auditory and vestibular system

Question 1

what is the basic architecture of hair cells

Answer 1

-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

Question 2

function of the hair cell?

Answer 2

• 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

Question 3

the bundles are made of stereocilia - how are these stereocilia linked?

Answer 3

lateral-link connecters and tip-links

Question 4

what are lateral link connectors?

Answer 4

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

Question 5

what are tip links?

Answer 5

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

Question 6

what happens when the tip-links open?

Answer 6

• 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

Question 7

displacement of the cilia will cause?

Answer 7

depolarisation or hyperpolarisation

Question 8

what do fish and amphibians have?

Answer 8

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

Question 9

the inner ear is what up of what structures?

Answer 9

semi-circular ear canals and the cochlea

Question 10

the semicircular ear canals and the cochlea are part of which systems?

Answer 10

semi-circular ear canals - vestibular

cochlea - auditory

Question 11

another name for the vestibular and cochlear nerve?

Answer 11

• vestibulocochlear nerve

- 8th cranial nerve (comes form the auditor/vestibular system)

Question 12

what are the 2 types of motion?

Answer 12

linear and rotation

Question 13

what is linear motion?

Answer 13

• up and down
• left and right
• backwards and forwards

Question 14

what is rotation?

Answer 14

• roll, rotation around x axis, posterior
• pitch - rotation around y axis, anterior
• yaw - rotation around z axis, horizontal

Question 15

rotation causes what?

Answer 15

fluid movement in semi-circular ear canals

-hair cells at different entrances register different directions

Question 16

sensing rotation - mechanism

Answer 16

• 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

Question 17

there are also sensory receptors (hair cells) used to pick up linear motion - what are they called and how do they work?

Answer 17

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

Question 18

auditory system pathway

Answer 18

(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

Question 19

what is sound?

Answer 19

rapid variation in air pressure

Question 20

speed of sound, wavelength, frequency

Answer 20

wavelength = speed of sound/frequency

Question 21

what is normal air pressure?

Answer 21

100k pascals

Question 22

what is the pinna and its function?

Answer 22

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

Question 23

microtia - what is it, and different grades

Answer 23

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

Question 24

which microtia grade is the most common?

Answer 24

grade 3

Question 25

tympanic membrane

Answer 25

ear drum, vibrates in response to sound

Question 26

the point at which the tympanic membrane connects to the ossicles is called what?

Answer 26

the manubrium of malleus

Question 27

what are the ossicles and their role?

Answer 27

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

Question 28

what is glue ear?

Answer 28

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

Question 29

where does transduction happen?

Answer 29

inner ear

Question 30

what is in front of the oval window?

Answer 30

the stapes - stapes pushes on oval window, causing fluid compression

Question 31

cochlea and basilar membrane structure

Answer 31

stapes and oval window

scala vestibuli
scala media
scala tympani

round window

Question 32

where is the basilar membrane?

Answer 32

between the scala media and scala tympani

-critical to sound transduction

Question 33

what is the cochlea?

Answer 33

spiral fluid filled canal divided by a flexible membrane

Question 34

is the basilar membrane the same throughout its whole length?

Answer 34

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

Question 35

what is the organ of corti?

Answer 35

sits on top of the basilar membrane

-hair cells mounted on it (tectorial membrane is at the top of the hair cells)

Question 36

outer vs inner hair cells

Answer 36

outer acts as an amplifier, nothing else

inner do the hearing and transduction

Question 37

cochlear amplifier

Answer 37

• 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

Question 38

are quiet and loud sounds amplified?

Answer 38

quiet = yes
loud = no

Question 39

endolymph and amplification?

Answer 39

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