Auditory system chapter 13
Sound is the movement of air particles and has wave-like The two compartments of the cochlea contain fluid with different
properties. Sound waves consist of amplitude, which is the concentrations. The Scala media contains endolymph that has high
volume, and frequency, which is the pitch of the sound. Sound K+ and low Na+ concentrations, which drives K+ into the cell. Scala
waves are composed of phases, multiple phases after another are tympani contains perilymph that has high Na+ and low K+
called a waveform. concentrations.
Endolymp has a potential of +80 mV and the perilymph (hair cells)
Frequency and amplitude have a potential of -45 mV. The organ of Corti, where the hair
1) quiet and low pitch cells are located, therefore has a potential difference of 125 mV,
2) Loud and low pitch which means that there is a high driving force of K+ into the hair
3) Quiet and high pitch cells. Though, the hair cells have a high concentration of K+, which
4) Loud and high pitch means that the K+ can both hyperpolarise and depolarise the hair
cell very fast.
The ear
The external part of the ear collects sounds and boosts
frequencies around 3 kHz, human speech is around 2-5 kHz.
The middle ear is filled with fluid and can amplify the sound
energy to 200-fold, due to pressure focus from the large
tympanic membrane to the small oval window. The tympanic
membrane consists of ossicles that connect the membrane to the
inner ear. The inner ear consists of the cochlea that transduces Stereocilia
sounds to neural signals, all the neuronal cells that process sound Stereocilia are linked to the tectorial membrane, so when the
is also filled with fluid. membrane moves, the hair cells will also move and
mechanoelectrical transduction takes place due to the opening of
the ion channels during the movement.
Mechanoelectrical transduction
1) Stereocilial K+ channels open and K+ enters the cell
2) The cell depolarises and this opens calcium channels (lower side)
The cochlea 3) Calcium flows into the cell, which releases neurotransmitters
The cochlea is the place where sound is detected by the hair that open somatic K+ channels and calcium-dependent K+ channels
cells that are located in the organ of the Corti. The hair cells are 4) K+ channels are open at the base of the cells, so the movement
located in rows, the first row contains the inner hair cells that in the opposite direction results in hyperpolarisation
are important for sound transduction. 5) The hair cells exploit their different milieus to provide extremely
fast and energy-efficient repolarisation
When the sound moves from the scala vestibule to the scala
tympani, the tectorial membrane starts moving so that the
stereocilia of the hair cells, which lay just underneath the
tectorial membrane, can move along with it. This movement is
crucial for the opening of calcium channels within the hair cell to Ribbon synapses
conduct neuronal signals. Ribbon synapses are sites of contact between neurons that are
specialised for the rapid transmission of signals by calcium-
triggered secretion of neurotransmitters. This enables neurons to
transmit signals over a dynamic range of several orders of
magnitude and intensity.
Sound is the movement of air particles and has wave-like The two compartments of the cochlea contain fluid with different
properties. Sound waves consist of amplitude, which is the concentrations. The Scala media contains endolymph that has high
volume, and frequency, which is the pitch of the sound. Sound K+ and low Na+ concentrations, which drives K+ into the cell. Scala
waves are composed of phases, multiple phases after another are tympani contains perilymph that has high Na+ and low K+
called a waveform. concentrations.
Endolymp has a potential of +80 mV and the perilymph (hair cells)
Frequency and amplitude have a potential of -45 mV. The organ of Corti, where the hair
1) quiet and low pitch cells are located, therefore has a potential difference of 125 mV,
2) Loud and low pitch which means that there is a high driving force of K+ into the hair
3) Quiet and high pitch cells. Though, the hair cells have a high concentration of K+, which
4) Loud and high pitch means that the K+ can both hyperpolarise and depolarise the hair
cell very fast.
The ear
The external part of the ear collects sounds and boosts
frequencies around 3 kHz, human speech is around 2-5 kHz.
The middle ear is filled with fluid and can amplify the sound
energy to 200-fold, due to pressure focus from the large
tympanic membrane to the small oval window. The tympanic
membrane consists of ossicles that connect the membrane to the
inner ear. The inner ear consists of the cochlea that transduces Stereocilia
sounds to neural signals, all the neuronal cells that process sound Stereocilia are linked to the tectorial membrane, so when the
is also filled with fluid. membrane moves, the hair cells will also move and
mechanoelectrical transduction takes place due to the opening of
the ion channels during the movement.
Mechanoelectrical transduction
1) Stereocilial K+ channels open and K+ enters the cell
2) The cell depolarises and this opens calcium channels (lower side)
The cochlea 3) Calcium flows into the cell, which releases neurotransmitters
The cochlea is the place where sound is detected by the hair that open somatic K+ channels and calcium-dependent K+ channels
cells that are located in the organ of the Corti. The hair cells are 4) K+ channels are open at the base of the cells, so the movement
located in rows, the first row contains the inner hair cells that in the opposite direction results in hyperpolarisation
are important for sound transduction. 5) The hair cells exploit their different milieus to provide extremely
fast and energy-efficient repolarisation
When the sound moves from the scala vestibule to the scala
tympani, the tectorial membrane starts moving so that the
stereocilia of the hair cells, which lay just underneath the
tectorial membrane, can move along with it. This movement is
crucial for the opening of calcium channels within the hair cell to Ribbon synapses
conduct neuronal signals. Ribbon synapses are sites of contact between neurons that are
specialised for the rapid transmission of signals by calcium-
triggered secretion of neurotransmitters. This enables neurons to
transmit signals over a dynamic range of several orders of
magnitude and intensity.
