Sound Conduction and Transduction Flashcards
What % of UK population suffer from hearing loss
10%
Main causes of hearing loss? (5)
Loud sounds Genetics Infections such meningitis Drugs used for severe heart infections and chemo Ageing
Hearing range of humans in Hz?
20Hz to 20kHz
1 Hertz = 1 X per second
Cycle
The ear can detect movements as small as …
a fraction of a nanometer, size of water molecule
We Watt range can we hear
1x10-12 to 1W
Outline sound detection:
Sound penetrates ear and causes tympanic membrane to vibrate
The vibration is transmitted to the cochlear which has hair cells along its length. when the hair cell deflects due to vibration we detect sound.
How many ossicles in an ear
3
Role of the ossicle?
To facilitate transmission of tympanic membrane vibration to the cochlear
What must the ossicle do to be able to carry out its role well
Match the impedance of the tympanic membrane and so reduce the loss in energy as the vibration goes from the air to the cochlea
The impedance measures ….
reluctance of a system in receiving energy from a source.
reluctance of a system in receiving energy from a source is called …
Impedance
resonant frequency is the …
The frequency at which the impedance of the system is minimal
The frequency at which the impedance of the system is minimal is called
resonant frequency
What controls the tension of the tympanic membrane (muscle and what the muscle controls)
Malleus and Incus position can be adjusted by the tensor tympanic muscle and stapedius muscles to control the tension of the tympanic membrane.
What muscles control tension of the tympanic membrane
Tympanic muscle and stapedius muscle
What is conductive hearing loss
when the ear is not capable of transmitting the vibration of sound waves onto the cochlea
What can cause conductive hearing loss in children
fluid accumulation in the middle ear is a common
cause of conductive hearing loss (cold)
What can cause conductive hearing loss in adults (3)
• Barotrauma is a temporary form of conductive hearing loss
An abnormal growth of bone (otosclerosis) can obstruct the ear
canal.
A perforated tympanic membrane is a form of conductive hearing
loss.
What is in the organ of Corti (4)
Basilar and tectorial membranes, the hair cells and and supporting cells
How does sound vibration cause movement in the Organ of Corti
The motion of the stapes generates a difference in pressure between the two liquid-filled chambers of the cochlea which in turns causes the vibration of the basilar membrane
On top of the basilar membrane are hair cells which on top of that has the tectorial membrane. the relative movement of the tectorial and basilar membrane due to the difference in pressures of the two chambers of the ear bends the air bundles adjacent to the hair cell which allows detection of sound
The basilar membrane is an X structure that vibrates at different Y in response to different frequencies
elastic
positions along its length
How does the impedance of the basilar membrane vary along its length, and what does this do to the local resonant frequency
Start is narrow and tough end is broad and floppy
this means the resonant frequency is different along its length
What are the microvilli of hair cells known as
Stereocilium
What is a hair cell characterised by
Bundles of 3 rows of stereo cilia
What is mechanotransduction of hair cells
The bending of stereocilia towards the tallest stereocilium (we can use a glass probe) changes the internal voltage of the cell, ultimately producing an electric signal that travels towards the brain. This is called Mechano-transduction (MT
Stereocilia are connected by XXXXX
filamentous linkages called tip links.
What ion is needed for stereo cilia to transmit noise
Ca
How does bending of stereo cilia produce an electrical current
Bending stretches the tip links connecting stereo cilia which in turn results in the opening of ion channels and a current generation and action potentials etc etc
Explain why the bending of stereo cilia producing an electrical current is not a passive process but an active one. What does the active work?
If we measure the stiffness of the tip links, before it pull the channels open tension increases, and after the channel opens the tension SHOULD decrease (think pulling door with a spring) however the tip link tension becomes negative, suggesting it actively does some work.
This is caused by the basilar membrane
Why is the active process of sound conduction in the hair cells necessary in sound conduction
A large portion of energy generated by sound is lost in the viscous damping effects of the cochlear liquids
4 aspects of the active process of hair cells in sound conduction?
Amplification
Frequency tuning
Compressive nonlinearity
Spontaneous otoacoustic emission
Explain amplification aspect of the active process of hair cells in sound conduction?
Basilar membrane amplifies the relevant frequency of the stimulus
Explain the frequency tuning aspect of the active process of hair cells in sound conduction?
If you increase the amplitude of your stimulus, the basilar membrane will concentrate the sound at a particular frequency
Explain the Compressive nonlinearity aspect of the active process of hair cells in sound conduction?
The hair cells basilar membrane amplifies low intensity sounds a lot more than high intensity sounds
Explain Spontaneous otoacoustic emission aspect of the active process of hair cells in sound conduction?
if the active process is working well in a basilar membrane, a healthy human ear emit one or more pure tones when in a quiet environment
2 types of hair cells? which is more common
Inner and outer
outer is more common
Difference in 2 types of hair cells structure?
Outer hair cells have a V/U shaped bundles
Inner have a linear shaped hair bundle
Where do most afferent projections of sound originate from
Inner hair cells
Where do most efferent projections from the brain project to
Outer hair cells
What is the role of outer hair cells?
help in Frequency selectivity and sensitivity enhancing
What happens in electro mobility and what rate does it happen at
heir cell body shortens and elongates when their internal voltage is changed. This is called electromobility and can happen at a rate of 80 kHz
due to the reorientation of the protein prestin.
Hair cells (mostly IHCs) form synapses with sensory neurons in the XX
cochlear ganglion (spiral ganglion).
What is different about ganglion cells regarding their detection of frequencies
Each ganglion cell responds best to stimulations at a particular frequency.
Where does tonotopic mapping begin
In the cochlear ganglion
In the spiral/cochlear ganglion, Neurotransmitters are X at rest, but the rate changes in response to Y
(as a result of MT ion channel gating)
continuously released
a change of the presynaptic voltage
What is tonotopic mapping
spatial arrangement of where sounds of different frequency are processed in the brain
How do we encode middle and high frequency sounds considering the frequency is too high for a neuron to repeatedly fire and encode
We have multiple fibres which are phase locked that give a collective response at a frequency that single nerve fibres couldn’t manage individually
sensorineural hearing loss is when the problem is in the …
sensory apparatus of the Inner ear or
in the vestibulocochlear nerve (retrocochlear hearing loss)
the most widespread type of hearing loss is …
sensorineural hearing loss
Causes of sensorineural hearing loss? (6)
Loud noises, headphones at high volume can cause temporary
or permanent hearing loss (Club: ~100 dB, Rock concert:
~120 dB)
• Ménière’s disease: excess of fluid in the cochlea
• Many genetics mutations affect the Organ of Corti
• Aminoglycoside antibiotics are toxic for hair cells
• Congenital diseases (rubella, toxoplasmosis)
• Ageing (presbycusis).
Hearing loss is primarily due to …
the loss of hair cells
How do cochlear implants work
bypass the dead cells and stimulate the nerve fibres directly: detect sounds, break them down into their constituent
frequencies and send the signal directly to the auditory nerve via antennas
Path from Sound to the right auditory cortex? (8)
Sound Cochlea Auditory nerve fibre Ipsilateral cochlear nucleus Superior olivary nucleus Inferior colliculus Medial geniculate nucleus Right auditory cortex
What is the tonotopic arrangement of neurons in the cochlear nucleus
(low frequencies
ventrally, high frequencies dorsally).
What nucleus is responsible for locating the direction of high frequency sounds
dorsal cochlear nucleus
What are spectral cues.
The ears detect and affect differently sounds coming from different directions due to their asymmetrical shape of the ear and the fact that high frequency sounds are wavelengths of the size of our head/ear/shoudlers
What is the dorsal cochlear nucleus responsible for
locating the direction of high frequency sounds in the vertical plane
what neurons are present in the cochlear nucleus (2)
T-STELLATE CELLS
BUSHY CELLS
Which nucleus identifies direction of sounds in the vertical plane
dorsal cochlear nucleus
Which nucleus identifies direction of sounds in the horizontal plane
Superior olivary complex
Superior olivary complex does what
compares the bilateral activity of the cochlear nuclei
MEDIAL SUPERIOR OLIVE does what
the interaural time difference is computed: sounds are first
detected at the nearest ear before they reach the other one.
What cells are important in the medial superior olive
Bushy cells
LATERAL SUPERIOR OLIVE does what
The LSO detects differences in intensity between the two ears (if a sound originates in the left it will be perceived louder in the left ear).
A map of
interaural delay can be formed due to XX(birds).
DELAY LINES
What happens at the INFERIOR COLLICULUS (2)
Here responses from different frequencies merge. In the IC all ascending
pathways converge and collateral sounds (e.g. talking bouncing off a wall) is filtered out
What are the three parts of the inferior colliculus
entral nucleus, dorsal cortex and
external cortex
Which part of the inferior colliculus is tonotopically arranged
central nucleus
What is the precedence effect
Collateral sounds (e.g. talking bouncing off a wall) are filtered out
What happens at the superior COLLICULUS (2)
Here auditory and visual maps merge.
The auditory map here created is fundamental for reflexes in orienting
the head and eyes to acoustic stimuli.
The primary auditory cortex A1 is located in the ….
superior bank of the
temporal lobe
Mapping of the auditory cortex?
Tonotopic
What else is mapped in the auditory cortex apart from tone?
Loudness, rate, frequency modulation
at what point in the auditory pathway is the earliest point tonotopic mapping starts
basilar membrane
