B&B Hearing Flashcards by Lily o

What is pitch?

The single frequency we use by the brain to label the harmonic series
This is always the 1st harmonic

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True or false

Each harmonic series represents a single sound source

True

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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

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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

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Describe the shapes of:
Malleus
Incus
Stapes

Hammer
Anvil
Stirrup

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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

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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

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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

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Where does the primary auditory cortex lie?

(Heschl’s gyrus)
Lies on the superior-temporal gyrus.
It contains tonotopic maps of frequency

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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.

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What is a human’s hearing range?

20Hz - 20kHz

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What frequency are human’s most sensitive to?

2kHz

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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

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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

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What does the tensor tympanum muscle do?

Pulls the tympanic membrane

Needs to be kept under tension to transmit sound

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The stapes is inserted into an opening into the body cavity called the WHAT?

Foramen ovale

Transmits vibrations into fluid filled cochlea

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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

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What are the 3 chambers of the cochlea?

Scala vestibuli
Scala tympani
Scala media

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The floor of the scala media is the basilar membrane. What does it do?

Vibrates in a particular way when sound travels along it

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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

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What does the superior olivary nucleus do?

In the medulla
Information is compared between 2 ears
Important for localising sound in the environment

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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

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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.

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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

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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