Lecture 17 Flashcards
How is sound generated?
Particles vibrate back and forth within a restricted area
The sound wave is travelling along the whole length
What is found with the compressed air?
many particles
What is found in rarefied air?
few particles
What is the unit of frequency?
Hz
- 1 peak per second: 1 Hz
- 1000 peaks per second 1000 Hz
What is amplitude?
Air pressure difference between peaks and troughs, expressed as decibels (dB)
What is the human hearing range?
20 - 20 000Hz
What forms the outer ear?
Pinna, auditory canal, tympanic membrane, oval window
What is the pinna?
Latin for “wing)
More sensitive to sounds from in front than behind
Convolutions of pinna play a role in sound localization in vertical direction (not horizontal)
Fixed in humans but mobile in other humans
What is the auditory canal?
Extends about 2.5cm into skull
Moves forward in through bone of the skull until it hits tympanic membrane
What is the tympanic membrane?
Vibrates backwards and forwards and causes movement in the ossicles in the middle ear
What is the oval window?
Moves backwards and forwards causing fluid movement in the cochlea
What are the ossicles of the middle ear?
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
- Malleus to incus has a rigid connection
- Incus to stapes has a flexible connection
How does the middle ear transfer sound?
Pressure spreads out on tympanic membrane to minimize sound
Pressure is concentrated in middle ear to amplify sound
How does the air to fluid transition transfer sound?
More resistance at oval window than at tympanic membrane
Must overcome resistance for sound to reach cochlea
Round window helps pressure to be relieved somewhere else
What are the inward and outward movements of the tympanic membrane called?
Inward - peak
Outward - trough
- Indent in round window retains same volume of fluid
How does the stimulus gain at the middle ear?
Ossicles amplify sounds to exert 20 times more pressure on the oval window than there is on the tympanic membrane
The oval window would barely move it if was moved directly by sound due to the air-fluid interface, as fluid has a greater inertia (impediance)
What is impedance matching?
Air and water have different inpedance?
- the tendency of each medium to oppose movement brough about by a pressure wave
How does fluid movement occur towards the base of the cochlea?
Scala vestibuli is filled with perilymph and connects at its large end to the oval window
- perilymph has high Na and low K
Scala tympani is filled with perilymph and connects at its large end to the sound window
Scala media is filled with endolymph
- High K and low Na
- Scala media is the only place where endolymph is found
- High K is crucial hearing
Stria vascularis regulates high K amounts in endolymph
Organ of corti is the organ of auditory sensory
How do hair bundles line up?
At the top of hair cells line up along cochlea
How many rows of hair cells are there in the outer hair cells and inner hair cells?
outer: 3 rows
inner: 1 row
How are inner hair cells lined up?
Primary sensory receptors
Send most of the information of sound to the brain
Are there many hair cells?
Very few in number compared to retinal cells
- very precious!
- causes hearing loss if you use inner hair cells
What two membranes cause movement of hair cells?
Tectoral membrane and basilar membrane
What are the afferent fibers that send signals to the hair cells?
Primary afferent neurons by the vestibular cochlear nerve to the auditory hair cell
