Audiology Week 3

What are the 3 sections of the ear and their corresponding function?

Outer ear: collects soundwaves from the environment

Middle ear: transmits sounds collected from the outer ear to inner

Inner ear: the sensory organ for hearing and balance

What is the outer ear referred to?

pinna or auricle

What is the actual opening of the ear called

external auditory canal or ear canal

another name you might see for this is the external auditory meatus

What is the main function of the external ear

act like a funnel to direct sound into the ear canal

the grooves help with vertical sound location

How long is the ear canal in adults

2.5 cm long

How many portions of the ear canal are there and what are they

outer 1/3 is the cartilaginous portion made of softer flexible cartilage

• has small hairs and cerumen (ear wax) to keep material out

Inner 2/3 is the osseous portion that is made of hard bone

What is the shape of the ear canal

an s shape

How does sound amplification work with the ear

the folds in the pinna reflect sound into the ear

this boosts certain frequencies (called gain)

the outer ear boosts high frequencies from 3-7 kHz

the ear canal acts like a resonance tube (this boosts frequencies from 2-4 kHz)

What is sound localization

your ears help you determine where sounds are in space

monaural (one ear) cues help with estimating location on the vertical plane

binaural (two ears) cues help with estimating location on horizontal plane

these are called interaural (between ears) differences

What is the middle ear

the middle ear is an air-filled space that starts at the tympanic membrane and ends at the bony wall that separates the middle ear from the inner ear

the middle ear contains the three smallest bones in the body

main function: transmitting the vibrations of the ear drum to the inner ear

• turn pressure fluctuations to physical vibrations

What is the temporal bone

the middle ear space is located within the temporal bone

very thick bone

connected to the skull and attaches to the jaw

many cranial nerves pass over the temporal bone

What is the tympanic membrane

the tympanic membrane (eardrum or TM) is a small cone-shaped membrane

the membrane consists of two parts:

• the pars tensa which is stretched (taut)

• the pars flaccida which is relatively loose (flaccid)

the TM is the boundary to the middle ear

it converts acoustic vibrations (sound waves) into mechanical vibrations

about the size of a pencil eraser

What is otoscopy

otoscopy means looking into the ear

used to observe the ear canal and the tympanic membrane

a healthy TM is clear-ish and reflects light

can sometime see the bones of the middle ear behind it

Middle ear anatomy

the middle ear houses the ossicles- the middle ear bones

malleus, incus, stapes

What holds the ossicles in place

two important muscles are the tensor tympani and stapedius

acoustic reflex: these muscles contract in response to loud sounds as a protective mechanism

stiffens the middle ear system and reduces high-frequency sound transmission

What is the eustachian tube

thin tube that connects the middle ear space to the back of the throat (nasopharynx)

equalizes pressure in the middle ear (popping your ears)

also helps drain any fluid that might accumulate in the middle ear space

What is different about a kid’s eustachian tube

infants’ tube is flat (gravity will push more stuff out in adults)

big reason why kids get ear infections

What is tympanometry

diagnostic tool that tests the movement of the middle ear (mostly ear drum and malleus)

can determine normal function or a range of other issues:

• fluid in the ear

• perforation (holes in the ear drum)

• hypermobility/stiffness

What is the middle ear function

purpose is to transfer acoustic energy (sound pressure fluctuations) into mechanical energy (vibrations) that are sent to the inner ear

air → tissue/bones → fluid

impedance= resistance

middle ear acts as an impedance matcher

What are the two main middle ear mechanisms to overcome the impedance mismatch

the area ration pressure transformer

the ossicular lever

What is the area ratio pressure transformer

most effective mechanism of the middle ear: area ratio pressure transformer

think of a high heel

high heels hurt more when getting stepped on because there is more pressure on a small spot (same thing in ear)

the TM is about 1.7 times larger than the oval window, this ration works as a pressure amplifier

amplifies the force by about 25 dB

What is the ossicular lever

the length of the malleus is greater than the length of the incus

• this creates an anatomical lever

• this increases the pressure by about 3 dB

can put more pressure on the other side with less effort