Week 2 Flashcards
basilar membrane
25-35mm
tonotopic
3 types of cochlear fluid in the organ of corti (location and voltage)
1) endolymph (scala media; +80mv; high concentration of /k+)
2) perilymph (vestibuli and tympani; 0mv charge)
3) cordalymph (fills area around inner and outer hair cells; 0mv; completely separated from endolymph)
tectorial membrane vibration in comparison to basilar membrane
vertical vibration with a characteristic frequency 1/2 octave below the basilar membrane
vibration of the reticular lamina (compared to BM)
*vibrates 6x faster than the basilar membrane near characteristic frequency
outer hair cells basics
3 rows (but not always neatly organized so 3-5)
- a/b 12,000
- cylinder shape with a charge of -70mv
- base to apex= 10-90 micro m
- have stereocilia that are embedded in the tectorial membrane which causes sheering
what do tip links and side links control?
mechano-electrical channels
*they are on the stereocilia of the OHCs and keep them together and allow them to open and close the METs (open and close the door)
what does MET stand for?
mechano-electrical channels
why does the cytoplasmic membrane of the OHCs have a very large mechanical stillness and why are they so rigid?
they are supposed to contract and elongate as part of their function and this allows them to do such without bending or breaking
*each OHC has a small cytoskeleton near the top to allow it to contract and elongate
Deiters’ cells
the phalangeal process forms the reticular lamina and the deiters’ cells form a cup holder or the OHC to allow it to “dance”
space of Nuel
full of chordalymph and is around the cells
Inner Hair cells basic facts and numbers
1 row
- 4000 total
- stereocilia is not embedded in tectorial stripe which runs along the bottom of the tectorial membrane where IHCs are
- flask shape with charge of -40 to -45mv
- **not as negative as OHCs because we just need them to fire while OHCs need to do more than just fire
the auditory nerve numbers of fibers
32000-37000
afferent fibers of the auditory nerve
come from hair cells and travel up to brain
- 90-95% of nerve fibers
- type 1 is more myelinated which helps transmit impulse better, innervates IHCs
- type 2 innervates OHCs
- –lots of fibers per IHC, each type 2 fiber goes to many OHCs
efferent fibers of the auditory nerve
(1700-1800) 5-10% of nerve fibers
*they go from the brain to the ear
neurotransmitter in the auditory system released from hair cells to nerve fibers
glutamate
tonotopic organization of the auditory nerve
carries the tonotopic organization of the cochlea, low in the core and high in the periphery
excitation of hair cells
when the stereocilia go to stria vascularis, channels open and allow potassium in
*depolarization
inhibition of hair cells
when stereocilia go away from stria vascularis and towards the modiolus, they close the channels (hyperpolarization/repolarization)
k+ role hair cells
goes into hair cell during depolarization and is not allowed in during hyperpolarization
*goes in casually during cell rest
Ca +2 role in hair cells
with depolarization of the cell, the gates on the sides of the hair cell open and allow calcium in calcium takes the glutamate vessicles and drives them to the bottom of the cell were they are released
*when calcium goes in, i moves K+ out to help with hyperpolarizations
K+ cycling back to endolymph
- Deiters’ cells take the K+ from the hair cells which pass it through gap junctions to the scala media again
- –this process is affected by the most common type of non-syndromic HL which is Cx26 which affects the gap junctions (which means k+ has no way back to endolymph so loss of voltage so no cell functioning
what are the two functions of OHCs obtained through electromotility
- frequency selectivity
* amplification of soft signals (by 40-60dB)
Inner hair cell function
transduction of signal to brain
*hensen’s stripe of stereocilia helps to open channels and depolarize cell by coming down and helping to sheer stereocilia
electromotility of OHCs
part of what we are measuring in OAEs
- hair cells shrink with depolarization and grows longest with condensation (hyperpolarization)
- this process is driven by prestin which uses the intracellular anion chloride (Cl-) as a voltage sensor
- –chloride is in the cell and is part of what makes the cell negative
olivocochlear bundle (OCB)
- 1400 neurons is cats, 1700-1800 in monkeys
- originates in the superior olivary complex and extends to the cochlea
- greater number of fibers at the middle and basal turns (of the cochlea?)
pathways of the OCB (2)
- crossed (bi-crossed) is ipsilateral
- uncrossed is contralateral
- some g through the cochlear nucleus and the rest go through he vestibular branch
lateral olivocochlear fibers (LOC)
- about 900 neurons
- –smaller cell bodies and unmyelinated axons
- 15% are crossed and 48% are uncrossed
- they form axodendrite synapses which means they innervate the IHCs and synapse on the type I afferent fibers synapsing on the IHCs
- hypothesis is they control the firing rate of those neurons they synapse to
medial olivocochlear fibers (MOC)
- about 500 neurons
- –larger cell bodies and large myelinated axons
- 26% crossed and 11% uncrossed
- they form axosomatic synapses which means they synapse directly to the OHCs
- there are more neurons for the 1st row (each neuron innervated many cells
two neurotransmitters of the OCB
- released by efferent fibers
- –ACh=acetocholyne
- –GABA= seen towards the apical cochlea OHCs
two modes of activating the efferent system
- electrical= sticking an electrode into those fibers which is usually done at the 4th ventrical level which stimulated crossed fibers
- acoustical= stimulated by noise (broadband generally) with a latency of 40msec which is similar to that of reflexes
how the MOCs work
release of acetyocholine activated calcium channels of hair cell membrane allowing calcium to enter the cell
- the more calcium channels open the faster the release of K+ making the cell more negative and suppressing electromotility
- –fast effect=w/in 100msec and is axial stiffness reduction which reduced electromotiity
- –slow effect= with 100 sec which increasing the resting potential, changing the operating point (shift)
importance of the MOC (3)
- protection from loud noises
- understanding speech in noise (MOC fibers try and suppress background noise)
- attention
