Auditory and vestibular systems Flashcards
What are hair bundles made up of?
Made of actin(Stereocilia)
Where are hair bundles located?
They sit on top of the hair cells
What do hair cells synapse to?
Synapses on to the auditory nerve fibre and projects to the brain
What do hair cells over motion of and into what?
Convert motion of the stereocilia into release of neurotransmitter
What is the overlying cell matrix in auditory organs?
Tectorial membrane in auditory organs
What is the overlying cell matrix in the maculane?
Otoconial membrane in maculane
What is the overlying cell matrix in cristae?
Cupula in cristae
What can stereocilia be connected via within the bundle?
Within the bundle, stereocilia can be converted via a number of links:
- Lateral links
- Tip links
What are examples of lateral link connectors?
- Top connectors
- Shaft connectors
- Ankle links
What is the job of lateral link connectors?
Job is to hold bundles together and to move as a unit
Where are top links found?
Found at the top of the cilia
What does tension in the top link cause and allow?
Tension in the tip link distorts the tip of the stereocilia mechanically
-This allows channels to open and close with cilia movement. Current flows in proportionality
How do hair cells work?
- Tip links open ion-channels
- Endolymph is high in K+ and depolarises the cell
- VGCC open
- Ca2+ triggers neurotransmitter release at the synapse
- Post synaptic potential in nerve fibre triggers an action potential
What does displacement in cilia cause?
Causes a change in membrane potential
What system do most fish and amphibians have along both sides of their body?
Most fish and amphibians have a lateral line system along both sides of their body
What do mechanoreceptors provide?
Mechanoreceptors provide information about movement through water or the direction and velocity of water flow
What are mechanoreceptors also known as?
Also known as neuromasts
Where are superficial neuromasts located?
Superficial neuromast are on the surface of the fish
What encases the hair cell bundle and what does it move in response to?
A gelatinous cupula encases the hair cell bundle and moves in response to water motion
Where is the auditory system and vestibular system located?
Both located in the inner ear
What is the inner ear formed of?
The inner ear is formed of:
- Semicircular canals(Vestibular system)
- Cochlea(Auditory system)
What is the vestibular system responsible for?
Responsible for balance and motion in mammals
What are semicircular canals used to sense?
Semicircular canals are used to sense rotation
What does rotation do?
- Rotation causes fluid motion in semicircular canal
- Hair cells at different canals entrances register different directions
What is posterior semicircular canal responsible for?
Responsible for roll
What is anterior semicircular canal responsible for?
Responsible for pitch
What is Horizontal semicircular canal responsible for?
Responsible for Yaw
What are the steps involved in the sensation of rotation?
- Cilia are connected to the gelatinous cupula
- Under motion, fluid in the canals lags due to inertia, pulling the cupula in the opposite direction to the rotation of the head
- Cilia are displaced, depolarising haircells
How are the hair cells arranged in the utricular macula?
Hair cells are arranged in an arching manner
What does the utricular macula do as we move in a sideways direction?
As we move in a sideways direction, they pick up motion
How are the hair cells arranged in the saccular macula?
Hair cells arranged in up, down, forward and backward direction
What can saccular macula detect?
Can detect motion up and down as well as forward and backward
What are included in the otolith organs?
- Saccule macula
- Utricular macula
How do the otolith organs work?
The hair cells in the otolith organs are topped by a rigid layer of otoconia crystals
-Under acceleration the crystal layer is displaced, deflecting the cilia
What is the auditory system made up of?
Ear–>Cochlea–>Cochlear nucleus–>Olivary complex–>Lateral lemniscus–>Inferior colliculus–>Medial geniculate body–>Auditory cortex
What is sound?
Sound is rapid variation of air pressure
What is the wavelength?
Is the distance between 2 peaks in the wave
What is the wavelength determined by?
Determined by the rate at which the compression and rarefaction of a wave occur
Equation for wavelength
λ=c/f
c=speed of sound(344m/s)
f=frequency
What is the human hearing range in uPa?
2uPa-200000000uPa
What is the decible scale and what is its equation?
-Is a log of ratio relative to 2uPa
20log10(amplitude/20)
What does the pinna do?
Gathers sound from the environment and funnels it to the eardrum
What is the pinna made entirely out of?
Made entirely from cartilage and covered with skin
How does the pinna filter sound?
- Flange adds a high frequency amplification
- Meatus amplifies low frequencies
- Chonca amplifies high frequencies
What is microtia?
It is a developmental problem of the pinna
How is mictotia scaled?
Severity graded 1-4
What is the tympanic membrane also known as?
Also known as the eardrum
What does the tympanic membrane do?
Vibrates in response to sound
What is the ossicles?
Smallest bone in the human body
What are the ossicles made up of and what are they?
Made up of 3 bones:
- Malleus
- Incus
- Stapes
What do the ossicles do?
Connect the tympanic membrane to the oval window of the cochlea
What is glue ear?
Its where the middle ear fills with fluid which impedes motion of ossicles
What does glue ear do?
Reduces middle ear gain, raising hearing threshold
What are the 3 chambers to the cochlea?
- Scala vestibuli
- Scala media
- Scala tympani
What is the cochlea?
The cochlea is a fluid filled space canal divided by a flexible membrane
What does the basilar membrane do?
Basilar membrane filters sound according to frequency
Where does the organ of corti sit?
Sits on top of the basilar membrane within the scala media
What is mounted on the organ of corti?
Inner and outer hair cells are mounted on it
What does motion of the organ of corti on the membrane cause
Motion of the organ of corti on the basilar membrane causes displacement of sterocilia
What do inner hair cells do?
Inner hair cells do transduction
What do outer hair cells do?
Outer hair cells are there to act as an amplifier
What does an influx of positive ions do to outer hair cells?
Influx of positive ions makes the outer hair cells contract
What happens to outer hair cells when ion channels are closed?
When ion channels are closed, prestin has a long conformation and the cell expands
What happens to outer hair cells when ion channels are opened?
When ion channels are open, prestin has a short conformation and the cell contracts
How does the cochlear amplifier work?
-As the basilar membrane moves upwards, it pushes against the tectorial membrane making the hair cells lean
-This allows an influx of positive ions in the outer hair cell
-An increase in voltage results in:
-Prestin in short conformation state
-Outer hair cell contracts
-This pulls the basilar membrane towards the tectorial
membrane
What does the endolymph create?
The high K+ concentration of the endolymph of the scala media creates a 2x amplification
What would happen if the endolymph were not K+ rich?
If the endolymph were not K+ rich, then inner hair cell output would be halved making sound quieter
