Cochlear and hearing Flashcards
What are are the 3 chambers of the cochlear and what substances do they contain?
1) Scala vestibuli
- Perilymph
2) Scala media
- Endolymph
3) Scala tympani
- Perilymph
What is the stria vascularis?
Cells which pump K+ into the endolymph in the scala media
What is the organi of corti?
Auditory sensory organ, located on the basilar membrane
What is the potential of the endolymph compared to the perilymph?
+80mV
What does the endolymph surround?
The hair bundles
What does the perilymph surround?
The cell body and the glutamate synapse onto the primary afferent neuron
What are the different parts of the organ of corti?
1) Tectorial membrane
- Above the hair cells
2) Basilar membrane
- Below the cells
3) 1 row of inner hair cells
4) 3 rows of outer hair cells
What causes the movement of the basilar membrane?
- Waves of fluid created by the stapes hitting the oval window
What do different frequencies of sound cause the basilar membrane to do?
- Maximum displacement at different regions of the membrane
- Low frequency = base (membrane is thick and stiff)
- High frequency = apex (membrane is thin and wide)
What happens to the outer hair cells when the basilar membrane moves upwards and why?
- The tip-links (which connect the hair bundles together) become stretched as the hair cells move towards the TALLEST sterocillia
- This is because the tallest sterocillia is connected to the tectorial membrane, which doesn’t move
- Positive ion channels open, depolarisation
- Na+ channels open
- Ca2+ channels open
What happens to the outer hair cells when they are activated and what does this allow?
- Activate a protein
- Causes contraction of the outer hair cells (become shorter)
- Amplifies the movement of the basilar membrane
- Inner hair cells can respond to smaller amplitudes
What causes the inner hair cells to be activated?
Fluid movement distorting the hairs
When does the basiliar membrane move upwards?
- During RAREFIED air
- Stapes moves outwards
What is in the outer ear?
- Pinna
- Auditory canal
What is in the middle ear?
- Tympanic membrane
- Ossicles (malleus, incus and stapes)
What is in the inner ear?
- Oval window and cochlear
How does sound travel to the inner ear?
- Down the auditory canal
- Causes vibration of the tympanic membrane
- Causes vibration of the ossicles
- Causes vibraion of the oval window
What is the purpose of the ossicles?
- Concentrate pressure from the tympanic membrane onto the oval window
- As going from air filled to fluid-filled, need a higher pressure to to overcome the resistance of the fluid behind the oval window
What is the connection between the malleus and incus?
Ridgid
What is the connection between the incus and stapes?
Flexible
What are alternative names for the malleus, incus and stapes?
Hammer
Anvil
Stirrup
What is the round window?
- Helps relieve the pressure in the middle ear when the stapes is pushed into the oval window
What is the oval window connected to?
The scala vestibuli
What is the round window connected to?
The scala tympani
What happens in the middle ear during compression of the wave?
- Inward movement of tympanic membrane
- Mallues and incus move upwards
- Stapes move into the oval window
- Round window open