auditory and vestibular system Flashcards
what is the basic architecture of hair cells
-hair bundles are made of hairs/stereocilia and are filled with actin. They are stiff rods and rigid and sit on top of the hair cell
function of the hair cell?
- the hair cell converts stereocilia movement into neurotransmitter release - this is then converted into electrical activity
- hair cell synapses onto an auditory nerve fibre and projects the electrical activity to the brain
the bundles are made of stereocilia - how are these stereocilia linked?
lateral-link connecters and tip-links
what are lateral link connectors?
top connectors, shaft connecters and ankle links
-bundle the hairs together and make sure all the hairs move in the same direction at the same time
what are tip links?
found at the top of the cilia
- stereocilia bundle leans in a paticular direction, stretches the tip links
- the stereocilia is pulled and the top is disformed, allows +ve charge of ions into the stereocilia
- pushing the stereocilia in another direction will mean the ion channels are closed
what happens when the tip-links open?
- tip links stretched, ion channels open
- the fluid outside of the stereocilia known as endolymph is K+ rich
- potassium influx, cell depolarisation
- VGCC’s open, Ca2+ triggers neurotransmitter release at the synapse, moves to afferent neuron
- post-synaptic potential in nerve fibre triggers an AP
displacement of the cilia will cause?
depolarisation or hyperpolarisation
what do fish and amphibians have?
a lateral line system along the side of their body
- series of mechanoreceptors which detect and direction and velocity of water flow
- cupula encases the hair cell bundle, water will push against this cupula and act in the direction of the tallest stereocilia, opening up ion channels
the inner ear is what up of what structures?
semi-circular ear canals and the cochlea
the semicircular ear canals and the cochlea are part of which systems?
semi-circular ear canals - vestibular
cochlea - auditory
another name for the vestibular and cochlear nerve?
- vestibulocochlear nerve
- 8th cranial nerve (comes form the auditor/vestibular system)
what are the 2 types of motion?
linear and rotation
what is linear motion?
- up and down
- left and right
- backwards and forwards
what is rotation?
- roll, rotation around x axis, posterior
- pitch - rotation around y axis, anterior
- yaw - rotation around z axis, horizontal
rotation causes what?
fluid movement in semi-circular ear canals
-hair cells at different entrances register different directions
sensing rotation - mechanism
- at the entrance to canals there are ampulla which have sensory receptors (hair cells with cilia on top)
- cilia connected to gelatinous cupula
- fluid in canals lag due to inertia, cupula pulled in opposite direction to fluid rotation
- opens channels on air cells, afferent nerve fires
there are also sensory receptors (hair cells) used to pick up linear motion - what are they called and how do they work?
macula - utlricular and sacular
these hair cells are different because instead of detecting the motion of fluid, they detect the motion of crystals that sit on top of the extracellular matrix
- rigid layer of otoconia crystals
- when we move in a direction, this otolithic membrane also moves, stereocilia lean, ion channels open
auditory system pathway
(pneumonic) -outer ear, middle ear, inner ear come - cochlear nucleus on - olivary complex lectures - lateral meniscus in - inferior colliculus monkton - medial geniculate body ay - auditory cortex
what is sound?
rapid variation in air pressure
speed of sound, wavelength, frequency
wavelength = speed of sound/frequency
what is normal air pressure?
100k pascals
what is the pinna and its function?
size and shape varies from person to person
- gathers sound from the environment and funnels it to the eardrum - filters and influences the frequency response
- made entirely of cartilage, covered in skin
microtia - what is it, and different grades
developmental problems with the pinna
GRADE 1 - small developmental problems with the ear, small but present ear canal
GRADE 2 - closed ear canal causing hearing loss, partially developed ear (top part underdeveloped)
GRADE 3 - absence of ear canal, ear drum and external ear structures, peanut like structure
GRADE 4 - absence of entire ear
which microtia grade is the most common?
grade 3
tympanic membrane
ear drum, vibrates in response to sound
the point at which the tympanic membrane connects to the ossicles is called what?
the manubrium of malleus
what are the ossicles and their role?
the smallest bones in the human body
- in the middle ear
- connects the tympanic membrane to the oval window of the cochlea
- vibrational movement of the tympanic membrane transmitted through ossicles, amplified through incus and leads to pushing of the cochlea
what is glue ear?
chamber between ear drum and cochlea filled with air, but with glue ear its filled with a viscous/gluey fluid
-ear drum now pushes against fluid, losing amplification and the ability to hear
where does transduction happen?
inner ear
what is in front of the oval window?
the stapes - stapes pushes on oval window, causing fluid compression
cochlea and basilar membrane structure
stapes and oval window
scala vestibuli
scala media
scala tympani
round window
where is the basilar membrane?
between the scala media and scala tympani
-critical to sound transduction
what is the cochlea?
spiral fluid filled canal divided by a flexible membrane
is the basilar membrane the same throughout its whole length?
no, the end closest to the stapes/oval window is more rigid, will respond to higher frequencies
-the other end is floppier, bigger movements of membrane
what is the organ of corti?
sits on top of the basilar membrane
-hair cells mounted on it (tectorial membrane is at the top of the hair cells)
outer vs inner hair cells
outer acts as an amplifier, nothing else
inner do the hearing and transduction
cochlear amplifier
- basilar membrane moves up and down, pushing the hair cells towards the tectorial membrane - this then moves up and down, pushing the hair cells sideways. Opens up ion channels, +ve ion influx, afferent nerve fires.
- cell voltage increases, causing contraction, which pushes the basilar membrane up even further - now the inner hair cells touch the tectorial membrane, causes even great ion flux into the inner hair cells - huge amplification
are quiet and loud sounds amplified?
quiet = yes loud = no
endolymph and amplification?
K+ rich fluid, changes in voltage much more rapid than normal neurons
- if the scala media fluid wasn’t so K+ rich, amplification (inner hair cell output) would be reduced by half
- outer hair cells need to endolymph to make them as motile as they are
