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Sound And The Structure Of The Auditory System Notes

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This is an extract of our Sound And The Structure Of The Auditory System document, which we sell as part of our Neurology Notes collection written by the top tier of Bristol University students.

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Lecture 35, 38 & 40 Sound and Structure of the Auditory System




Properties and perception of sound o Amplitude or 'loudness' (dB) o Frequency or 'pitch' (Hz) Conductive pathway for sound o Conductive- outer ear
? External auditory canal
? Tympanic membrane (eardrum) o Middle ear
? Malleus; Incus; Stapes (in the oval window)
? Round window (covered by secondary tympanic membrane) o Sensory-Inner ear
? Semicircular canal (vestibular branch of VIII)
? Cochlea (cochlea branch of VIII)
? Auditory tube The ear- structure and function o Middle ear function- impedance matching
? More energy required to move fluid than air
? Ossicles have lever action
? Eardrum to round window surface area= 20:1 in humans
? Results in 20x pressure, enough to move fluid
? Without impedance matching only 0.1% energy transfer o Middle ear- ossicular reflex
? Protective reflex against loud sounds (>70dB)
? Stiffens lever reducing energy conduction (done by tensor tympani muscle & stapes muscle)
? No role above 1 or 2kHz in man
? Helps discrimination where lots of low freq. Noise
? Ineffective for impulse noise (50-100ms delay) o Inner ear
? 1, 7 & 8= Vestibular system (semi-circular canals)
? 10= Oval window moved by ossicles
? 11= Round window
? 13= Cochlea
? 5= Basilar membrane inside cochlea o Cochlea
? Spiral structure
? Fluid filled, compartmentalised

Cochlear fluids

* Perilymph o Resembles CSF o Bathes cell bodies of organ of Corti o K 7mM; Na 140mM; 0mV potential

* Endolymph o Resembles ICF o Sealed in tight compartment o Bathes surface of organ of Conti o Maintained by stria vascularis o K 145mM; Na 1mM; +80mV potential
? In mammals, organ of Corti=organ of hearing

* Located on flexible basilar membrane

* Inner & outer hair cells- sensory

* Spiral ganglion nerve cells

* Associated with supporting and non-sensory cells

* Hair cells held rigidly The specialist hair cells o Hair cells- sound to nerve impulse
? Inner (IHCs- 3,500)) and Outer (OHCs- 12,000) hair cells
? Afferent & efferent connections
? Sensitive to damage and disease (not replaced in mammals)
? Mechano-electrical transduction o The sensory hair cells*Stereocilia (hair bundle)

* Mechanosensing organelles of hair cells


Respond to fluid motion for various functions (hearing and balance)

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