Auditory system Flashcards
What is Sound?
The physical properties of sound wave
What is the ear?
Hardware that collects the sound
What is sensory transduction?
Conversion of sound to neural activity
What is hearing for?
- Language
- Music
- Aware of the environment
- Echo-location and navigation
- Communication
- Vigilance
What is sound?
A wave which is created by vibrating objects and propagated through a medium from one location to another
What are examples of a medium?
- Air
- Water
- Mole
What are the roles of sound/?
- Time variant pressure
- Space variant pressure
From sound source to your ears
What are periods of high pressure called?
Compressions
What are contrast with periods of low pressure called?
Rarefaction
What is Rarefaction?
Reduction of an item’s density
How do you measure amplitude?
Compare maximum and minimum pressure
What are sound amplitude associated with?
Loudness
What is the frequency of the sound?
How many cycles are there in one second (5 Hz)
What is period/cycle?
Time it takes to move from one position of wave to the next position
The higher the frequency
The higher the pitch of the sound
The faster it is oscillating
Define phase
Describes the relative position on a wave, whether you are in a peak, trough or somewhere in between
What is a pure tone?
Simplest sort of wave that can be understood
A steady sound without overtone
Sine wave
Oscillates up and down
e.g. whistling, birdsong, simple musical instrument
Sine wave shape is unchanged by linear time-invariant system
What is a complex wave?
A wave made up of a series of sound wave
What is fourier analysis?
Take complex wave and describe it as the sum of sinusoid with different frequencies and different amplitudes
What is the basis of Fourier analysis?
The ability to describe any sound of the world
Broken down into different sine components
What do different frequencies have?
Different amplitudes
What is a spectra?
Reveals information about sound waves
What are peaks in the spectrum called?
Harmonics
Occur at integer multiples of fundamental frequency pitch 0
What does fundamental frequency determine?
Pitch
What is the shape of envelope associated with?
Timbre of instrument
What is timbre?
Allows ear to distinguish sounds which have same pitch and loudness
Relates to instrument identity
What are spectrograms?
visual representation of the spectrum of frequencies of a signal as it varies with time
What are formants?
each of several prominent bands of frequency that determine the phonetic quality of a vowel.
Frequency shaping of the signal from focal folds by the vocal tract
What do movement of format change?
Identity of sound
What are real environments?
Spectro-temporally complex and individual sound sources are hard to isolate
What is found on the outer ear?
- Pinna
Visible part of the ear (Auricle) - special helical shape
What are the shape of the ears designed to do?
Collect sound from the environment and funnel it into the ear canal (External auditory meatus)
What does the outer ear do?
Conduct vibration through sround to ear (Tympanic membrane)
What is tympanic membrane?
Membrane that seals the air canal and vibrates in response to sound energy
What is present in the middle ear?
Eustachian tube
What is the Eustachian tube?
Tube that connects ears to nose and mouth
What is the consequence of swallowing?
Open the Eustachian Tube
What are the components of the Ear bones (ossicles)?
- Hammer = Malleus
- Anvil = Incus
- Stirrup = Stapes
What is the function of the ear bone?
Impedance matching
What does the ear bone allow us to do?
Take tympanic membrane with a large surface area, Collect a lot of sound energy and apply that to a much lower surface area called the oval window
What does Stapes have?
Smaller surface area - Allow us to match impedance property of inner and outer ear
What are ear muscles connected to?
- Stapedius
2. Tensor tympani
What do ear muscles control?
Movement of ear bone and gain of ear bone
What does the inner ear consist of?
- Semicircular canal (vestibular)
2. Cochlear (hearing)
What causes Basilar membrane to move up and down?
The movement of ear bone and oval window
What does the position of movement of basilar membrane depend on?
Frequency of sound
High pitch sound
Maximum movement at the base of cochlea
When does the position of maximum movement change.?
As sounds get lower in frequency
What is the displacement of basilar membrane?
Frequency dependent
What do low frequency sound cause?
Displacement at apex of cochlea
What do high frequency sound cause?
Displacement at the base of cochlea
What is Tonotopicity?
Relationship between place and frequency
Biological version of Fourier Analysis
Take any complex sound and decompose it into a pattern of movement on basilar membrane
What is place code?
Where the membrane vibrates, tells you what frequency the sound was
What creates a tonotopic representation of sound along basilar membrane?
Relationship between frequency and membrane
Detecting displacement
Filling
no. of different cells - Outer hair cells and Inner hair cells
What do inner hair cells detect?
Movement of basilar membrane caused by sound
What is sensory transduction?
Conversion of mechanical energy in sound waves to electrochemical energy in neural activity
What is each hair of hair cell called?
Stereocilium
What do each stereocilium have?
Mechanosensitive cation channels
placed on top of each membrane
How are each channel linked to the adjacent stereocilium?
Physical structures called Tip Link
What are the stages of hair bundle?
- Movement of hair bundle by sound
- Cation (K+) into hair cells
- Depolarisation of hair cells
- Synaptic vesicle release
What do stereocilia detect?
Displacement of basilar membrane
What are present in the base of hair cells?
Dendrites of auditory nerve fibres
pathway that lead to the brain
What are synaptic ribbons?
Specialised structures in the hair cells that allow communication of nerve fibres very quickly
What do synaptic ribbons detect?
very rapid signal
Sound are very fast
What are auditory system specialised for?
Speed
Where are the signal about sound encoded in?
Action potential of neurons
What do each auditory nerve fibre take in?
Frequency dependence of basilar membrane
What do outer hair cells do?
Amplify quiet sounds
Autoacoustic commission
Diagnosing hearing loss in young children that can’t talk
What are the components of the ascending pathway?
- Cochlear nucleus
- Superior Olivary complex
- Inferior colliculus
- Medial Geniculate body
- Auditory cortex
What is the function of medial geniculate body?
Control centre to filter out signal that are going to cortex
Where is auditory cortex located?
Superior Temporal gyrus
What are 3 parts of auditory cortex in humans?
- Primary (core) - Heschl’s Gyrus - BA41
- Secondary (Belt) - lateral surface of brain
- Tertiary (para-belt)
What are the roles of descending auditory pathway?
- Predictive coding
- Attentional modulation
- Gain control
What is predictive coding?
Minimize responses to expected sounds
What is attentional modulation?
Enhance coding of interesting sounds
What is Gain control?
Optimize auditory processing for current circumstances
Hearing loss
- Conductive
- Sensorineural
- Central
What are examples of Hearing Dysfunction?
- Tinnitus
- Hyperacusis
- Auditory hallucinations
- Auditory processing disorder
What are examples of recovering auditory function?
- Hearing aids - amplify sound level in ear canal
- Grommets - Allow fluid to escape middle ear
- Brain stimulation - suppress tinnitus - electrode on cortex
- Cochlea implant - Stimulate auditory nerve
