Auditory & Vestibular Systems Flashcards
What are hair bundles filled with?
→ actin and are stiff rods
What do hair cells synapse onto?
→ Auditory nerve fibre that projects to the brain
What do hair cells convert?
→ Motion of stereocilia into release of neurotransmitter
→ NT is converted into electrical activity
What is the extracellular matrix of the hair cells called?
→tectorial membrane
Where is the otoconial membrane?
→ In the macula of the vestibular system
Where is the cupula?
→ Cristae of vestibular system
How are stereocilia arranged?
→ In bundles
What are stereocilia connected by?
→ connectors
What are the 3 types of connectors?
→ Top connector
→ Shaft connector
→ Ankle links
What connectors are important to transduction?
→ tip links
What is the function of lateral link connectors?
→ they hold the bundle of stereocilia together to allow it to move as a unit
What is the function of tip links?
→ Tension in the tip links distorts the tip of the stereocilia mechanically
→ distortion allows channels to open and close with cilia movement
→ current flows proportionately
Describe how hair cells work
→ Tip links open ion channels
→ outside the stereocilia is a fluid called endolymph
→ when tip links deform and pull on the top of the stereocilia they allow in a lot of K+
→ endolymph is high in K+
→ K+ influx depolarises the cell
→ VGCC opens
→ Ca2+ triggers neurotransmitter release at the synapse
→ postsynaptic potential in nerve fibre triggers an action potential
When does depolarisation occur?
→ When the hair bundle is pushed towards the tallest stereocilia
When does hyperpolarisation occur?
→ When the hair bundle is pushed away from the tallest cilia
What system do fish and amphibians have?
→ Lateral line system
What is the function of mechanoreceptors on fish?
→ Provides information about movement through water or the direction and velocity of water flow
How do neuromasts function?
→ Gelatinous cupula encases the hair bundle and moves in response to water motion
What is the inner ear formed from?
→ Semicircular canals from the vestibular system
→ Cochlea
Where do the afferent nerves come from?
→ Vestibulocochlear nerve CN VIII
What is linear motion?
→ Up, down
→ left and right
→ back and forwards
What is rotation?
→ Rolling - shoulder to shoulder
→ pitch - forwards and backwards
→ yaw - side to side
What senses rotation?
→ Semicircular canals
What is responsible for sensing roll?
→ Posterior semicircular canal
What is responsible for sensing pitch (y-axis)?
→ Anterior semicircular canal
What is responsible for sensing yaw?
→ Horizontal semicircular canal
Where does the endolymph move?
→ In the opposite direction to your head
What does rotation cause in the semicircular canals?
→ Fluid motion
What are cilia connected to?
→ Gelatinous cupula
Describe what happens in the cupula when motion occurs
→ Fluid in the canals lags due to inertia pulling the cupula in the opposite direction to the rotation of the head
→ cilia are displaced and depolarise hair cells
What is the ampulla?
→ AN opening with receptors
What does the cupula detect?
→ Flow of fluid through the semicircular canal
What are the otolith organs sensitive to?
→ Linear acceleration
How are the hair cells arranged in the utricular macula?
→ in a curving way
What motion can the saccular macula detect and why?
→ up and down motion
→ hair cells are arranged in that way
What is on top of the hair cells? (vestibular)
→ Rigid otoconia crystals
What happens to the crystals when motion occurs?
→ Under acceleration the crystal layer is displaced which deflects the cilia
Describe the auditory pathway
→ Cochlear nucleus
→ Olivary complex
→ Lateral lemniscus
→ Inferior Colliculus
→ Medial geniculate body
→ Auditory cortex
What type of pressure waves are in the atmosphere?
→ Longitudinal
What determines wavelength?
→ Rate at which compression and rarefaction occur
What determines frequency?
→ Rate at which pressure cycles between compression and rarefaction
What is normal air pressure?
→ 100kpa
What is the decibel scale?
→ Log of ratio relative to 20 micropascals
What is the pinna?
→ Visible ear
What is the function of the pinna?
→ Gathers sound from environment and funnels it to the eardrum
What is the pinna made from?
→ Cartilage and is covered with skin
What is the function of the meatus and the concha?
→ meatus amplifies low frequency
→ concha amplifies high frequency
What is grade I microtia?
→ Less than complete development of external ear
→ identifiable structures and a small but present ear canal
What is grade II microtia?
→ Partially developed ear
→ closed stenotic external ear canal producing conductive hearing loss
What is grade III microtia?
→ Absence of the external ear
→ small peanut like vestige structure
→ absence of external ear canal and drum
What is grade VI microtia?
→ Absence of the total ear
What does the eardrum vibrate in response to?
→ Sound
What do the ossicles connect?
→ Tympanic membrane to oval window of cochlea
What does the malleus connect to?
→ Eardrum
What does the incus act as?
→ A lever
→ malleus pushes it at the top which gives it amplification
What does the incus connect to?
→ Stapes
How does the motion of the eardrum turn into motion of fluid in the cochlea?
→ Vibrational movement in the ear drum is transmitted through ossicles and amplified at the incus
→ leads to motion pushing on the oval window of the cochlea
What is glue ear?
→ Middle ear fills with fluid which impedes motion of the ossicles
Why do you lose amplification with glue ear?
→ Eardrum is pushing against fluid
What are the three chambers in the cochlea?
→ Scala vestibuli
→ Scala media
→ Scala tympani
What is the basilar membrane?
→ between the scala tympanis and the scala media
What does the stapes cause?
→ Compression of fluid within cochlea
What is the cochlea?
→ Fluid filled spiral canal divided by a flexible membrane
What is the function of the basilar membrane?
→ It filters sound according to frequency
What is the basilar membrane like at the apex and at the end?
→ more rigid at the end closest to oval membrane
→ at the apex it is wide and compliant
How does the basilar membrane resonate at the apex and at the end?
→ Close to the oval window the basilar membrane resonates at higher frequencies
→ at the other end it resonates at lower frequencies
→Wave rises gradually, peaks, then decays rapidly.
→Peak location depends on stimulus frequency.
Where is the organ of corti?
→ On top of the basilar membrane within the scala media
What is the extracellular matrix of the organ of corti?
→ Tectorial membrane
What does motion of the organ of corti cause?
→displacement of stereocilia
What hair cells are in contact with the tectorial membrane?
→ outer hair cells
What does the basilar membrane do to the hair cells?
→ Moves up and down and pushes the hair cells towards the tectorial membrane
Describe how the cells contract
→ Influx of +ve ions makes the outer hair cells contract
→ when there are increases in voltage the prestin contracts
→ it is on the cell membrane so it causes the entire cell to contract
What is prestin?
→ A substance that allows the hair cell to be motile
Describe the cochlear amplifier
→ basilar membrane moves upwards
→ it pushes against the tectorial membrane which makes the hair cell bundle lean
→ as it leans it opens up the channels on the hair cell
→ this allows an influx of +ve ions
→ the voltage inside the cell increases
→ the cell contracts
→ prestin will be in a short confirmation state
→ basilar membrane is pulled towards the tectorial membrane
→ inner hair cell leans in further which causes the influx of more +ve ions
How much does the cochlea amplify by?
→ 50 dB
What is the intracellular voltage of the hairs?
→ negative
What is the difference like between intra and extra cellular voltage and why?
→ Much larger than other neurons
→ changes in the voltage of haircells are much more rapid
What ion is in high concentration in the scala media?
→ K+
What is a difference between inner and outer hair cells?
Inner hair cells have afferent synapse to the brain
→arranged in rows
Outer hair cells have efferent synapse
→arranged in lined arches
Summarise the 3 ways sound amplified in the year
→outer cells structure
→ossicles via levering
→battery- difference in potential difference between endolymph and actual hair cells.
