Hearing 164-170

Our auditory sense

Frequency the number of complete wavelengths that pass through point at a

given time. This determines the pitch of a sound.

Amplitude is how loud the sound is. The higher the crest of the wave is the louder the sound is. It is measured in decibels.

The Ear

The Path of Sound

• Outer Ear = collects sound waves• Middle Ear = amplifies• Inner Ear = Transduction happens

Outer Ear

Sound wave comes into ear and…• Pinna – helps pinpoint

location of sound• Ear canal → eardrum =

tightly stretched– membrane that vibrates

when sound hits it

Middle Ear

• The eardrum vibrates and then…– Ossicle bones = hammer,

anvil, stirrup amplify vibration

– Oval window = another membrane to inner ear

Inner Ear

• Cochlea = fluid-filled, snail shaped tube. Vibrations cause movement in fluid

• Basilar Membrane – hair cells on floor of cochlea. Bending of them stimulates the auditory nerve cells

Transduction in the ear• Sound waves hit the eardrum anvil

hammerstirrupoval window.• Everything is just vibrating.• Then the cochlea vibrates.• The cochlea is lined with mucus

called basilar membrane.• In basilar membrane there are hair

cells.• When hair cells vibrate they turn

vibrations into neural impulses which are called organ of Corti.

• Sent then to thalamus up auditory nerve.

It is all about the vibrations!!!

Pitch Theories

Place Theory and Frequency Theory

Helmholtz’s Place Theory

• Different hairs vibrate in the cochlea according to different pitches.

• So some hairs vibrate when they hear high and other vibrate when they hear low pitches.

Frequency Theory

• All the hairs vibrate but at different speeds.

• But this theory has trouble explaining high pitch sounds because our hairs cannot vibrate at certain speeds.

DeafnessConduction Deafness

• Something goes wrong with the sound and the vibration on the way to the cochlea.

• You can replace the bones or get a hearing aid to help.

Nerve (sensorineural) Deafness

• The hair cells in the cochlea get damaged.

• Loud noises can cause this type of deafness.

• NO WAY to replace the hairs.

• Cochlea implant is possible.