6 - Overview of the Auditory system Flashcards
What is Frequency?
- Pitch
- The number of sound cycles per second activated by the mechanics of the cochlea.
What is sound intensity?
- “Loudness”
- The amplitude of the sound wave from peak to peak, achieved by the firing rate of many nerve fibres.
What is rapid onset important for?
Localising different sounds and creating a map of the auditory world around us.
Where do sound waves travel down and what is their final destination?
They travel down the outer ear to the tympanic membrane.
How do the sound waves move across the middle ear?
Via the ossicles.
What are the 3 ossicles of the ear?
The malleus, incus and the stapes.
Where are the sensory hair cells located in the ear?
The cochlea
What are the 3 compartments of the cochlea?
The Scala vestibuli, Scala media and the Scala tympani
What does the Scala media contain?
- The organ of corti which has the sensory hair cells.
- Endolymph - high potassium and now sodium
What causes high potassium levels in the Scala media?
The cells in the Stria Vascularis
What do the Scala vestibuli and Scala tympani contain?
Perilymph - Low potassium and high sodium concentration.
What are the inner hair cells?
The main sensory cells of the cochlea.
What are outer hair cells important for?
Cochlea amplification.
What is tonotopic organisation of the cochlea?
When cells at the base respond to high frequency sounds and at the apex they respond to low frequency sounds.
How is cochlear tonotopicity established?
By the basilar membrane travelling sound waves - Sound travels along chambers in the cochlea creating a wave along the basilar membrane from base to apex.
What is characteristic frequency (CF)?
The sound of one frequency causing maximal movement of the basilar membrane at one location.
How does a lower frequency wave move along the basilar membrane?
- It travels further and causes maximal movement towards the apex.
- The location of the characteristic frequency is also closer to the apex.
How does a higher frequency wave travel along the basilar membrane?
- It doesn’t travel as far and causes maximal movement towards the base.
- the location of the characteristic frequency is also closer to the base.
How are all hair cells defined?
By the stereocilia hair bundle.
What is located within the stereocilia?
- Mechanosensitive ion channels at the tips of the shorter ones.
- Mechanoelectrical transductor channels are connected to the tip links that pull the channels open.
- Voltage gated calcium ion and potassium ion channels.
What is the hair bundle bathed in?
Endolymph (The rest is in perilymph)
What happens to the inner hair cells during excitatory stimulation?
- A large deflection of the hair cells towards the taller stereocilia, which increases the tension in the tip links.
- Opens the MET channels which causes a large MET current.
- Depolarises the hair cell, potassium moves into the perilymph to help repolarise it.
What happens to the inner hair cells during inhibitory stimulation?
- A large deflection of the hair bundle back towards the shorter stereocilia.
- the tip links slacken and the MET channels close and turn off.
- The cell gets hyperpolarised below the resting potential so there is little to no neuronal activity.
What happens to the inner hair cells during sustained stimulation?
- The sustained sound moves the hair bundle back and forth at the sound frequency.
- Generates pulses of neurotransmitter activity and release.
What is electromobility?
A function that outer hair cells have which makes them shorten and lengthen with sound frequency.
What is prestin and where is it located?
The molecule that allows the cell to shorten and lengthen in response to changes in membrane potential. Its located in the membrane of outer hair cells.
