Audiology Exam 1

Label (a, b, c, e, h, k)

a pinna

b external auditory canal

c tympanic membrane

e eustachian tube

h cochlea

k semicircular canals

Label (a, c, d, e, f, g, i)

a Reissner's Membrane

c scala media

d tectorial membrane

e Organ of Corti

f Basilar Membrane

g Scala Tympani

i scala vestibuli

List the three ossicles beginning at the tympanic membrane.

 malleus, incus, stapes

5 Divisions of the Ear

1. Outer (pinna, external auditory meatus)

2. Middle (eardrum, ossicles, eustachian tube)

3. Inner (vestibular for balance-semicircular canals, auditory for hearing-cochlea)

4. Auditory nerve (sends signal to brain)

5. Central nervous system (interprets signal)

Anatomical Planes

sagittal- divides right and left

coronal- divides front and back

transverse- divides top and bottom

Label

• Tympanic

• Petrous-houses cochlea

• Mastoid

• Squamous

Outer Ear- parts and functions

Pinna and Ear canal/EAM

Functions:

protection

funnel sound

timing (localize sound) and intensity (emphasizes certain frequencies)

mechanism of resonance- prolongation of sound through reflection or reverbation

transfer of function- enhances certain frequencies by outer ear contributing 15-20dB at tympanic membrane

Label Middle Ear

• Tympanic Membrane- 3 layers (epithelial-continuous of ear canal, middle-fibrous, inner mucosal- continuous with lining of tympanic membrane in middle ear)

▫ Malleous

 Manubrium

▫ Umbo

▫ Cone of Light- light from otoscope, point to nose, light on the right = right ear

▫ Pars Flaccida- no middle layer

▫ Pars Tensa- has fibrous middle layer

• Ossicular Chain

• Eustachian Tube

Muscles of Middle Ear

Stapedius and Tensor Tympani

both make up acoustic reflex, initiated at 80 dB as a protective mechanism but not a true protective mechanism because they only perform a pulling motion, they don’t vibrate

Eustachian Tube

Resting/normal state= closed

opens multiple times daily by the tensor veli palatini to allow the middle ear to maintain atmospheric pressure, it helps pressure equalization

Infants (180 degrees) Adult (45 degrees)

since infants eustachian tube is at less of an angle, there is less fluid drainage so they get more ear infections

Inner Ear Structures

bony and membranous, attached to temporal bone

semi circular canals- sense movement of head in space, balance

1. anterior

2. posterior

3. horizontal

Vestibule (encompasses utricle and saccule)-between cochlea and semi circular canals, balance

1. utricle

2. saccule

Cochlea- 2 ¾ turns, hearing

Cochlea

2 ¾ turns

Basilar membrane is inside the cochlea

narrow base with high frequencies

wide apex with low frequencies

Cross section of cochlea-know image

Chambers

1. scala vestibuli- filled w/ perilymph, fills bony portion of cochlea, similar to CSF, Sodium up, Potassium down

2. scala media- filled w/ endolymph (positive, similar to intracellular fluid, high potassium), houses organ of corti

3. scala tympani- filled w/ perilymph, fills bony portion of cochlea

sound traveling to ear pathway

• Pinna funnels acoustic energy into the external auditory meatus

• As sound waves travel through the EAM, they are compressed and gain ~20 dB

• This acoustic energy sets the tympanic membrane into motion, which then sets the ossicles (malleus, incus, stapes) into motion, and the acoustic energy is converted into mechanical energy

• Because the area of the tympanic membrane is so much larger than the area of the footplate of the stapes, this results in another 20-30 dB gain to overcome acoustic impedance

• The stapes pistons in and out of the oval window of the cochlea, which transfers the mechanical energy into the Scala vestibuli, which is fluid filled (perilymph). This disrupts the fluid, resulting in a fluid wave (energy is converted into hydromechanical energy at this point)

• Fluid wave travels up the Scala vestibuli reaches the helicotrema, where the Scala vestibuli joins the Scala tympani.

• Fluid wave then travels down the Scala tympani. As the fluid wave reaches the base, it hits the round window which stretches to release pressure - fluid here is still perilymph. This fluid wave sets the basilar membrane into motion which transfers the energy to the Scala media/organ of Corti and hair cells (fluid in the Scala media is endolymph). Reissners membrane moves the fluid in the scala media.

• Tectorial membrane brushes up against the hair cells. This stretches the tip links; energy is converted from hydromechanical to electrochemical. 

• As the tip links are stretched, potassium channels open and the cell is depolarized top to bottom. At the base, calcium channels open which releases neurotransmitters to the fibers of the auditory portion of CN VIII. This is where energy is converted to neurochemical.

• Inner hair cells-passive, 1 row(towards middle) and Outer hair cells-active, 3 rows, “W” (towards scala vascularis)

• Reticular lamina- covers top of hair cells for barrier between fluids

• Stereocilia- on top of hair cells ordered from shortest to tallest connected by cross links and tip links, tallest=killocillium

• Tectorial membrane- outer hair cells embedded here, inner are NOT

The separation of different fluids in the cochlea is very important to maintain the function of the cochlea itself; this is done by reissner’s membrane

shearing force

stereocillia have shearing force

shearing force moves towards kinocillium

tectorial membrane rubs against stereocilia, causing friction and moving to shear

therefore, causing depolarization of the hair cell

which causes the neuro signal to be sent along the nerve fibers, then go to the brain

hair cells

IHC- sends afferent (sensory info from body to brain)

OHC- sends efferent (motor info from brain to body), look like a “W”

Central Auditory Pathway

• Auditory nerve exits IAC

• Ascending pathway to the

brain

• Same nuclei on both sides

▫ Cochlear nucleus

▫ Superior Olivary Complex

▫ Lateral Lemniscus

▫ Inferior Coliculus

▫ Medial Geniculate

primary auditory cortex=herschels gyrus

What is a transducer, as it pertains to audiology?

 

Converts energy from one form to another

What type of transducer should you use if the patient has collapsing canals?  

inserts

What color is used for the left ear vs right ear? 

blue- Left

red- Right

What is the interaural attenuation values for headphones? Inserts? Bone Conduction? 

 

Headphones: 40dB; Inserts: 55 dB; Bone conduction: 0

Middle Ear-how many db boost

Once you hit the ear drum, you are in the middle ear (air filled that has to be equalized to hear perfectly)

converts acoustic vibrations into mechanical vibrations, which then sends to the ossicles

Impedance matching-get a boost of 33dB increase of loudness

the oval and round windows move in opposites allowing fluid in the cochlea to move correctly, therefore the middle ear is specifically designed to overcome mismatch between the air filled and fluid filled space-less important?

Acoustic Reflex-draw and explain function

Tensor Tympani and Stapedius

the acoustic relfex is a bilateral response triggered by loud noise

there is stiffening that reduces mobility of the ossicles, lowers SPL at oval window (10-20 dB SPL)

protection but also more so reduction of distortion which lowers the perceived volume of your own voice when you talk, making it easier to hear other sounds around you.

inner ear

The Hydro mechanical events in the Cochlea involve the movement of the Basilar membrane due to the traveling wave that we’ve elicited with the opposite movement of the oval and round windows. This is happening because of the stapes footplate opening and closing the oval window.

The chemical events in the cochlea relate to the changes in the hair cells cellular potentials as the stereocilia on the top of the hair cells bend and sheer with the movement of the basilar membrane

These are chemical changes that occur due to the very different types of fluids in the different parts of the Cochlea. The cellular changes cause a depolarization or an action potential. Which is going to cause The nerves of the cochlea to fire And then transmit sound to the eighth nerve up to the higher centers of the brain

tonotopical organization-high freq 1st at base/beginning of cochlea

cochlear potentials- stereocilia bathed and barrier

Stria vascularis maintains the highest endolymphic potential

Stereocilia are bathed in endolymph and there is perilymph at the base of the hair cell, the barrier is the recticular lamina

When the basilar membrane rubs against the stereocilia and opens the ion channels, there is an exchange of ions from the highly charged endolymph to the very negatively charged inner and outer hair cell fluid so the intracellular potential is negative but the flow of the positive potassium ions into the cell raises, the resting potential which causes depolarization

1. ion channels open after shearing force

2. game of telephone

3. back to rest

4. if tip links open channels long enough, fluid enters, depolarizes the cell, and action potential begins

outer hair cells

more rigid because they generate their own movement in response to the basilar membrane movement, therefore, the elongation of hair cells enhances the movement of basilar membrane allowing inner hair cells to make contact with the tectorial membrane and allows them to depolarize

the basilar membrane is specifically tuned to react best at certain frequencies

Frequency coding- 2 theories

freqeuncy theory- assumes there is a firing pattern that codes for the frequencies/pattern of discharge

place theory- frequency info coded where peak of traveling wave occurs

simple vibrations/sound transmission

sound=vibration

SOUND WAVES DO NOT PROPAGATE OR MOVE IN 1 DIRECTION

Vibrating source causes propagation of sound through some medium such as solid liquid gas. The distance the sound will travel depends on the medium, and the friction the medium will provide. Sound waves are propagated by a back-and-forth movement of molecules, which displaces the molecules in that medium

When sound travels through the air, the molecules closest to the vibrating object to move back-and-forth due to the elastic properties of the air molecules then you have the inertial elastic properties of the air molecules that cause pressure variations, which are known as condensation and rare fraction.

propagation is the act of the sound spreading

as sound propagates, it diminishes with intensity with an increased distance from the source of the sound

more friction and distance = quieter

sound travels fastest through water and most other solids than air

waveform example

terms

acoustics- study of physical properties of sound in the environment and how the sound waves travel

frequency (hz)-measure of sound for perception of pitch, shape of sound wave, high freq=shorter wavelength

amplitude (dB)-magnitude of sound, loudness,

phase- where the waveforms cycle of vibration begins

period(t/time)-amount of time it takes to complete one cycle

pure tones- examples of sound that hace one specific frequency and amplitude, this is what we are measuring when we assess peoples hearing

frequency and period have an inverse relationship, as f increases, p decreases, and vice versa

intensity- power distributed over an area, used to describe sound

pressure- force distributed over an area, used to describe sound

decibels

most common unit of measure for intensity, it is a logarithmic scale

0 dB does not mean the absence of sound, its a value of intensity which is a starting point for sound pressure with reference to human hearing

0 dB sound pressure level that will cause the eardrum to vibrate in the average adult

reference level= 0 db SPL

measured as a ratio between the sound pressure and a reference level

dB levels

dB IL-intensity level

dB SPL- sound pressure level

dB HL- hearing level

dB SL- sensation level (later)

wavelength

speed of sound over frequency, lower freq= larger wavelengths can move around objects easily

Periodic vs Aperiodic

periodic- waveform that repeats itself, fundamental frequency is the lowest frequency (has longest period) of the complex tone

Aperiodic- noise like a fricative

filtering

allowing some frequencies to pass through while others excluded, used in hearing aids

high pass- let high frequency pass through

low pass- let low frequency pass through

band pass- specific area let through

band reject- specific area not let through

Complex Waveforms

most everyday sounds are complex

case history

Key component of a successful hearing evaluation

observing the patient is an important part of the case history

hearing loss

congenital-born with vs acquired

tinnitus-ear ringing

vertigo-dizzy

otoscopy

prior to placing anything in ear

it is to detect collapsing canals

before insertion-examine pinna

insert, then…

ensure canals are not occluded with cerumen ot foreign objects

push on pinna and watch for collapsing canals

pull up and back on pinna to straighten canal

insert speculum into canal

very tip=speculum

hold otoscope like a pencil and bridge with the fingers against the side of patients face in order to prevent injury to the patient in case of movement

audiometry

audiometer- a medical device used to evaluate a person's hearing acuity and detect hearing loss

basic hearing test objective is to find hearing threshold

threshold is the lowest sound that a person can reliably respond to 50% of the time

test 250-8000 hz (pure tones)

describes degree of hearing loss

determines type of hearing loss

audiometers

audiometer- a medical device used to evaluate a person's hearing acuity and detect hearing loss

parts

frequency selector- change freq of tone

attenuator dial- change intensity of signal

transducer selector- how signals delivered

router switch- presents sound

interrupter switch- presents signal to patient

patient response indicator- light/sound saying patient responded

VU meter- monitor output level

transducers

device capable of vibrating when activated by electrical signal from the oscillator converting (transducing) electrical signals into vibrations that can be heard

there are 5 audiometry transducers

all are specifically calibrated to transmit equivalent sound pressure level to patient

types

insert earphones- insert fully

supra aural/TDH-bad for collapsing canal, higher output

high frequency (circum-aural)- high frequency tests

speakers-key to testing kids

bone oscillator-tells you type of hearing loss, delivers vibrations through skull to both ears, makes sure they are responding

air conduction (AC) vs bone conduction (BC)

headphones transmit sound via air conduction

bone conduction simulates the cochlea directly

testing both air conduction and bone conduction can determine cause of hearing loss

degree of hearing loss

Normal (Adult): 0-25

Normal (Child): 0-15

Slight (Child): 16-25

Mild: 26-40

Moderate: 41-55

Moderately Severe: 56-70

Severe: 71-90

Profound: 91+

 

Equations for Masking
Bone Conduction: TE AC-TE BC=     >10   ->Masking

Air Conduction: TE AC- NTE BC=    IA    -> Masking

hearing loss types

sensorineural

air and bone conduction scores will be similar

conductive

bone conduction is within normal limits, a gap between air conduction and bone conduction scores

mixed

combined conductive and sensorineural, bones scores outside of normal limits

testing

air conduction

250-8000Hz, octave frequencies

test interoctaves when there is a 20db difference between octaves

bone conduction

250-4000Hz, octave frequencies

when testing, anytime you get a response, go down 10db, until they stop responding, then go up 5db (down 10, up 5) repeat until 50% rate is obtained on ascending runs

testing types

standard- push button, raise hand

visual reinforcement activity- reward system

conditioned play audiometry- play a game

team testing- assistant helps in booth

tuning forks

quick way to determine asymmetrical or conductive vs sensorineural hearing loss but it is variable intensity range depending upon force and its not callibrated

Weber test

determines if affected ear has conductive or sensorineural hearing loss, helpful for unilateral hearing loss

stem is placed on midline of head, asks if patient hears it in middle of head or on one side or another

if hearing is normal or symmetrical SNHL (sensorineural hearing loss) should percieve midline, if percieves tone in normal hearing ear it is SNHL, if percieves tone in poorer ear it is CHL (conductive hearing loss)

Rinne test

tests air (AC) vs bone conduction (BC)

hold tuning fork at mastoid and then at auditory meatus, ask patient to report if sound is louder on the mastoid process or next to auricle

abnormal-negative, or when BC tone is percieved as louder than the AC tone

normal-positive, or when AC tone is heard louder than BC tone

wavelength- low frequency has longer wavelength

condensation-particles closer together, increased air pressure

rarefaction-particles spread out, decreased air pressure