The auditory system Flashcards
What is a sound wave?
Vibrating particles passing vibrations onto the next particle
What is the peak of a sound wave?
Compressed air
What is the trough of a sound wave?
Rarefied air
What is frequency?
Number of compressed or rarefied patches of air that pass our ears each second
What is the units of frequency?
Hertz (Hz)
What is intensity?
Air pressure difference between peaks and troughs (amplitude)
What are the units of intensity?
Decibels (dB)
What kind of scale is decibels?
Logarithmic
What is the range of hearing for humans?
20 Hz to 20 000 Hz
What are the 3 main regions of the ear?
- Outer
- Middle
- Inner
What is included in the outer ear?
Pinna to the tympanic membrane
What is the tympanic membrane?
Eardrum
What is the pinna?
Part of the ear that you can see
What is included in the middle ear?
Tympanic membrane to the oval window (air filled)
What is included in the inner ear?
Cochlea
What is the function of the outer ear?
Convolutions allow for sound localisation in the vertical plane
What are the 3 smallest bones in the body?
Ossicles
What are the names of the ossicles?
- Hammer (also malleus)
- Anvil (also incus)
- Stirrup (also stapes)
Where are the ossicles located?
Between the tympanic membrane and oval window
Which ossicle is attached to the tympanic membrane?
Hammer (malleus)
Which ossicle is attached to the oval window?
Stirrup (stapes)
What is the connection like between the malleus and incus?
Rigid
What is the connection like between the incus and stapes?
Flexible
What is the purpose of the ossicles?
To concentrate the sound when it is transmitted to the cochlea
Why does the sound need to be concentrated by the ossicles?
- Cochlea is fluid-filled which has a higher impedance than air
- Without the ossicles, not enough force would be generated by the sound to cause sufficient fluid movement in the cochlea
- Ossicles overcome the impedance of the cochlear fluid
What happens when the tympanic membrane is pushed inwards?
- Malleus moves down which pushes incus forward, stapes pushes into oval window causing fluid to move through the cochlea
- Fluid pushes out through the round window
What happens when the tympanic membrane is pulled outwards?
- Malleus moves up which pulls incus backwards, stapes pulls back so oval window moves out and cochlear fluid comes towards oval window
- Round window pulls inwards
What is the apex of the cochlea?
Helicotrema
What are the 3 compartments of the cochlea?
- Scala vestibuli
- Scala media
- Scala tympani
Which direction does fluid move through the scala vestibuli?
From the oval window to the apex
Which direction does fluid move through the scala tympani?
From the apex to the round window
What is the fluid inside the scala vestibuli and scala tympani in the cochlea?
Perilymph
Which sections of the ear are filled with perilymph?
Scala vestibuli and scala tympani
What is the fluid inside the scala media?
Endolymph
Which section of the cochlea is filled with endolymph?
Scala media
What is special about endolymph?
High K+ content
What do the hair cells rest on?
Basilar membrane
What is the organ of Corti?
Auditory organ containing the basilar membrane and hair cells
What are the 2 kinds of hair cells?
Outer and inner
Which section of the basilar membrane detects high frequency sounds?
Bottom
Which section of the basilar membrane detects low frequency sounds?
Apex
Which part of the basilar membrane is stiff and narrow?
Bottom
Which part of the basilar membrane is floppy and wide?
Apex
What is the tonotopic map of the cochlea?
Base of the basilar membrane responds to high frequency sounds and the apex responds to low frequency
What is the membrane which is on top of the hair cells?
Tectorial membrane
Which hair cells transduce auditory information?
Inner hair cells
What is the structure of the stereocilia on the hair cells?
3 rows of stereo cilia in ascending size
What happens when the smaller stereocilia are pulled towards the taller stereocilia?
Hair cell depolarises
What happens to the hair cells when the stapes pulls outwards?
- Basilar membrane moves upwards
- Stereocilia pushed towards tallest one
- Hair cell depolarises
What happens when the taller stereocilia are pushed towards the smaller stereocilia?
Hair cell hyperpolarises
What happens to the hair cells when the stapes pushes inwards?
- Basilar membrane moves downwards
- Stereocilia pushed towards smallest one
- Hair cell hyperpolarises
Which section of the cochlea is the organ of Corti in?
Scala media
What is the function of inner hair cells?
Transduce sound
What connects the stereocilia?
Tip links
How does high intensity sound cause hearing loss?
Breaks tip links between stereocilia
What is the mechanoelectrical transducer channel called?
TMC1
What happens in the hair cell when the short cilia are pulled towards the tall ones?
- Pulling of the tip links opens TMC1
- K+ from endolymph enters the hair cell and causes depolarisation
- Voltage-gated Ca2+ channels open
- Ca2+ causes exocytosis of vesicles containing glutamate
- Glutamate binds to receptors on primary afferent neuron
Which neurotransmitter is used in the auditory system?
Glutamate
What happens in the hair cell when the tall cilia are pushed towards the small ones?
- TMC1 is closed
- Hair cell becomes hyperpolarised
- No Ca2+ so no glutamate released
What is the function of outer hair cells?
Amplify lower intensity sounds (quiet) by amplifying the movement of the cochlear fluid/basilar membrane
How are outer hair cells electromotile?
When hyper/depolarised they become shorter/longer