Outer and Middle Ear Physiology

what are the physiological functions of outer ear?

•Protection

•Amplification

•Helps provide cues that will eventually be used to help us localize sounds

The outer ear protects ...

the tympanic membrane and the middle ear from physical damage and abuse

the pinna collects...

sound waves

the ear canal is a ...

resonator

The main resonance cavity of the ear is

the ear canal

We usually give a range of ________-________ Hz for the frequencies most amplified by this resonance in humans.

2000-3000 Hz

So, the pinna provides the acoustic cues we use for ________ in the sagittal plane

localization

Horizontal localization 2 mechanism:

Interaural level or intensity differences

Interaural time differences

What cues do you need 2 working ears for?

Binaural cues

Intensity differences between the ears result in ...

interaural level or intensity difference (ILD) cues

Timing differences between ears result in ...

interaural time difference (ITD) cues

the sound will arrive at a later phase at the farther earHorizontal localization

interaural phase differences (IPD)

Major benefit of middle ear:

impedance matching

This energy loss is compensated by middle ear through....

IMPEDANCE MATCHING.

Impedance matching mechanisms of the middle ear

1. Area transformer most important

2. Ossicular lever transformer

3. Curved membrane effect

Area transformer

Effective vibratory area oftympanic membrane(55mm2) is more than stapesoval window surface area(3.2mm2)

So, force produced by sound concentrated over small area

Ossicular Lever Transformer

The handle of Malleus 1.3 times longer than the Long process of Incus, providing Mechanical Leverage Advantage.

So, Ossicles increases force of movement by 1.3 times.

Curved Membrane Effect

Movement of the Tympanic membrane more at the Periphery than at Center where Malleus is attached.

A buckling motion of tympanic membrane increases force by a factor of 2:1

Area Transformer pressure ratio

17:1 (24.6 dB)

Ossicular lever transformer pressure ratio

1.3 :1 (2.3 dB)

Curved membrane effect pressure ratio

2:1 (6 dB)

Total advantage ratio=

approx. 44.2:1 at 1000 Hz Equivalent to about 33 dB24

The middle ear impedance matching mechanisms result in an increase in sound pressure of ___ dB

33 dB

pressure loss from the outer to inner ear is?

35-40 dB

The outer ear resonances, middle ear impedance matching, and some other factors work together to most effectively transmit sounds between about

500 and 6000 Hz.