PSYC10003 Lecture 8: PSYC10003 8. The Auditory and Somatosensory Systems
8. The Auditory and Somatosensory Systems
Changes in Air Pressure from Sound Waves
• Sense of hearing (audition) is vital for many aspects of life
• Serves as eal aig sste he vision not available
• also underlies ability to communicated using spoken language
• hear sounds when objects vibrate,
causing air molecules to compress and rarefy (become more dispersed)
leading to waves that travel away from object at around 1,100 km/h
• frequency of vibration measured in cycles per second (Hertz, Hz)
• humans can perceive sounds in range 30 – 20,000 Hz
Physical and Perceptual dimensions of sound waves
• loudness determined by the
degree to which air molecules are
pushed together and pulled apart;
more vigorous vibrations of an
object can cause larger amplitude
waves, creating more instese
sounds
• pitch is determined by frequency
of sound waves produced by
vibrating object; the more sound
waves per second the higher
pitched the sound
• timbre (soud ualit deteied opleit of soud aes, the oe little peaks ad toughs
in the waveform the more complex the sound. A completely smooth sinusoidal waveform is a pure
tone
Structure of the human ear
• outer ear: consists of outer fleshy pinna,
auditory canal, and tympanic membrane
(eardrum)
• tympanic membrane vibrates with
soundwaves that enter auditory canal and
signal transmitted to inner hear
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2
Middle and Inner ear
• middle ear:
o consists of three tiny bones
o ossicles, malleus (hammer) is connected to
tympanic membrane
o transmits vibrations via incus (anvil) to the
stapes (stirrup
▪ connected to a structure called
cochlea (snail) which is part of the
inner ear
• inner ear: consists of the cochlea, which contains
receptors for analysing sounds
o bony structure
o has two small membranes that form
windows on its fluid-filled interior
o stapes is connected to oval window, sound
waves that case stapes to move in and out move fluid over receptors inside cochlea.
o Because the cochlea is a closed structure, another membrane is needed to allow fluid to
move: this membrane is the round window
Basilar Membrane
• Cochlea derives name from snail-like shape
• Scanning electron micrograph shows cochlea with bony roof cut away
• Coloured ribbon added to illustrate position and shape of sheet tissue
containing auditory receptors
o Sheet of tissue: basilar membrane
The Cochlea
• Basilar membrane sits in the centre of cochlea
• Runs all the way from its base to its apex (top)
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3
Organ of Corti
• Cross-section taken across longitudinal axis of cochlea reveals three inner chambers, each fluid-filled
• On floor of centre chamber is structure called Organ of Corti
o Runs all the way along length of cochlea
o Composed of basilar membrane at base
o Receptors in middle called hair cells (inner and outer
o Rigid shelf over top: tectorial membrane (tectum means roof)
Hair cells and stereocilia
• on top of hair cells are tiny filaments: stereocilia
• sound waves cause basilar membrane to move relative to tectorial membrane above it
• bends stereocilia either by direct contact with tectorial membrane (In case of outer hair cells) or by
fluid motion induced by movement of basilar membrane
• bending of stereocilia of hair cells produces receptor potentials that convert soundwaves into neural
signals
basilar membrane
tectorial membrane
outer hair cells
inner hair cell
outer hair cell
stereocilia
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Document Summary
Serves as (cid:862)ea(cid:396)l(cid:455) (cid:449)a(cid:396)(cid:374)i(cid:374)g s(cid:455)ste(cid:373)(cid:863) (cid:449)he(cid:374) vision not available: sense of hearing (audition) is vital for many aspects of life, also underlies ability to communicated using spoken language, hear sounds when objects vibrate, Causing air molecules to compress and rarefy (become more dispersed) Leading to waves that travel away from object at around 1,100 km/h frequency of vibration measured in cycles per second (hertz, hz: humans can perceive sounds in range 30 20,000 hz. A completely smooth sinusoidal waveform is a pure tone. Structure of the human ear: outer ear: consists of outer fleshy pinna, auditory canal, and tympanic membrane (eardrum) membrane with tympanic soundwaves that enter auditory canal and signal transmitted to inner hear vibrates. Basilar membrane: cochlea derives name from snail-like shape, scanning electron micrograph shows cochlea with bony roof cut away, coloured ribbon added to illustrate position and shape of sheet tissue containing auditory receptors, sheet of tissue: basilar membrane.
