The Outer, Middle, & Inner Ear

outer, inner, middle

sections of the ear

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

external auditory canal (ear canal)

opening of the ear

pinna

the part of the ear that sticks out from your head

funnel

the main function of the external ear is to act like a _______ to direct sound into the ear canal

→ it’s similar to cupping your hand up to your ear - sound gets louder when you do that because you’re directing more of the sound waves into the canal

head and torso amplification

• sounds reaching a listener are affected by the body, head, and outer ear

• several pinna cavities have resonance (sound enhancing) effects

• each anatomical feature amplifies sounds at certain frequencies

directionality of the outer ear

the angle that sound approaches the ear has an effect on how much it is amplified AND in what frequency ranges

directionality

determining where a sound comes from in space involves localization and spatial orientation

localization

azimuth estimation

process of determining the direction on the horizontal plane

elevation estimation

process of determining the direction of the vertical plane (sounds from above and below)

spatial orientation

localization

distance estimation

process of determining how far we are from a sound source

monaural localization cues

• the localization cues created by reflection and refraction of sound by the folds, cavities, and ridges of each outer ear

• primary cues for estimating elevation

• when a sound wave reaches the pinna, some of the original sound wave goes straight in the ear canal, and some of it gets reflected around by the pinna and “bounced” into the ear

• think of a coin going around the swirly machine things at the mall

interaural (between ear)

just like your brain compares the spectrum of reflected sounds from one ear to help determine elevation, it can use _______ to help determine the location of sound in the horizontal plane

interaural intensity differences

intensity differences between the ears result in ______ ______ _____ (IID) cues

→ sound arriving from the left side will be louder in the left ear

interaural time difference

timing differences between ears results in ______ ___ _____ (ITD) cues

→ sound arriving from the left will be earlier in the left ear

→ another term for this is interaural phase difference (IPD) cues

ear canal

• roughly 2.5 cm long

• usually in diagrams it looks like a straight tube, but they’re usually curvy like an S-shape

• has cartilaginous portion and osseous, the bony portion

tympanic membrane

the ear canal is basically like an open/closed tube: open at the meatus and closed at the TM

middle ear structures

• tympanic membrane

• ossicles

• muscles

• nerves

• eustachian tube

tympanic membrane

• also called the eardrum

• slightly cone-shaped membrane

• tip is called the umbo

annulus

ring shaped ligament that holds the tympanic membrane in place

pars tensa

stretched (taut) part of the tympanic membrane

pars flaccida

loose (flaccid) part of the tympanic membrane

cone of light

a reflection of the light you’re using to look into the ear

otoscopy

• the act of looking into the ear canal to observe the TM

• device used = otoscope

left ear

if pac-man is facing the left or it’s 7:55, you are looking at the ____ ____

right ear

if pac-man is facing the right or it’s 5:05, you are looking at the ____ ___

tympanic cavity

the middle ear space, occupies 2 cm³ of space

ossicles

the middle ear bones

→ malleus

→ incus

→ stapes

stapes

1

incus

2

malleus

3

tegmen tympani

top plate of the cavity & has a thin layer of bone that separates the middle ear space from the brain cavity

aditus ad antrum

hole in the top, which leads to a space in the mastoid portion of the temporal bone

mastoid air cells

the antrum is a small chamber in the mastoid portion of the temporal bone and is surrounded by ______ ___ _____

manubrium

the _______ of the malleus attaches to the tympanic membrane

annular ligament

the stapes footplate is held in the oval window by a ring-shaped ligament called the ______ ______

anterior ligament of the malleus

the anterior process of the malleus is attached to the anterior wall of the tympanic cavity by the ______ ______ __ ___ ______

posterior ligament of the incus

the posterior process of the incus is attached to the _____ ______ __ ___ ______

tensor tympani

• middle ear muscle

• innervated by CN V

• connects to malleus

stapedius

• middle ear muscle

• innervated by CN VII

• connects to the stapes

tense up, prevent damage

what do the stapedius and tensor tympani do when you hear really loud sounds? what do they do this?

eustachian tube

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

eustachian tube purposes

1. equalizes pressure in the middle ear

2. drain any fluid that might accumulate in the middle ear space

children

have much shorter and flat eustachian tubes, making them more susceptible to ear infections

otitis media

happens when eustachian tube gets blocked, inflammation of the middle ear

valsava maneuver

one way to try to open the eustachian tube

middle ear physiology

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

transducer, impedance matching device

the middle ear acts as a ________ and an ________ _______ ______

area ratio, lever, buckling

the middle ear pressure transformer has three mechanisms:

• the ___ ____ pressure transformer

• the ossicular _____

• the catenary lever (_____ effect)

area ratio pressure transformer

• the most effective mechanism of the middle ear

• the size of the TM is 17 times larger than the stapes footplate / oval window

• this means that the pressure at the oval window is about 17 times (about 25 dB) greater than the pressure at the tympanic membrane

ossicular lever and catenary lever (bucking effect)

• because the length of the malleus is greater than the length of the incus, an anatomic lever is created

• this means that the pressure at the incus is about 1.15 times (about 1.2 dB) greater than the pressure at the malleus

• because the umbo is displaced less than the rest of the tympanic membrane, an anatomic lever is created

• this means that the pressure at the umbo is about two times (6 dB) greater than the pressure across the entire membrane

32 dB

combining the effects of all these mechanisms:

17 × 1.15 × 2 = 40

so, 40 times increased sound pressure at the stapes footplate, which results in roughly __ ___

250 and 6000 hz

together, the outer ear resonances and middle ear impedance matching work together to effectively transmits sounds between about ____ ___ _____ __

oval window

footplate of stapes is attached to the ____ _____

perilymph

• fills the scala vestibuli and scala tympani

• higher sodium concentration (K+)

endolymph

• fills the scala media

• higher potassium concentration (Na)

cochlea ‘unrolled’

• basilar membrane

• scala tympani

• scala vestibuli

• helicotrema

• oval & round windows

• endolymph vs. perilymph

apex

what part of the cochlea responds better to low frequencies?

base

what part of the cochlea responds better to high frequencies?

high frequency

because sound always goes high to low, these hairs are the most susceptible

analogy: if there was one door that allowed entrance, its path would become worn

organ of corti

• houses hair cells

• turns travelling waves into nerve impulses

embedded

outer hair cell stereocilia are ________

not embedded

inner hair stereocilia are ___ ________

afferent, efferent

______ neurons transmit sensory information from hair cells to the brain, while _____ neurons project from the brain back to the hair cells, primarily modulating their function

sensorineural hearing loss

• difficulty hearing due to damage in the inner ear (cochlea) or the auditory nerve, leading to difficulty perceiving or transmitting sound signals

• cochlea is affected, so bone & air conduction are both impacted, and gap is very small

conductive hearing loss

• occurs due to problems in the outer or middle ear, preventing sound waves from reaching the inner ear

• can be caused by infection, accident

• presents normal bone conduction thresholds

ICF

model that measures the implication hearing loss will have on various individuals

balance organs

we have 5 - or 10 total

3 canals

2 otolith organs

semicircular canals

• superior, posterior, and horizontal

• houses hair cells

• translates head movements into nerve impulses

otolith organs

• utricle, saccule

• maintain balance when moving head

• house otoconia

• responsible for forward & backward motion & up/down motion