Chapter 7: Audition
Light: Does not require a medium to travel ear, when sound energy contacts the eardrum, the alternating
● Transverse Wave: Vibrates perpendicular to direction it's compression (by a band of compressed air molecules) and
travelling in decompression of air (by a band of less dense air molecules)
Sound: Requires a medium to travel causes the membrane to vibrate
● Mediums of sound include: air, liquids and solids (sound The Middle Ear: Medial structure of the ear, after the outer ear and
travels faster in liquids and solids than gases due to their before the inner ear
relative compactness) ● The Ossicles: Three small bones (smallest in the body),
● Outer space = a vacuum (no matter = no pressure = no connected to the tympanic membrane, named according to
sound) their shape: the hammer, anvil and stirrup, the vibrations
● Sound waves = initiated by a vibration which causes the air from the eardrum resonate/vibrate, into these bones,
molecules surrounding the source of the sound to move, amplifying the sound as it transfers into the inner ear
causing a chain reaction of moving air particles The Inner Ear: The final structure of the ear before neural conduction
● Longitudinal Wave: Vibrates parallel to direction it's ● The Cochlea: A fluid-filled tube in the inner ear, coiled to
travelling in minimize the space it takes up, looks like a conch shell,
● Humans can perceive sounds that lie anywhere between 20 about 35 mm long, contains neural tissue to transfer the
and 20,000 Hz changes in fluid to neural impulses, the stirrup resonates
sound through a small hole called the oval window (20
times smaller than the ossicles, separates inner from middle
ear) at its base, when the stirrup pushes in, it displaces the
cochlear fluid which bulges out of a second opening at the
base of the cochlea: the round window, when the stirrup
retracts, allowing space for the fluid again, the fluid at the
round window retracts as well, alternating bulging and
retracting occurs at the frequency of the sound wave
○ The Basilar Membrane: Stiff structure in the
cochlea, runs the length of the cochlea like a
carpet, innervated with hair cells, vibrates at diff
points along its length according to specific
frequencies, base = near, apex = far
■ When the oval window is pushed
inward, waves in the fluid inside the
cochlea push the basilar membrane
downward
■ When the oval window is pushed
Amplitude: Height of a wave outward, fluid forces the basilar
● Loudness in sound waves, brightness in light waves membrane upwards
● Measured using a logarithmic scale of decibels (dB) ■ Has Tonotopic Organization:
● The perceived loudness of a sound doubles for every 10 Organization in the auditory pathway,
decibel increase on a single dimension corresponding to
Wavelength: Distance between two successive peaks/ two successive the pitch of sound
troughs ■ Lower frequency = resonates close to
● Pitch/tone/note in sound waves, hue in light waves the apex (which is wide/thin)
○ Small wavelength = high pitch = high frequency ■ Higher frequency = resonates closer to
○ Large wavelength = low pitch = low frequency the base (which is narrow/thick)
● Measured in Hertz (represents the number of cycles per ■ All frequencies within the human
second) audible range have specific
Purity: The distinctive sound that results from constructive and corresponding locations along the
destructive interference of sound waves, perceived complexity of basilar membrane
sound ■ Longer basilar membrane = allows
● Timbre in sound waves, saturation in light waves processing of a wider range of
● This phenomenon explains why diff instruments, despite frequencies
playing the same note, sound unique ○ Organ of Corti: Houses the hair cells which
The Pathway Inside the Ear: become displaced by vibrations in the basilar
The External/Outer Ear: Where our auditory system collects sound, membrane, causing them to convert the frequency
initial structure of the ear of the sound into an electrical signal
● The Pinna: The cone-shaped protuberances on the side of ■ Mechanical displacement of the hair
your head (what most people colloquially refer to as their cells allows positive ions from the
ear), acts like a satellite disk, directing sound waves into the extracellular fluid to enter the body of
ear canal the cell
● Ear Canal: Narrows as it moves towards the eardrum, ■ The loudness of the sound affects the
amplifies sound waves extent to which the hair cell bends + the
● Tympanic Membrane/ Eardrum: Thin membrane forming number of positive ions entering the cell
the back wall of the ear canal, separates outer and middle
Light: Does not require a medium to travel ear, when sound energy contacts the eardrum, the alternating
● Transverse Wave: Vibrates perpendicular to direction it's compression (by a band of compressed air molecules) and
travelling in decompression of air (by a band of less dense air molecules)
Sound: Requires a medium to travel causes the membrane to vibrate
● Mediums of sound include: air, liquids and solids (sound The Middle Ear: Medial structure of the ear, after the outer ear and
travels faster in liquids and solids than gases due to their before the inner ear
relative compactness) ● The Ossicles: Three small bones (smallest in the body),
● Outer space = a vacuum (no matter = no pressure = no connected to the tympanic membrane, named according to
sound) their shape: the hammer, anvil and stirrup, the vibrations
● Sound waves = initiated by a vibration which causes the air from the eardrum resonate/vibrate, into these bones,
molecules surrounding the source of the sound to move, amplifying the sound as it transfers into the inner ear
causing a chain reaction of moving air particles The Inner Ear: The final structure of the ear before neural conduction
● Longitudinal Wave: Vibrates parallel to direction it's ● The Cochlea: A fluid-filled tube in the inner ear, coiled to
travelling in minimize the space it takes up, looks like a conch shell,
● Humans can perceive sounds that lie anywhere between 20 about 35 mm long, contains neural tissue to transfer the
and 20,000 Hz changes in fluid to neural impulses, the stirrup resonates
sound through a small hole called the oval window (20
times smaller than the ossicles, separates inner from middle
ear) at its base, when the stirrup pushes in, it displaces the
cochlear fluid which bulges out of a second opening at the
base of the cochlea: the round window, when the stirrup
retracts, allowing space for the fluid again, the fluid at the
round window retracts as well, alternating bulging and
retracting occurs at the frequency of the sound wave
○ The Basilar Membrane: Stiff structure in the
cochlea, runs the length of the cochlea like a
carpet, innervated with hair cells, vibrates at diff
points along its length according to specific
frequencies, base = near, apex = far
■ When the oval window is pushed
inward, waves in the fluid inside the
cochlea push the basilar membrane
downward
■ When the oval window is pushed
Amplitude: Height of a wave outward, fluid forces the basilar
● Loudness in sound waves, brightness in light waves membrane upwards
● Measured using a logarithmic scale of decibels (dB) ■ Has Tonotopic Organization:
● The perceived loudness of a sound doubles for every 10 Organization in the auditory pathway,
decibel increase on a single dimension corresponding to
Wavelength: Distance between two successive peaks/ two successive the pitch of sound
troughs ■ Lower frequency = resonates close to
● Pitch/tone/note in sound waves, hue in light waves the apex (which is wide/thin)
○ Small wavelength = high pitch = high frequency ■ Higher frequency = resonates closer to
○ Large wavelength = low pitch = low frequency the base (which is narrow/thick)
● Measured in Hertz (represents the number of cycles per ■ All frequencies within the human
second) audible range have specific
Purity: The distinctive sound that results from constructive and corresponding locations along the
destructive interference of sound waves, perceived complexity of basilar membrane
sound ■ Longer basilar membrane = allows
● Timbre in sound waves, saturation in light waves processing of a wider range of
● This phenomenon explains why diff instruments, despite frequencies
playing the same note, sound unique ○ Organ of Corti: Houses the hair cells which
The Pathway Inside the Ear: become displaced by vibrations in the basilar
The External/Outer Ear: Where our auditory system collects sound, membrane, causing them to convert the frequency
initial structure of the ear of the sound into an electrical signal
● The Pinna: The cone-shaped protuberances on the side of ■ Mechanical displacement of the hair
your head (what most people colloquially refer to as their cells allows positive ions from the
ear), acts like a satellite disk, directing sound waves into the extracellular fluid to enter the body of
ear canal the cell
● Ear Canal: Narrows as it moves towards the eardrum, ■ The loudness of the sound affects the
amplifies sound waves extent to which the hair cell bends + the
● Tympanic Membrane/ Eardrum: Thin membrane forming number of positive ions entering the cell
the back wall of the ear canal, separates outer and middle
