B&B Hearing Flashcards
What is pitch?
The single frequency we use by the brain to label the harmonic series
This is always the 1st harmonic
True or false
Each harmonic series represents a single sound source
True
How can we distinguish different sources of the same sound at the same pitch?
Because of the relative strength of the individual harmonics in the series
What is the missing fundamental illusion?
An auditory illusion of pitch perception
Arises if the set of overtones or harmonics associated with a certain fundamental frequency are presented to a listener without the fundamental frequency:
the listener perceives the sound as having the pitch of the fundamental although the fundamental frequency is not present in the sound
Describe the shapes of:
Malleus
Incus
Stapes
Hammer
Anvil
Stirrup
What is impedance matching?
The air is easy to move by sound vibrations (low density) whereas fluid is very difficult to move (high density)
Role of ossicles is to make transfer from air to fluid efficient. It concentrates from large sa to small sa and is a series of levers. Concentrate force into much smaller sa.
Increases sensitivity of ear by a factor of 1000
Sound generates travelling waves that run along the basilar membrane
high frequencies reach the WHAT low frequencies run further towards the WHAT. Complex sounds are separated into their component frequencies
high - only the base
low - run towards the end
What is tonopy?
The relationship of frequency to position is seen not only on the basilar membrane but at all levels within the auditory pathways
It is maintained along the length of the auditory pathway
Where does the primary auditory cortex lie?
(Heschl’s gyrus)
Lies on the superior-temporal gyrus.
It contains tonotopic maps of frequency
The secondary auditory cortex includes Wernicke’s area, which is a centre for WHAT?
The analysis of language and is found in the dominant hemisphere.
On the opposite hemisphere, the secondary cortex is responsive to pitch changes in speech and music.
What is a human’s hearing range?
20Hz - 20kHz
What frequency are human’s most sensitive to?
2kHz
What does the pinna do?
On the external part of ear
Captures sound and bounces it into the external ear canal
This bounces it into the ear drum
Describe the process of sound moving through the ear
Pinna captures sound and bounces it into the external ear cana
Bounces it into the ear drum
Carries vibrations into middle ear (filled with air)
Here there is a pressure relief valve called the eustachian tube - goes to back of throat
Vibrations carried across air filled gap via bones called ossicles
Transmits sound into a fluid filled cavity in the inner ear - this is the cochlea
What does the tensor tympanum muscle do?
Pulls the tympanic membrane
Needs to be kept under tension to transmit sound
The stapes is inserted into an opening into the body cavity called the WHAT?
Foramen ovale
Transmits vibrations into fluid filled cochlea
What does the foramen ovale do?
Transmits vibrations into fluid filled cochlea
These vibrations can only propagate if there is a membraneous window called the foramen rotundum
What are the 3 chambers of the cochlea?
Scala vestibuli
Scala tympani
Scala media
The floor of the scala media is the basilar membrane. What does it do?
Vibrates in a particular way when sound travels along it
What is the lateral lemniscous pathway
Tract of axons in brainstem that carries information about sound from the cochlea nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain
Spatial relationship of axons remains the same
What does the superior olivary nucleus do?
In the medulla
Information is compared between 2 ears
Important for localising sound in the environment
What does the medial geniculate nucleus do?
Thalamic nucleus
All sensation (excluding olfaction) reaches the brain via the thalamus
Place where the input to the cortex can be controlled
Where does the primary auditory cortex (or Heschl’s gyrus) lie?
Superior temporal gyrus
It contains tonotopic maps of frequency
Low frequencies anterior, high freq posterior.
The secondary auditory cortex contains Wernicke’s area. What is this?
Centre for analysis of language
Found in the dominant hemisphere
On the opposite hemisphere, the secondary cortex is responsive to pitch changes in speech/music
Describe cortical processing
Poorly understood
Multiple tonotopic maps
Individual cortical columns are tuned to particular frequencies
The sharpness of this tuning may vary greatly between nerve cells
Some columns may be excited by sound from both ears while others may be inhibited
There are separate areas for mapping pitch (as opposed to frequency)
This provides the label harmonic series
The position of sound source can be localised with an accuracy of 3-10 degrees in what plane?
Horizontal plane
Localisation is achieved by comparing information arriving at the 2 ears
2 Parameters are used
What are they?
Interaural time delay
Interaural intensity differences
True or False
Interaural time delay ITL is indicative of sound reaching the head from different angles
True
eg sound coming from side of head will be delayed by around 0.6ms
Where are ITLs measured?
Superior olivary nucleus
How do receiver cells work?
Respond when AP from left and right ear reach them at the same time
Dependent on axon length
Each SON neurone (superior olivary neurone) represents a different ITL and hence angle
Interaural intensity differences works only for wavelengths that are longer between the distance between the WHAT?
Only works for low frequencies below WHAT?
ears
1500Hz
At frequencies above 1500Hz. because of the ambiguity of not knowing how many wavelengths separate the sound reaching the left and right ear, you need to use a mechanism called…?
Sound shadow
True or false
At high frequencies, the waves do not bend very well so do not wrap around the head very well. This causes sound to be louder in one ear than the other.
True
Above WHAT Hz, interaural intensity differences can localise source position
1500Hz
Where does the basement membrane lie?
The floor of the scala media
Describe the organ of corti
Sits on top of the basilar membrane Hearing organ Key organ on organ of corti are rows of hair cells Move back and forward Vital to detect sound
How do hair cells on organ of corti work
Move back and forward
Vital to detect sound
Close contact with tectorial membrane
What is the role of the tectorial membrane
Sits on top of hair cells
As basilar membrane and hair cells move up and down, pushes hair against tectorial membrane
Causes hair cells to release neurotransmitter - glutamate
Onto little dendrites on the end of neurons which sit on boney core of the cochlea
Forms a ganglion - collection of sensory cells
Called the spiral ganglion
What are hair cells held upright by?
Phalangeal cells
Presents the surface of the hair cells to the tectorial membrane
There are no AP in the hair cells they just depolarise and hyperpolarise with the movement of the WHAT?
Stereocilia
Not true cilia as no microtubule framework
As the basilar membrane moves up and down, the stereocilia move back and forward. How many outer rows of stereocilia are there usually?
How many inner rows are there?
3
1
As the sterocilia move to the highest row what happens?
Depolarise - ion channels open
As they move in opposite direction they hyperpolarise
This blocks the release of transmitter
When the hair cells release glutamate, where are they released onto?
Onto the dendrites of sensory nerve cells
Describe the outer hair cells
3 rows
12,000
Their role is a cochlea amplifier - amplify vibrations
Describe the inner hair cells
1 row 3,500 Their role is pitch determination 400 per octave and 30 per semitone - do not have very many of these hair cells Vulnerable to damage - do not grow back
How does the cochlea amplifier work?
Outer hair cells contract when they are excited by the waves passing along the basilar membrane
When they depolarise, they shorten
Bounces along the basilar membrane in phase with the wave
This increases the size of the wave on the membranez
Perilymph is found in the scala vestibuli and scala tympani. It is a saline solution so is high in what?
Sodium
eg nacl solution
Endolymph is found in the scala media. It is high in what?
Potassium
eg kcl solution
The potassium sodium exchange between the scala media and scala vestibuli/tympani takes place where?
In the stria vascularis
Produces the endolymph
True or false
It is normally expected in a neuron to have high potassium concentrations inside a cell and low concentrations outside the cell and high sodium outside and low sodium inside.
In the hair cell however, there is high potassium inside and even higher outside
True
Potassium flows in if channels are open
What are the concentrations of Na, K,, Cl in the perilymph?
And the endolymph
Peri
Na = 150mM
K = 3mM
Cl = 130mM
Origin from the CSF (Cerebrospinal fluid) and blood plasma
Endo
Na = 7mM
K = 140mM
Cl = 130mM
Origin from the stria Vascularis (has a sodium/potassium exchange pump)
The endolymph is +WHATmV compared to perilymph
+80
Called the endocochlea potential
Describe Waardenburg syndrome
The cells that control K+ ion secretion in the stria vascularis fail to migrate into the tissue during development
Leads to deafness
Because there is no endocochlea potential
What are stereocilia linked together by?
Tip links
Responsible for opening channels
When the distance between the stereocilia becomes greater, the tip links are stretched. The stretching of the membrane does what?
Opens the channels
(K+ channels)
When stereocilia move in opposite direction, channels close as gap is shorter
What is the stapedius reflex?
Involuntary muscle contraction that occurs in the middle ear in response to loud sound stimuli or when the person starts to vocalize.
When presented with an intense sound stimulus, the stapedius and tensor tympani muscles of the ossicles contract
What dB is a risk to hearing
87dB+
A rise of what dB represents a doubling of sound energy
3dB
What are the consequences of a very loud environment?
Temporary deafness Ear discomfort after exposure Sounds appear muffled Difficulty in interpreting speech Ringing or buzzing sensation in ears
What are the mechanisms of temporary and permanent threshold shifts?
Not fully understood
1) when a cell becomes very active, it requires lots of energy. Mitochondria produce lots of free radicals
. By product of ATP. - Metabolic overactivity
- This may be associated with an excessive increase in extracellular calcium
- Blood supply may not provide sufficient nutrients
- Apoptosis may result - mammalian hair cells will not regenerate
What happens when the ear is exposed to damaging noise levels
The first sign of damage is disruption of the hairs on hair cells
Longer exposure to intense sound leads to rounding up and shortening of the hairs
In the final stages, the remaining parts of the hairs fuse into a single mass
Hair cells receive feedback from the brainstem.
This arises from what?
The superior olivary nucleus
There are 2 decending pathways of the hair cells.
What are they?
1) direct synapses on outer hair cells - control of the cochlear amplifier
2) Indirect control of inner hair cell signals via nerve cells that receive hair cell input
What is the cocktail part effect?
Selective attention based on pitch and harmonic structure
