Auditory Systems Flashcards
What two types of vibrations are there?
Periodic (simple and complex tones) and aperiodic (noises)
What are periodic vibrations?
Compressed air molecules which continuously bump next one with sith sound, eg. stereo speakers. Vibrations travel from bumping neighbouts, not the molecules themselves. Repeating waves in periodic vibrations called simple tone have a sinusoidal curve
What type of curve does simple tone periodic vibrations have?
Sinusoidal curve
What is another word for hearing?
Audition
What are decibals?
A logarithmic scale of the amplitude of sounds
What makes complex tones different from simple tones?
COmplex tones are repeating periodic vibrations, but they are without the repeating sinusoidal curve. They have a fundamental frequency (which sets pitch for sound) and amplitude of harmonics sets the quality of sound.
What are the harmonics of sound?
Quality
What is the fundamental frequency in sound?
It sets the pitch for the sound.
What is aperiodic vibrations?
Noise, there are continuous distributions of energy across wavelengths.
What is white noise?
A type of aperiodic vibration that contains all frequencies
What is pink noise?
A aperiodic vibration that contains mid frequencies
What is brown noise?
An aperiodic vibration that contains low frequencies.
What type of sound quality do noises (aperiodic vibrations) not have?
Pitch
What property of the wave encodes pitch?
Frequency
What are the three parts of the ear?
OUter ear Middle ear (bones and muscles) Inner ear (where transduction takes place)
What do the pinna and auditory canal work to do? What are they not good at and what is the consequence of this?
Channel sound. They are not so good gathering sounds from behind pinna, which gives sound directionality.
What is conductive hearing loss?
Problem with middle ear (usually ossicles)
What are the three ossicles in order from outside to inside?
Malleus
Incus
Stapes
What does the stapes push against?
The oval window on the cochlea
What is the malleus ossicle connected to?
The tympanic membrane (eardrum)
What is the diameter of the motion back and forth of the tympanic eardrum?
The diameter of a hydrogen atom
Why doesn’t sound travel well through different mediums? What are the implications of this in the ear (and how does it overcome this?)
Impedence causes only 3% of sound amplitude to get through tympanic membrane. The middle ear overcomes impedence mismatch problem by multiplying vibrations by 24.2x, almost back to 100%
How does the middle ear overcome the impedence mismatch problem?
Surface area ration between malleus and eardrum, and stapes and oval window (18.6x greater SA). Also the lever principle where different lengths of bones which amplifies vibrations by 1.3x
In a nutshell: surface area and the lever principle
What does the eustachian tube do?
Stabilizes pressure between outer and middle ear. The tympanic membrane works best at equal pressure. Eustachian tube collapses during flight and causes tympanic membrane to bulge in
What is the tensor tympani?
The muscle attached to malleus
What is the stapedius muscle?
Contracts in response to loud noise and stiffens up ossicles so that big, low vibrations don’t make it into cochlea very well. Protects hair cells. Attached between stapes and incus. Responsible for the stapedius acoustic reflex. Takes about 50-100 msec for this reflex.
What are the round and oval window?
The oval window is what the stapes presses on and the round window is uncovered and releases extra pressure in the lower chamber. The round window pushes out when the oval window is pushed in.
What is perilymph and where is it found?
Perilymph is fluid in the scala vestibuli (upper) and scala tympani (lower) chambers. It is very sodium rich but doesn’t have much potassium, similar to CSF and may be filtrate
What connects the scala vestibuli and the scala tympani?
Helicatrema channel
What does Reissner’s membrane separate?
The scala vestibuli from the scala media
Which scala is the organ of Corti and the tectorial membrane in?
The scala media
What is endolymph and where is it found?
Endolymph is found in the scala media and is high in potassium and low in sodium
Where is the basilar membrane narrow and stiff?
At it’s base where it’s vibrated at higher frequencies
Where is the basilar membrane wide and floppy?
At its apex (end) where it vibrates well at low frequencies
What frequency vibrates the basilar membrane at the end of the base?
16 kHz
What frequency vibrates the basilar membrane at the end of the apex?
500 Hz
What is place code? (in audition)
Code for frequency for sound is based on position of basilar membrane place that responds best to frequency of stimuli
Where does transduction in audition take place?
The organ of corti
What covers the organ of corti?
The tectorial membrane
Where is the organ of corti?
In the scala media, its structure repeats itself all down the basilar membrane.
What type of hair cells have stereocilia?
Outer hair cells and inner hair cells
What is the arrangement of stereocilia in outer hair cells?
In 3 curved lines
What is the arrangement of stereocilia in inner hair cells?
1 curved line
95% of efferent nerve fibres from the cochlea to brain contact ____ hair cells
Inner hair cells.
Auditory nerve fibres connect how many hair cells? How many nerve fibres are hair cells connected to?
Nerve fibres are connected to only one hair cell each, but each hair cell can be connected to many nerve fibres.
Where is the spiral ganglion? What is it?
In the base of the cochlea, contains cell bodies of efferent nerves that go down auditory nerve
What stereocilia are not connected to the tectorial membrane?
The stereocilia of inner hair cells. Only one row of stereocilia in outer hair cells touches tectorial membrane.
How are action potentials generated by hair cells?
When hair cell stereocilia are bent by tectorial membrane, potassium flows into them, depolarizing the hair cells and causing an influx of calcium and neurotransmitter release.
True or false? Hair cell membrane potential is independent of sound pressure (amplitude)?
False. Hair cell membrane poptential is connected to sound pressure. The physical signal is translated to electrical signal and there is perfect synchrony.
Can different places on the basilar membrane be vibrated at the same time?
Yes, this is another feature of the place code.
Who is Ruggero? What did he discover?
Ruggero did an experiment and discovered the motor protein prestin on outer hair cells, which allows outer hair cells to be cochlear amplifiers and tuners of the tectorial membrane.
What does prestin do to outer hair cells?
Allows them to change shape, which causes the hair cells to shorten when excited and elongate when inhibited. This moves the basilar membrane. Shortening pulls basilar membrane up and elongating pushes the basilar membrane down. When beinding of the stereocilia causes potassium to enter the hair cell, depolarizing and triggering motor proteins to activate and shorten the hair cell/. Happens every cycle of sound and increases sensitivity and selectivity
What was Ruggero’s experiment with furosemide?
Ruggero measured the response of basilar membrane to stimuli in the presence and absence of furosemide (which inactivated prestin). He found a loss in selectivity and sensitivity when furosemide was present.
What is cochlear amplification?
Action of hair cells by tuning basilar membrane motion. If there is a problem here then there is an inability to resolve frequencies.
What is the function of the cochlea in terms of frequency?
To break sound down into component frequencies, the brain puts them back together
What determines neurotransmitter release amount in outer hair cells?
How much the cell is depolarized, ie how much the basilar membrane rises in response to how much the eardrum is moved.
What is phase locking in audition?
Cochlear neurons that fire at some part of sine wave everytime, mostly low frequencies up to 3000 Hz. IT is for melodic sound such as piano music, causes all action potentials 2 msex apart for different pitches.
What is the auditory pathway?
Signal leaves cochlea through spinal ganglion and auditory nerve fibre
Dorsal and ventral cochlear nucleus (parallel processing happens here) for both sides (no decussation yet)
Then to superior olive complex from VCN (both left and right). Superior olive has lots of nuclei in it.
Then to medial superior olive (MSO) which deals predominantly with low frequency
Then to lateral superior olive (LSO)
Then through the lateral lemniscus to inferior colliculi
Then to MGN in thalamus before being sent to auditory cortex
When does auditory information desuccate?
Half the signal desuccates when it crosses to contralateral superior olive. Though the other half goes to the ipsilateral superior olive
Which part of the superior olive is specialized for low frequencies?
The medial superior olive (MSO)
What is the name for neurons that are physically next to each other and that are most sensitive to neighbouring frequencies?
Tonotropic, Cochlear nuclei are tonotopically organized spatially
What structure in the auditory pathway is a coincidence detector?
The medial superior olive. It gets phased locked stimuli from each ear
What is the difference between the ears in time of sound travelling?
.75 msec
How does the MSO detect coincidence?
Synchrony and desynchrony in sound from each ear by using interaural phase (time) difference
What makes the MSO fire harder? Synchrony or desynchrony?
Synchrony, desynchrony causes inhibition. Therefore firing rate of MSO determines size of interaural phase difference
What does a sound shadow cause?
Interaural intensity difference
Can the LSO detect sound directionality? How?
Yes, through sound shadowing. This is an intensity dependent measure.
What is phase locking?
The consistent firing of a cell at the same phase of a sound wave
What is the duplex theory of sound localization?
Combination of:
Interaural intensity difference
Interaural time delay
The LSO tends to be more developed in animals with good _____ detection
Frequency
Is there contralateral processing of auditory information in the brain?
Yes, left brain deals with right auditory world and so forth
What property does the MSO give to sound?
Over thereness
What is the MGN?
Medial geniculate nucleus in the thalamus relays axons to the primary auditory cortex
The auditory cortex is very topographic. In the human brain, what is the range of frequencies that are tonotopically mapped onto it?
500 Hz to 16000 Hz
What will result from damage to the auditory cortex?
Loss in the abiliti to localize sounds on opposite side of damage. Pure word deafness results form bilateral damage to the auditory cortex
What is pure word deafness?
Results from bilateral damage to the primary auditory cortex. Can’t understand spoken words. Can’t determine differences between short sounds closely spaced in time. This means that the auditory cortex is for temporal processing of sounds, especially speech.
Who is Paula Tallal?
A neuroscientist who studied developmental disability to talk and hear language. Found that these kids have a problem with short sounds spaced close together. Met Merzenich and they developed therapy for disorder, called Fast ForWord, which was eventually found to be ineffective.
