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Audiology Test One


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Fact about middle ear
filles w/ air, must be equal press. to funct. correctly, 2cm squared, irregular shaped, Two sections: cavity proper:tympanum and attic
Function of middle ear
transmit acoustic energy from the tympanic membrane to oval window via ossicles
General Function ME
impedance mathing device for inner and outer ear-because sound travels more effic. through air than water.
Structure of ME
Eustachian tube, tympanic membran, ossicluar chain,Middle Ear muscles,
Eustachian Tube Function
equaliz press. inside and outside the tympanic membrane. Provides need O2 to Middle ear space and drains fluid.
Eustachian Tube General
opens 1/min awake and 1/5 min while asleep. Moving from less air press. to great air pressure is more dramatic
Rest state Eustachian Tube
closed to prevent presure changes during respiration and to prevent own voice being too loud
How can ET be opened
yawning,swallowing, airplane, mountains, wiggling ears-if it stays closed during pressure change it can burst TM.
TM general
85-90mm squared 55mm squared vibrates-17x's the size of the oval window, drum shaped(max acoustic pickup), tip of malleus in center
TM job
Changes sound into mechanical energy, umbo is gathering place and approx. center of TM
Ossicular Chain Anatomy
2-6mm-ossicles suspended in the middle ear-three bones-smallest bones in the body: Malleus, Incus, and Stapes
Ossicular Chain funct.
provides a lever system to rotate malleus and incus to drive the sttapes into inner ear-vibration from TM starts process
Most lateral ossicle Manubrium-in TM, Neck-narrow part, Lateral process-visible bulge TM, head-connects w/ body of incus
Malleus and Incus
connect w/ double saddle joing-incudomallear articulation-which allows two bones to move as one
Incus and Stapes
Lenticular process of the incus articulates w/ the head of the stapes w/ ball and socket joint called incudostapedial joint.
Structures of the ME
Tympanic membrane, ossicular chain, eustachian tube, stapedious muscle, tensor tympani, round window, oval window, promontory, tegman tympani
CANS structures
CN VIII cochlear nucleus,sup. olivary complex,lateral leminicus,inf colliculus, med. geniculate body, auditory cortex
Inner Ear Structures
cochlea, vestibules, and semicircular canals
Cochlea structures
spiral ganglion, scala ympani, scala media, scala vestibuli,organ of corti,basilar membrane, reissner's membran, spiral lamina, modiiolus, heliotrema, utricle, ihc, and ohc
Vestibular system structures
ductus reuniens, cochlear duct
spiral ganglion
cell bodies of CN VIII within the modiolus
cochelar fluid in scala vestibuli, scala tympani, and spaces of organ of Corti. High in Na and Ca. similar to CSF
in scala media high K and low Na bathes gelatanous structures of inner ear
Scala media
middle channel of cochlear duct filled w/ endolymph bordered by basilar mem., reissner's mem. and spiral ligament
Scala Vestibuli
uppermost channel of cochlear duct filled w/ perilymph terminates at the heliotrema and basally at oval window.
organ of corti
hearing organ made of sense and supporting cells on the basilar membrane
basilar membrane
base of mem. labryinth divides it into the scala vestibuli and scala tympani support scala media and organ of Corti
Reissner's membrane
attached to osseous spiral lamina separates the scala vestibuli and scala media
Spiral Lamina
shelf of bone arising from modiolar side of the cochlea, nerve fibers tral to and from hair cells
central bony pillar, blood vessels and nerve fibers course
passage connect the scala tympani and scala vestibuli
large of two sac like struc. in vestibule contains macula responsive to linear acceleration.
part of vestibular system
endolymphatic sac
responsible for absorption to the relieve endolymphatic hydrops
semicircular canals
three canals in the osseous labyrinth of the vestibular sensor tissue for angular motion
ductus reuniens
tube connect the saccule to the scala media, carries endolymph bt vestibule and aud. mem. labyrinth
cochlear duct
spiral mem. canal that is the cochlear portion of the mem labyrinth.
stria vascularis
highly vascularized band of cells of internal surface of spiral ligament w/in scala media
claudius cells
support OHC on lateral side
Henson cells
support cells of organ of corti which the edge of tectorial mem. is attached
dieter cells
large cell bodies of organ of corti rest on Basilar mem. extend to cradle the bases of ohc
Outer hair cells
motile cells w/in organ of corti efferent inntervation, responsilbe for fine tuning freq. and potentiating the sensitivity of IHC.
Outer hair cell appearance
three row,w-shaped, humans have about 12,000, elongated, tube shaped, muscle proteins, like an amplifier
Inner hair cells
sense cells arrange in single row on organ of corti, primarly afferent human's have about 3,500
inner hair cells appearance
flask shaped, like a microphone
reticular lamina
formed by tops of hair cells
fills spaces below the reticular lamina, high Na-needed for function of hair cells and nerve fibers in organ of corti
Core fibers arise from the apex of cochlea (low frequency) and outer fibers arise from the base of the cochlea (high frequency)
Enters the brain at the pontomedulary junction
Has 30,000 nerve fibers
Type I: Large Bipolar cells, connect IHCs, 95% axons connected to the IHCs
Type II: Small pseudobipolar cells, 5 % axons connected to the OHCs
cochlear nucleus
Three divisions
Anterior ventral
Posterior ventral
Afferent connections in AVCN and PVCN
Efferent connections in DCN
Reticular formation
Resides in center of brainstem
Control center for CNS. (sleep)
Communicates with virtually all areas of the brain.
Important in auditory alertness, reflexes, and habituation.
Superior Olivary complex
75% fibers cross over (decussation)
Allows for bilateral representation
Looks at differences in time and intensity between ears (localization)
Auditory reflex
lateral leminiscus
the highway
inferior colliculus
medial geniculate body
Last subcortical center
Ventral portion specific for auditory information.
Multi-sensory neurons
Intergration of sensory information
Auditory radiations take information to brain.
Auditory cortex
Temporal lobe (sides of the head)
Bilateral (both right and left hemisphere)
Primary (AI)
Frequency Information
Fining tuned cells
Secondary (AII)
Broad tuning
Association Areas
Round Window
Membrane covered opening into the labyrinthine wall of the ME Leading into the scala tympani, when cochlear implants are done the electrode is inserted through here.
Oval Window
opening in the labyrinthine wall of the ME, leads into the scala vestibuli of the cochlea, into which the footplate of the stapes fits.
Bony prominence of the labyrinthine wall of the middle ear cavity, separates the oval and round window
Facial nerve Canal: bony canal through which the facial nerve passes
Eustachian tube
Prime function is to equalize pressure inside and outside the TM. Also provides oxygen to Middle ear space and drains fluids.
Tube is normally closed to seal off ear from pressure changes during respiration
Prevent AUTOPHONY (person’s own voice is very loud)
Functions of earwax
It lubricates the ear
It is antimicrobial (kill germs)
It repels insects
Keeps ear free of debris. It traps dust and dirt particles and keeps them from reaching the Eardrum
Traveling wave theory
Bekesy won the Noble Prize for his work in human cadavers.
Frequency is coded by place
there is a difference in stiffness due to width.
The apex is wider and less stiff there for it produces low frequencies
The basal end is narrower and stiffer therefore is produces high frequencies
Otitis media
inflammation of the ME
predominately due to Eustachian tube dysfunction
most common cause of transient conductive hearing loss in children especially with effusion
Otitis media serous
common and is characterized by thin, watery, sterile fluid
Purulent / suppurative effusion contains pus
Nonsuppurative refers to serous or mucoid fluid
Mucoid refers to fluid that is thick, viscous
Sanguineous contains blood
otitis media chronic
refers to a case which persists beyond 8 weeks or results in permanent damage to ME mechanism
otitis media acute
is a single bout lasting fewer than 21 days
sensory-The innervation of the cochlea involves both efferent and afferent neurons.
Hair cells are connected to the auditory nervous system by synapses with auditory nerve fibers within the Organ of Corti.95% of afferent neurons supply the IHCs
motor-Receives efferent signals from the olivocochlear bundle from the superior olivary complex (SOC)
1600 fibers enter temporal bone along the vestibular branch of the VIII nerve and split off to enter the cochlea
These nerve endings contain vesicles of chemical neurotransmitter acetylcholine, mostly OHC
Hair cell activation
Bending stereocilia in one direction leads to excitation by stretching upward- pointing cross-links, which open a pore permitting ions to flow into the cell. This activates the air cell . Bending the stereocilia in the opposite direction causes inhibition because the pore closes
transmission of sound
Sound entering the outer ear hits the TM.
Vibrations of the TM are transmitted through the ossicles
Vibrations is represented as a rocked motion of the stapes footplate in the oval window
The inward and outward displacements of the oval window are transmitted to the cochlear fluid
ME system modifies the sound through resonance, directional effects, pinna effect and area/impedance matching
acoustic reflex
reflexive middle ear muscle contraction which occurs in response to high levels of sound stimulation. In humans, this is principally a stapedius reflex, while the tensor tympani contracts as part of a start reaction to very intense sounds
structures of outer ear
helix, darwin tubercle, antihelix, crura, crura of antihelix, triangular fossa, scaphoid fossa, concha, tragus, antitragus, lobule
TM structures
cone of light, pars tensa, pars flaccida, manubrium of malleus, umbo, annular ligament

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