Hearing Physiology Flashcards
What is sound?
Is the vibration of a medium and spreads out as a wave of pressure
Pressure waves dissipate as you get further away
How can we describe sounds?
- Frequency (Hz) (pitch)
- Intensity (loudness) (dB)
What range of frequencies do humans have?
20-20000 when young but this decreases when we get older
What is the pressure ratio between the quietest detectable sound and an instantly damaging sound?
1:100 trillion
How can loudness be measures?
-We plot the quietest sound that can be heard at each frequency on an audiogram (the threshold) dB SPL
But this gives hard to interpret curves
-This is corrected by referencing actual sound pressure level against hearing thresholds in young adults with normal hearing. dbHL
Is the human ear more senstive to certain frequencies?
-Yes
At different frequencies we need different ammounts of energy to hear sounds
Why do we have 2 ears?
- Allows localisation of sound in horizontal plane
- Sound carries first and louder to side it is closest to
What 2 main structures make up the outer ear?
- Pinna
- Ear canal
Describe role of pinna?
- Amplifies and filters incoming sounds
- Directional dependant filtering at certain frequencies
- Its shape is important in localisation
What do the outer ear structures combine to do?
- Increase sound pressure level by up to 20dB.
- Frequency filtering useful for sound localisation in vertical and front-back planes.
What 2 main structures make up the middle ear?
- Tympanic membrane
- Ossicles
How do ossicles of middle ear form embryologically?
- 1st branchial arch = malleus and incus
- 2nd arch = stapes
What are the 2 protective muscles in the middle ear and what do they do?
- Stapedius reflex; protects cochlea from damage from large sounds by contracting
- Tensor tympani; protects against sounds also (really it doesnt but it does for exam)
What does the 3 bone system we have allow for?
Allows for more efficient transmitting of high frequency sound.
Gives sensitivity to high frequency sounds.
What does the eustachian tube connect?
-Connects nasopharynx to the middle ear and allows air to enter and leave the middle ear
Describe role of eustachian tube?
- Allows air to enter and leave middle ear
- Closed at rest, opens during swallowing and valsalva.
- Keeps air pressure in middle ear space the same as ambient atmospheric air pressure.
- Allow stympanic membrane to vibrate
What are the main structures in the inner ear?
Cochlea
Vestibule
What are the main functions of the cochlea and vestibular apparatus?
- Cochlea; contains sensory epithelium for hearing, the organ of corti.
- Vestibular apparatus; contains sensory structures for balance and head movements
What is organ of corti?
Sensory epithelium containing auditory hair cells
Describe role of stria vascularis?
Regulates ionic and metabolic functions of scala media.
What is the basilar membrane?
The thing that vibrates and different parts vibrate better at different frequencies.
-It is stiff and light at one end and lexible and heavy at the other.
Where are stereocilia found in the hair cells?
Form bundle at apical pole of the hair cell.
What is the tallest cilium and its significance?
- Kinocilium
- When it moves away there is depolarisation
- When it moves towards there is hyperpolarisation
What do inner hair cells do?
Is a receptor that picks up vibrations of basilar membrane, it converts mechanical to electrical energy.
