Hearing Science Exam 2

Outer ear Helps

Funnel sound & localization

Parts of the Outer Ear

lobule

tragus

cavum concha

crus of helix

triangular fossa

helix

scaphoid fossa

superior crus of antihelix

inferior crus of antihelix

cymba concha

antihelix

EAM

antitragus

Ear canal

1/3 cartilage; makes ear wax

2/3 osseous: isthmus

Outer ear function

sound transmission

Middle ear protection

major resonator

sound localization

resonance & diffraction

Azimuth Estimation

determination of the direction of the horizontal plane

binaural

Elevation estimation

determination of the direction of the vertical plane

monaural

distance estimation

determination of how far we are away from a sound source

atresia

no ear canal

anotia

no pinna & ear canalM

Microtia

malformed pinna

cauliflower ear

swelling of pinna due to trauma

external otis

swimmers ear

infection

exostoses

bony growth on ear canal

Middle ear function

convert air based sound into mechanical energy into the inner ear

parts of inner ear

tympanic membrane

ossicles

eustachian tube

Tympanic membrane

lateral process manubrium (of mallues)

umbo

cone of light

pars tensa

pars flaccida

tympanosclerosis

scarring on the TM due to ear infection, tubes, ruptures

anatomy of ear canal

cartilaginous portion

bone portion

isthmus: narrow area where it moves from cartilage to bone

ear wax

open-closed tube amplifying sound: 2000-5000hz

Amplification of sound

8 dB

Sound movement

pinna (acoustical)

EAC

tympanic membrane (mechanical)

ossicles; malleus, incus, stapes

oval window (hydraulic)

scala vestibuli

basilar membrane

cochlear hair cells

IHC (electrical)

afferent neuron

auditory nerve

Azimuth Estimation

along horizontal plane

binaural

Elevation Estimation

Vertical plane

monaural

Distance estimation

how far we are from the sound source

includes sound intensity & amount of sound refelcted

2 localization cues

interaural time difference

interaural level difference

Interaural time difference

sound gets to one ear faster than the other, helps you know where the sound is coming from based on this timing

Interaural level difference

based on the shadow your head makes which affects the sound waves, some sounds will be louder to one ear than another

Monaural Cues

help us estimate the elevation (vertical plane) of incoming sound

reflected path vs direct path used to tell you how high a sound is coming from

Degree for best noise

45 degrees

2 main functions of outer ear

funnel sound/ sound transmission

localization

protection of the inner ear

Middle ear disorders

mastoiditis

cholesteatoma

mastoidectomy

otitis media

Mastoiditis

infection of mastoid hair cells

Cholesteatoma

tympanic membrane majorly contracted, problem w/ eustachian tube

• cyst with skin cells

  • non-cancerous growth of skin-like cells in the middle ear

Mastoidectomy

removal of mastoid air cells

Otitis Media

infection of middle ear

4 steps of middle ear infection

inflammation leading to the narrowing of eustachian tube

increase in neg pressure

mucus excretions lead to bacterial colonization

bacteria buildup & pus

inner ear hearing loss

Sensorineural

conductive

Sensorineural

through air and the outer/ middle earCo

Conductive hearing loss

bone conduction

presbycusis

• acoustic trauma, drugs, age, infection, congenital

impedance

moving from air-filled space to fluid causes an impedance mismatch of 4000

fixes of impedance

difference in surface area

ossicular lever

buckling effect

Differences in surface area

TM is larger than oval window, so force becomes more focused and thus more powerful

Ossicular lever

rotational motion at the incudomallear joint due to the ligaments attaching to malleus and the incus

increase force by 1.2dB or 1.5 times

Buckling effect

aka catenary lever

conical shape of the tympanic membrane means less movement with vibration and thus more force at the oval window

increase by 6 dB

Area Ratio : pressure transformer

increase energy by 17 fold

ratio of tympanic membrane area compared to the footplate of the stapes area

acoustic reflex

tensor tympani and stapedius will contract and stiffen the ossicular chain

basilar membrane

wider at apex

high frequencies resonate at base

sound enters scala vestibuli

sound waves within the cochlea are transverse

Modiolus

part of cochlea

bony axis of cochlea

osseous cavity where all spiral ganglion and nerve endings from the organ of corti join together to create the auditory nerve

provides structure for cochlea

Frequency

The basilar membrane is tonotopically organized, meaning there are areas that resonate with specific frequencies. The base of the membrane is more geared towards higher frequencies because it is stiffer and the apex is more geared to higher frequencies because it is less stiff.

Intensity

is processed by the outer hair cells, more energy and “loudness” is going to mean it is more intense.

Duration and timing:

how long the sound is and when the sound happens, the length of the vibration indicates how long the duration of the sound is.

IHC Shearing

shear away from modiolus towards longer stereocilia

• open ion gates where potassium comes in = depolarization

  • calcium opens side gates

OHC Shearing

shear against tectorial membrane

depolarization

when positive potassium ions enter the cell

• stereocilia are sheared away from the modiolus

Hyperpolarization

membrane potential of the cell becomes/ stays more negative

• stereocilia are sheared towards the modiolus

Type 1 Afferent Neurons

95%

covered in myelin and connected to IHC’s

20 type 1 afferent for each IHC

Type II

5%

thinner

not covered in myelin connected to OHC’s

attached to multiple outer hair cells

Spiral Ganglion

group of afferent neurons within modiolus

Endolymph

high in potassium

positive charge

scala media

Perilymph

high in sodium

positive charge

scala tympani / vestibuli

Fluid & depolarization

As the stereocilia shear, the potassium from the endolymph flows into the cell, causing a chain reaction that leads to action potentials – the electrochemical responses to sound

OHC depolarization

basilar membrane move up

tectorial membrane moves up

sterocilia get moved and ion gates open

potassium enters and depolarizes the cell

• sharpens frequency codes

• results in electromotility

Cochlear amplifier

depolarization of OHC (electromolity)

• It matters because less IHC will be stimulated (sharp), but the IHCs that are stimulated and stimulated more (tallness). Sounds are clear like we want them. 

• When the OHC’s are damaged, sounds are muffled.

Place Theory

frequency is coded by place stimulation along cochlea/ basilar membrane

physiologcial principle: based on stiffness and width of the basilar membrane

Each IHC & OHC tuned to a specific frequnecy

Characteristic frequnecy

each IHC & OHC is tuned to a specific frequency

blue line: normal functioning , 8,000hz

red: no response to frequency, impaired hearing. Takes a lot more dB to stimulate and loss of characteristic frequency, muffled speech

Temporal Theory

basic premise: frequency is coded by the frequency of nerve impulses generated by the incoming sound

Psychological Premise: all auditory neurons have a resting firing rate. the firing rate increases when IHC’s are excited and decreased when IHC’s are inhibited

can’t account for higher frequencies

Volley Principle

group of neurons that work together help hearing up to 5k Hz

• frequency is coded by the frequency of nerve impulses generated by the incoming sound

• individual auditory neurons can only fire up to 1000 Hz

• neuron groups work as teams to code higher frequency

Frequency Coding

Place theory + Temporal Theory

Intensity Cody

coded by number and type of activated neurons

Dynamic range

the intensity range between a neuron's threshold and saturation point. Most often between 24 and 40 dB.

Physiological principle

greater intensity = larger amplitude & broader traveling

this stimulates larger population of IHC and auditory neurons

3 types with different firing rates

(high spontaneous, mid spontaneous, low spontaneous)

Low Intensity = high spontaneous

High Intensity = Low spontaneous

Cochlear Implant

cochlear implant applies direct stimulation to the auditory nerve with electrical signals In

Intensity Coding

rate of electrode firing

Air

travels through outer/ middle/ inner ear to get to cochlea

50-60 dB better than bone conduction

Bone

vibrations of skull stimulate cochlea

bypass outer/ middle ear ; hearing

Bone conduction: own voice

• vibrations of skull from high pressure sounds produced when speaking that lead to hearing via bone conduction

Direct Vibrations: bone conduction

vibrations to skull that go straight to cochlea, mechanical energy directly to the cochlea

bone conduction: high intensity

difference with bone and air conduction, bone conduction is less efficient by 50-60 dB

conductive hearing loss: measure

seeing if the bone conduction ratings are better than the air conduction hearing test