(8.1) Auditory Systems Flashcards
Sound waves have a…
frequency and amplitude
What is Frequency (=pitch)?
refers to the speed of vibrations (number of vibrations per second - Hertz, Hz)
What are Rapid vibrations?
high frequency = high pitch sound
What are Slow vibrations?
low frequency = low pitch sound
What is Amplitude?
(=loudness) refers to the size of the vibrations
What are Large vibrations?
high amplitude = loud sound
What are Small vibrations?
low amplitude = quiet sound
What is Medium?
substance that surrounds objects
What is sound?
Sound is vibrations of medium (like air or water)
A sound at a single frequency is a…
pure tone
A pure tone looks like a…
sine wave
Any sound can be created by…
summing many pure tones (sine waves) at different frequencies and different amplitudes
any sound can be ‘decomposed’ (taken apart) into…
its pure tone components (component frequencies)
The auditory system works by…
taking apart sounds into their component frequencies and ‘measuring’ the amplitude of each component
What can the ear be divided into?
Divided into outer, middle, and inner
Auditory sensory neurons are located in the…
inner ear
What function does the ear have?
to amplify sound
The middle ear amplifies sounds so…
they can pass from air to water (inside the inner ear)
The eardrum (tympanic membrane) is much larger than…
the oval window, giving a proportional amplification
The ear bones (ossicles) act as levers…
by magnifying the force of vibrations
Sound makes ear drum…
vibrate
The inner ear consists of the …
cochlea (‘snail’) and the semicircular canals
What is the Semicircular canals?
part of the vestibular system
What is the cochlea?
The cochlea is a hollow spiral tube (like a snail)
The cochlea contains the…
organ of Corti - the sensory organ of hearing
The organ of Corti runs along the…
length of the cochlea
The organ of corti sit between…
It sits between the two liquid-filled tubes (scala vestibuli and scala tympani) of the cochle
What are hair cells?
Hair cells are the sensory neurons of hearing - the neurons that respond to sound vibrations
What are the two types of hair cells?
There are two types of hair cells, outer hair cells (OHCs) and inner hair cells (IHCs)
What do outer and inner haircells form?
form two sets of rows along the length of the cochle
Bending of the ‘hairs’ (stereocilia) of hair cells pulls…
filaments (strings) connecting stereocilia
- These filaments (tip links) are believed to connect mechanically to ion channels in the hair cells, opening them (like lifting a lid by a string)
- This causes the hair cells to depolarize and fire action potentials
Do hair cells respond fast?
Hair cells respond very fast - less than 10 us
Fast responding hair cells allow…
Allows hair cells to fire in synchrony with sound vibrations but only up to about 3 kHz
Different frequencies are instead coded by hair cells preferring different frequencies at…
different locations in the cochlea
What is tonotopy?
Each location along the basilar membrane is most sensitive to one sound frequency -high frequencies near base, low frequencies near tip (apex)
Different sounds cause different patterns of activity along…
the membrane
Only the inner hair cells send out…
axons, these are the neurons that respond to sound
The outer hair cells (3x as many!) instead receive…
neural input from the auditory nerve
in response to stimulation, outer hair cells can…
contract and modify stiffness of basilar membrane - allowing fine tuning of sound sensitivity (can cause tinnitus)
Hair cells are easily damaged by…
strong sounds, one cause of deafness
Cochlear implants are…
electrodes placed inside cochlea that directly stimulate auditory nerve, mimicking function of hair cells
Information travels along axons from the inner hair cells…
to join to form the auditory nerve
When information joins the auditory nerve it….
This connects the cochlea with the olive (olivary nucleus) in the brainstem
The olive is involved in…
Olive is involved in sound localisation
What passes through the MGN?
Auditory information then passes through the MGN in the thalamus to the auditory cortex
Sounds are localised by two mechanisms…
Time differences between the ears (<3 kHz) and Intensity differences between the ears (>3 kHz)
Time differences between the ears (<3 kHz) are process in…
Processed in the medial superior olive (MSO)
Intensity differences between the ears (>3 kHz) are processed in…
Processed in the lateral superior olive (LSO)
Sound information is processed in the…
primary auditory cortex, located in the superior temporal lobe
Sound localisation utilises…
Utilise differences in sound arrival
Sound information is processed in the…
primary auditory cortex, located in the superior temporal lobe
Each sound frequency is represented where?
Like in the cochlea, each sound frequency is represented in a different location - tonotopy
