Darkthorn’s Blog

Sound is a wave of pressure travelling through an elastic medium by mechanical disturbance of the molecules of the medium.

External ear – pinna and other appendages

- funnels sound into ear canal and modifies the sound

Middle ear – tympanum (eardrum), mallus/incus/stapes and Eustachian tube

- optimizes delivery of air-born sounds energy

o ossicles act as a lever to amplify sound

o complex tympanum vibrations

Inner ear – coiled, fluid-filled tube, completely encased in bone except for two membrane covered openings.

- Sound energy transduced into action potentials

- Vestibular and basilar (cochlear partition that contains the organ of corti) membranes

o Haircells possessing steriocilia (contain ion channels) are covered by tectorial membrane (jelly-like)

Transduction

1. Vibration of stapes footplate against oval window causing vibration of cochlear contents

2. Vibration of the cochlear partition increases in size, reaches a peak, then rapidly declines

3. Some ion channels in the steriocillia are open

4. Vibration of cochlear partition moves steriocillia, causing cyclic opening/closing of ion channels

5. Receptor membrane potential is affected by hair cells all opening/closing

Transmission

1. Deoplarisation causes transmitter release to underlying afferent nerve and produces action potentials

2. Opening channels (with sound) increases numbers of action potentials

3. Cochlear vibration at each point corresponds to a different frequency (therefore different nerve fibres)

4. Damage to OHC’s causes hearing loss due to less sensitivity

Sound à accessory structures à vibration of cochlear position à displacement of steriocillia

outer hair cells contract opening of more ion channels

brain modulation of action potentials modulation of transmitter release depolarisation