outer ear

4 portions of temporal bone

squamous

mastoid

tympanic

petrols

squamous portin

forms lateral, anterior, and upper part

zygomatic process

fan, goes above and around ear

petrous portion

one of densest bones body

located at base of skull

encase hearing and balance organs

mastoid and tympanic portion

fused

contributes to formation of tympanic cavity and EAM

mastoid has air cells

sphenoid bone

complex

at base of skull

contains sphenoid sinuses

inferior side grooved for ET

Where does the ear lie in the skull from a horizontal view?

Inner ear more posterior and angled slightly backwards

Parts of outer ear

Auricle/ pinna

External auditory meatus ( ear canal(

What is the first place we start collecting sound?

Outer ear

Describe the pinna

Most obvious portion of ear

Composed of flexible cartilage and skin

Internal same shape as external structure

External auditory canal

Tube like

2.5-3 cm long

0.75 diameter

Outer 1/3- ½ cartilage

1/2-2/3 bone

S shaped path

4 functions of outer ear

Protection

Maintenance

Sound amplification

Sound localization

Protection

Fragile middle and inner ear structures less accessible

Outer 1/3-1/2 has hair and glands

Objects have harder time reaching TM

Cerumen

Hairs of outer ear

Catch microbes before they can enter ear canal

Gets thicker and darker as we age

Cerumen

Sebaceous glands produce sebum

Lubricate canal

Repel water

Contains anti-microbial properties and a PH level

Odor discourages insects

Self maintenance

Skin that covers ear canal migrates out

New cells generated at/near umbo no the TM

Skin migration transports the cerumen out of the eat

Cerumen traps dust, particles, and other debris

Nerves in EAM

Receptors for pain and sensitivity

V: trigeminal

VII: facial

IX: glossopharyngeal

X: vagus

Transfer function

Combination of the amplitude and phase spectra that describe sound pressure changes due to the intervening structures

Head related transfer functions (HRTDS)

Transfer functions describing changes between the source and outer ear

Resonance

Property of a. System/ structure at a particular frequency with minimum disposition/ reduction of energy

Resonant frequency

Frequency at which resonance exists

Resonance of pinna

5k Hz

Resonance of whole outer ear

2K- 5k Hz

Resonance of EAM

2700 Hz

Concha

5500 Hz

How does the pinna amplify sound

Passive sound amplifier

Gathers and channels sound towards ear canal

Complex resonator for high frequency sounds due to the configuration of the ridges and depression on the surface of it

How does the ear canal amplify sound

Tube closed at one end

Resonate the sound with wavelength 4 times the length of tube

Resonant peak occurs at about 2.850-3.4 KHZ

Sound level gain due to outer ear about 10-15 dB

Most gain from outer ear at what?

5k Hz

Other contributions to transfer function

Sound pressure level (SPL) at the TM is also affected by the head, neck, and torso

Effect of head, neck, and torso will create a difference in SPL at each ear when a sound is not in the medial plane

Sound localization

The ability to accurately determine the location of a sound source

3 spatial dimensions a sound source can be localized

Horizontal plane

Vertical plane

Distance

How does the anatomy of the pinna contribute to localization of sound in horizontal and vertical planes

Depressions and ridges of pinna reflect the sound forming different spectra cues

Depressions resonate sounds contributing to different HRTFS

Vertical plane relies on spectra cues

Horizontal plane relies on spectra and other cues

Pinna notch

Shifts about 5-1.1 KHZ

Notch at about 6 KHZ for below sound source

Notch gets higher frequency as the sound source moves upward

Lower frequencies most parallel

Other contributions to sound localization

Relative position of a sound source to the listener affects HRTF

Binaural cues for horizontal plane localization

3 basic cues of sound

Interaural differences in time

Interaural differences in intensity

Monaural spectrum shape