Auditory system

outer ear parts

pinna

external auditory canal

tympanic membrane (ear drum)

middle ear parts

tympanic membrane (ear drum)

ossicles

peripheral auditory system

• outer ear

• middle ear

• inner ear

• auditory nerve

central auditory system

brain

function of peripheral auditory system

conduction and transduction/encoding

function of central auditory system

transmission and decoding/ perception

tympanic membrane

transition between the outer and middle ear

lateral (outer) layer of TM

skin lining the ear canal

middle layer of TM

fibrous — TM stiffness

medial (inner) layer

mucous lining in middle ear

conduction (outer ear function)

• Pinna collects sound from the environment

and funnels it into the ear canal

• Ear canal channels sound towards the

tympanic membrane

resonance (outer ear function)

• ear canal = closed tube

occlusion effect

closing ear canal —> Sound gets trapped in the ear resulting in the sound resonating at a different frequency (lower pitch)

protection (outer ear function)

s- shaped curve

½ has hair

ear wax —> keeps things (dust and particles) out of ear

localization (outer ear function)

The ability to locate where the sound source is located (where the sound is coming from)

Inter-aural Level Difference (ILD) Cues

• The brain compares amplitudes of a sound between the two ears

• head blocks the sound heading to the opposite ear (softer in other ear)

• Primarily a result of the head shadow effect

• High frequencies

Inter-aural Timing Difference (ITD) Cues

• The brain compares phase difference of a sound between the two ears

• It takes longer for the sound to arrive at the opposite ear

• Determined by the distance between the two ears

• Low frequencies

the middle ear is an…

air filled cavity

ossicles

malleus, incus, stapes

eustachain tube

Tube connecting the middle ear to the throat

◦ Keeps air pressure between middle and outer

ears relatively equal

◦ Normally closed, opens to allow air in or out of

the middle ear cavity

◦ Allow fluid to drain out of middle ear cavity

energy transformation (middle ear function)

acoustic energy —> mechanical energy

impendance matching

different mediums have different impedances ( opposition to the flow of energy)

the middle ear amplifies sound using the

◦ Area ratio difference

◦ Lever action

◦ Bucking effect

area ratio

Sound pressure collected on TM (large surface area) is concentrated onto oval window (small

surface area)

lever action

action of malleus causes increased displacement at the stapes

buckling effect

The eardrum is not flat, it is slightly conically shaped —> causes a doubling of force results in n amplification

acoustics reflex

Contraction of muscles in the middle ear that

hold the ossicles in place in response to loud

sounds

◦ Stapedius muscle

◦ Tensor tympani

conductive hearing loss

Hearing loss resulting from sound being unable make it through the outer and/or middle ear

Cerumen impaction hearing loss

a buildup of earwax (cerumen) that blocks the ear canal or presses against the eardrum

Microtia or atresia hearing loss

congenital (present at birth) conditions that affect the outer and middle ear

Tympanic membrane perforation

a hole or tear in the thin, cone-shaped tissue (tympanic membrane) that separates your ear canal from your middle ear

Ossicular disarticulation hearing loss

the separation or disruption of the tiny bones in the middle ear