Audiology Test One
Terms
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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
- Malleus
- 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
- perilymph
- cochelar fluid in scala vestibuli, scala tympani, and spaces of organ of Corti. High in Na and Ca. similar to CSF
- Endolymph
- 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
- modiolus
- central bony pillar, blood vessels and nerve fibers course
- heliotrema
- passage connect the scala tympani and scala vestibuli
- utricle
- large of two sac like struc. in vestibule contains macula responsive to linear acceleration.
- saccule
- 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
- cortilymph
- fills spaces below the reticular lamina, high Na-needed for function of hair cells and nerve fibers in organ of corti
- tonotopic
- Core fibers arise from the apex of cochlea (low frequency) and outer fibers arise from the base of the cochlea (high frequency)
- CN VIII
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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
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Three divisions
Dorsal
Anterior ventral
Posterior ventral
Afferent connections in AVCN and PVCN
Efferent connections in DCN - Reticular formation
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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
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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
- localization
- medial geniculate body
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Last subcortical center
Ventral portion specific for auditory information.
Multi-sensory neurons
Intergration of sensory information
Auditory radiations take information to brain. - Auditory cortex
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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.
- promontory
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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
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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
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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
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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
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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
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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
- afferent
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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 - efferent
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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
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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