Inner Ear Review 3 Flashcards
What is the partition consisted of?
BM, tectorial membrane, organ of corti
Tonotopic arrangement
Different regions of the basilar membrane vibrate at different sinusoidal frequencies due to variations in thickness and width along the length of the membrane
he place of basilar membrane motion is thought to be directly related to perceived
pitch
Process of the hair cells transmitting NT to the cochlear nerve
- Tectorial membrane moves and stimulates the stereocilia
- Links on the stereocilia open to allow potassium to flow into the cell (depolarizes)
- Calcium flows into the cell through ion channels
- Triggers glutamate+ to go to the synaptic cleft
Process of the refractory period after a hair cell fires
- Potassium is reabsorbed into the cortilymph
- Stria vascularis takes up potassium again to recycle it into the endolymph
If the fluid moves the hair cells from tall to short, this will:
Inhibit the influx of potassium (hyperpolarize)
What factors help us sensory code sounds?
intensity frequency pitch
Why do we need the hair cells to “sharpen” the incoming signals?
to differentiat between pitches/frequencies (aka active mechanism)
Absolute refractory period
time during which another action potential is impossible; limits maximal firing rate
relative refractory period
the period of time following an action potential, when it is possible, but difficult, for the neuron to fire a second action potential, due to the fact that the membrane is further from threshold potential (hyperpolarized)
4 characteristics of an action potential
- Self propogating
- Forward transmission
- Unidirectional
- No degradation over time
the place of the basilar membrane motion is related to ____
frequency and pitch
the BM is ____ and ____ at the base
narrow and stiff (high frequencies)
the BM is ____ and ____ at the apex
wide and floppy (low frequencies)
what type of frequencies are more suceptible to damage?
high frequencies (at the base, get all input all the time)
primary function of inner hair cells
send information about sound to the brain
axosomatic
nerves that connect an axon to a soma
shape of outer hair cells
test tube shaped, don’t have a bulge
shape of inner hair cells
flask shaped, have a bulge in the middle
what are the main afferents?
IHC
What are the main efferents?
OHCs
What is the kinocilium?
guiding body for the hair cell stereocilia to align during embryologic development
What happens to kinocilium after birth?
becomes rudimentary
stereocilia are arranged by what factor
height
stereocilia connect to each other through
tips and side links
What is one major difference in OHC?
lined with prestin (matrix like format and form of muscle tissue for movement)
how many OHC do humans have?
12,000
How many IHC do we have (in total)?
4,000
Are frequency ranges among different species the same?
no, vary due to the size of hearing systems
most common type of cochlear damage
OHC damage
what type of loss is associated with OHC damage
sensory HL, 40 dB loss, mild to moderately severe
if both IHC and OHC are gone, what degree of hearing loss will we have?
severe to profound
most common neurotransmitter in ear
glutamate
What kind of sound stimuli do the OHC amplify?
low (0-40dB)
What is our auditory accessory structure?
tectorial membrane
Is the receptor potential directly transmitting information to the receptor neuron?
No, it doesn’t directly transmit information… goes through the synaptic cleft
What excites the neuron
neurotransmitter
If fluid moves the hair cells from short to tall, this will:
Excite the system, cause an influx of potassium (depolarize)
What do we know about the action potentials of a hair cell at rest?
there are still firings happening
What physical property of sound determines the displacement of the basilar membrane?
frequency
How is neural firing different than cochlear nerve firing?
Sodium influx in brain instead of potassium firing in cochlea, potassium outflux in brain
3 factors that influence encoding
intensity
frequency
firing code
three factors when encoding intensity
rate
how many
fibers
2 factors when encoding frequency
tonotopic organization
phase locking
4 factors related to the firing pattern codes of OHC
Onset
duration
offset
envelope
what makes a tuning curve “sharp” ?
amplification of the OHC (active mechanic amplifiers)
if we have damage to the OHC, what will we see on a tuning curve?
“broad” tuning, not sharp
what do our efferent fibers do for the inner ear system?
modulate / modify the OHC activity
in what ways do the efferent fibers modulate the OHC activity?
- reduce masking
- selective attention
- protect from intense sound
- balance input from both ears
how do OHC improve our sensitivity?
they make response thresholds lower (compress them –> nonlinear system)
what are the cochlear receptors
IHC
what do the IHC do?
generate receptor potentials (afferent)
what crosses the synaptic cleft to stimulate CN 8 nerve fibers?
neurotransmitter (most common in aud system is glutamate+)
at what point is an action potential generated?
when there is sufficient neurotransmitter
how is neural firing different than cochlear firing?
NaK pump instead of just K (potassium)
what concept explains why low frequencies can mask high frequencies but not vice versa?
upward spread of masking
can a 200 Hz tone maska 1,000 Hz tone?
yes, upward spread of masking
what do we know about the lowest point of the graph while looking at a tuning curve?
it is the characteristic frequenchy
what is a PSTH
post-stimulus time histogram
how do we graph a post-stimulus time histogram?
number of firing neurons on the y axis and time on x axis in milsec
what does a “primary” or “primary-like” PSTH look like?
rest - peak - rest (initial spike and nothing else)
describe a “pauser” response (PSTH)
spike – pause – buildup (primary with a pause)
describe an “onset-chopper” response (PSTH)
spike – rest – spike – rest – spike – rest (increasing rest thresholds)
is there only one type of cell in the cochlear nuclei?
no, there are pyramidal, octopus, stellate, spherical, and globular
what are 2 excitatory neurotransmitters in the AVS
glutamate and aspartate (amino acids)
what are 2 inhibitory neurotransmitters in the AVS
GABA and glycine
what are 2 neurotransmitters in the “efferent” AVS pathway
acetylcholine and noradrenaline
8CSlima
- 8th nerve
- cochlear nucleus
- superior olivary complex
- lateral lemniscus
- inferior colliculus
- medial geniculate body
- auditory cortex (A1)
What are the two largest categories of ototoxic drugs?
aminoglycocide and some members of the platinum chemotherapy drug family (carboplaton)
Best describe the sodium-potassium pump
The main function of the pump is to maintain the resting potential by actively moving sodium out of the cell and potassium back in to restore the proper balance.
Based on the 5 important functions of cell membrane proteins, clearly describe 3 of the important functions of such proteins that are on or in the cell membranes?
One important function of cell membrane proteins is that they have transmembrane ion channels that determine the electrical activity of the cell.
Another important function of cell membrane proteins is that they act as enzymes to catalyze biochemical reactions.
Cell membrane proteins also act as carrier proteins to help things cross the cell membrane. These carrier proteins can either be passive or active transport. When a carrier protein is an active transporter, it requires ATP.
Briefly state two ways in which auditory nerve fibers are able to encode the frequency of an auditory stimulus.
Auditory nerve fibers encode frequency of auditory stimulus by the tonotopic arrangement of the cochlea. Different regions of the basilar membrane vibrate at different sinusoidal frequencies based on the thickness and width along it. The basilar membrane is designed so that it has a best region to vibrate for every frequency. For example, how high frequencies resonate best at the base and low frequencies closer to the apex.
Phase-locking-with action potential firing locking to a specific phase of incoming sound
When an auditory stimulus reaches the cochlea what occurs to excite inner hair cells?
Potassium flows in through the open ion channels to depolarize the cell, causing a receptor potential
