

Phase – Describes the amount of compression or rarefaction of a sound.  Sounds at 90 degrees phase are at maximal compression; those at 270 degrees phase are maximally rarefied.  Phase cycles from 0 to 360 degrees.

 

Physiology – the study of the function of the body, that is, how things work.

 

Pinna– synonym for the auricle.  Portion of the external ear that gathers sound waves and funnels them to the external auditory meatus.

 

Physics – the study of the physical properties of matter and energy.  Acoustics is a branch of physics that studies how sound vibration occurs.

 

Pure tone – a sound that has only one frequency.  It occurs when an object is vibrating in simple harmonic motion.  See also tutorial on acoustics review.

 

Rarefaction – The portion of a sound wave where the air molecules are most spread apart and have the lowest pressure.  See also the tutorial on acoustic review.

 

Reissner’s membrane – the membrane separating scala media and scala vestibuli in the cochlea.

 

Resonance – enhancement of sound at a certain frequency because of the characteristics of the vibrating object or tube.  Cavities of different lengths resonate, or accentuate sound vibration, at certain frequencies.  Objects will vibrate best at a given frequency or frequency range, depending upon the mass and stiffness of the object.

 

Round window – membrane-covered opening between the scala tympani of the inner ear and the middle ear.

 

Saccule – located in the vestibule of the inner ear, this structure along with the utricle sense “straight line” head motion.

 

Scala media – the middle section of the cochlea, which contains endolymph.  Basilar membrane is at the bottom of scala media; Reissner’s membrane is at its top.

 

Scala tympani – the section of the cochlea that is below basilar membrane and contains perilymph.  If a cross section of one coil of the cochlea is examined, scala tympani will be on the bottom.

 

Scala vestibuli – the section of the cochlea that is above Reissner’s membrane and contains perilymph.  If a cross section of one coil of the cochlea is examined, scala vestibuli will be on the top.

 

Semicircular canals – the 3 channels in the vestibular section of the inner ear that permit neural encoding of head rotation.

 

Shrapnell’s membrane – a synonym for pars flaccida.

 

Simple harmonic motion – the vibration back and forth of an object or air molecules that results in a clean single tone, a “pure tone”.  See also tutorial on acoustics review.

 

Soma – the body of a nerve cell.

 

Speech-language pathologist – health care professional who assess speech and language development and treats language and speech disorders.

 

Spiral limbus – a part of the organ of Corti that is one point of attachment for tectorial membrane.  It is composed of periosteum, the type of tissue that covers bone, and is located on top of the bony ridge called osseous spiral lamina.

 

Stapedius – a muscle residing in the pyramidal eminence on the posterior wall of the middle ear space whose tendon is attached to the neck of the stapes.  Contraction of the stapedial muscle (e.g. in response to loud sound) increases the stiffness of the middle ear system and reduces the transmission of low-frequency sound through the middle ear.

 

Stapes – one of the ossicles, or bones of the middle ear.  It is the last bone, located after the incus.  The footplate of the stapes is attached to the oval window of the inner ear.

 

Stria vascularis – a lining of the radial wall of scala media, containing a rich network of vascularized tissue (containing networks of small veins and arteries).  Endolymph is produced and nourished by stria vascularis. 

 

Superior olivary complex – a nucleus in the auditory central nervous system, located just after cochlear nucleus and prior to lateral lemniscus.

 

Tectorial membrane – a gelatinous tissue mass that is located above the hair cells.  The cilia of the outer hair cells imbeds in tectorial membrane.

 

Temporomandibular joint – (TMJ), the hinge joint for the jaw.

 

Tensor tympani - a muscle residing in the semicanal of tensor tympani on the medial wall of the middle ear space whose tendon is attached to the malleus.  Contraction of the tensor tympani muscle would move tympanic membrane inward and decrease the vibration of the TM by increasing the stiffness of the middle ear system.   However, in humans this muscle does not appear to contract in response to loud sounds. 

 

Tensor veli palatini – muscle of the nasopharynx, one of those responsible for opening the Eustachian tube.

 

Tonotopic organization – the property of a structure to be organized such that different locations within the structure respond to or encode different frequencies.  (There is a different place within the structure for each frequency.)

 

Tragus – the skin covered appendage in front of the pinna.  The tragus can be pushed inward to cover the entrance of the ear canal.

 

Trapezoid body – nerve fiber pathway in the lower brainstem that decussates from one hemisphere to the other.  The trapezoid body contains a nucleus, called the nucleus of the trapezoid body.

 

Traveling wave – an undulating up and down motion of basilar membrane in response to sound that increases in amplitude relatively gradually until it reaches a maximum displacement point, and then decreases in amplitude rapidly just apical to that point of maximum vibration.

 

Tunnel of Corti – space beneath the arch of Corti.

 

Tuning fork – hand-held device that produces tones that are essentially pure tones.  Tuning forks of different sizes produce different frequency tones.

 

Tympanic membrane – also called the eardrum colloquially, this membrane separates the outer and middle ear.

 

Umbo – the center-most point of the tympanic membrane and the point at which the tympanic membrane is most medially displaced.  The manubrium of the malleus is attached at the umbo, and its medial pull creates the cone shape of the eardrum.

 

Utricle – located in the vestibule of the inner ear, this structure along with the saccule sense “straight line” head motion.

 

Vestibular system – portion of the inner ear responsible for encoding information about head movement and head position.

 

Vestibule – portion of the inner ear that is between the cochlea and the semicircular canals.  Oval window is located in the vestibule.

 

VIII nerve – also called the acoustic nerve or more correctly, the vestibulo-acoustic nerve.  It conveys information from the cochlea, utricle, saccule and semicircular canals to the brainstem.

 

Wavelength – when a pure tone is produced, the sound radiates outward.  As it does, different areas (of air) are in rarefaction and compression.  Wavelength is the physical distance, generally measured in feet, between areas where the sound wave is in the same phase of vibration.  For example, if air molecules are in maximal compression at one place, and then are rarefied one foot later, then maximally compressed again two feet away from that original compression place, then the wavelength is 2 feet.  Wavelength is related to frequency and computed by dividing the speed of sound by the frequency.