Audition Flashcards
What creates sound waves?
the compression or rarefication of air molecules
What frequencies can the human ear perceive?
between 20 and 20 000 times per second
What are the three physical dimensions of sound?
- Loundness (amplitude)
- Pitch (frequency of the molecular vibrations)
- Timbre (complexity)
What determines the loudness?
- the difference of air pressure between the compressed and rarefied air
Anatomically, what is the impact of loundness?
- bigger or smaller deformation of the eac drum
What is pitch?
the frequency of the molecular vibrations (number of cycles per second)
What is timbre?
The complexity of the sound. It can be used to identify the source of the sound wave.
What are the four subdivisions of the ear?
1) outer ear
2) middle ear
3) inner ear
What is the pinna?
The outer ear
how does the sound that is funneles through the pinna reach the middle ear?
- the sound travels through the ear canal
- it makes the tympanic membrane vibrate
- the vibrations are then transferred to the middle ear
What composes the middle ear?
the ossicles
What are the three ossicles?
malleus, incus, stapes
What separates the outer and middle ear?
oval window
what composes the outer ear?
- pinna
- tympanic membrane
What is detected by the outer ear?
Variations in air pressure
What creates the movement of the ossicles?
the vibrations of the tympanic membrane
Why does the tympanic membrane vibrate instead of just keeping its new/deformed shape?
the middle ear has an air pressur almost identical to that of the outer air
What happens when the ossicles vibrate?
- Creates waves in the water that is contained in the cochlea
- the waves in the water create bends in the basilar membrane at different spots depending on the pitch
What separates the middle ear from the inner ear?
the oval window
What are the components of the inner ear?
cochlea
What is the structure of the cochlea?
Long coiled tube-like structure that contains sensory neurons. it is filled with fluid
How does the structure of the basilar membrane allow the human ear to encode the different notes?
- the tension of the membrane varies
- the membrane bends in different places depending on the frequency of the sound
Where are high-piched noises perceived in the basilar membrane?
in the end that is closest to the oval window
What occurs when the basilar membrane has to perceive low-frequency sounds?
the tip of the basilar membrane flexes in synchrony with the virbations
What are the three divisions of the cochlea?
- scala vestibuli
- scala media
- scala tympani
What is the receptive organ of the ear?
- organ of corti
where is situated the organ of corti?
inside the scala media
what composes the organ of corti?
basilar membrane, tectorial membrane and auditory hair cells sandwiched in the middle
What are auditory hair cells?
cells that transduce sound
How do the auditory hair cells perceive the vibrations caused by sound?
through their cilia
What are the different types of hair cells?
- outer hair cells
- inner hair cells
What happens when an auditory hair cell perceives vibrations?
1) pulls open ion channels
2) depolarization of the auditory hair cells
3) sends an action potential down the axon of the auditory neurons
What is the cilia of outer hair cells attached to?
tectorial membrane
where is the cell body (soma) of the outer hair
on the basilar membrane
What is the difference between inner and outer hair cells?
the cilia of the outer hair cells are physically attached to the rigid tectorial membrane, the inner hair cell’s cilia is free in the fluid of the cochlea
Which type of hair cell transmits auditory information to the brain?
inner hair cells
How are the hair cells organized?
By row
Each rov contains three outer hair cells and one inner hair cell
What is the function of outer hair cells?
- contract like muscles to adjust the sensitivity of the tectorial membrane to vibrations
- influence the sensiticity of inner hair cells to specific frequencies
- determine how much the inner hair cells will move
What happens when people have absolutely no working inner hair cells?
complete deafness
What happens when people do not have functional outer hair cells?
extremely impaired hearing
how are the cilia of hair cells connected?
by tip links
What is the point of attachment of a tip link to a cilium called?
insertional plaque
What is the transductional role of a tip link?
- every insertional plaque has an ion channel
- the amount of stretch exerted by the tip link opens the ion channel
- the ion channel depolarizes the membrane, causing an action potential
Where do low pitched sounds deform the membrane?
- tip of the basilar membrane
Where do high pitched sounds deform the membrane?
- base of the basilar membrane
What happens when human beings are exposed to noises that are too loud?
The tip links break
What happens if a person does not have tip links, or if they are broken due to loud noise exposition?
Loss of hearing (can be temporary if the tip links grow back)
Why do tip links break?
To avoid the over secretion of glutamate, which could cause excitotoxicity
What is place coding?
- Different frequencies of sound produce maximal stimulation of hair cells at different points on the basilar membrane
- The position of the most active hair cell in the cochlea indicates the fundamental frequency of the sound wave
Which frequencies are encoded by place coding?
- moderate to high frequencies
How are very low frequencies encoded?
via rate coding
What indicates the fundamental frequency of the sound wave?
The position of the most active hair cell in the cochlea
What is rate coding?
the perception of low frequency sounds depends on the rate of glutamate release from the hair cells deepest in the cochlea (furthest from the stapes)
What determines the reaction of an inner hair cell?
- the frequency of the sound (each hair cell has a specific frquency they are most sensitive to)
- the loudness/strength of the noise (the louder the better)
How does loudness correspond to the activity of hair cells?
The louder the noise is, the more hair cells are active and the more glutamate they release
How do hair cells detect timber?
Timber is perceived by assessing the precise mixture of hair cells that are active throughout the entire cochlea
What is the fundamental frequency of a sound?
lowest and most intense frequency of the wave
What is perceived as the pitch of the sound?
the fundamental frequency
What are the overtones?
sound wave frequencies that occur at integer multiples of the fundamental frequency
What results in the timber of sound?
- the sepcific mixture of fundamental frequency with overtones that different instruments emit when playing the same note
How do we identify the instrument from which a sound comes?
by analyzing the timbre of a sound and how the sound changes over time
What is the process of analyzing the complexity of a sound?
1) brain hears the complex variation of air pressure
2) brain identifies fundamental frequency
3) brain analyzes the composition of the overtones
What is the main cause of hearing problems?
deficiencies in the hair cells
What are the different components of the timber of a sound?
- overtones
- fundamental frequency
What is the goal of a cochlear implant?
Stimulate action potentials in the auditory nerve
What is the general structure of a cochlear implant?
- processor, receiver and ransmitter on the outside of the ear
- metal wiring that goes to the cochlea
- electrodes in the cochlea
What is the method of sound perception that the cochlear implant uses?
Place coding system
How do we detect the locaiton of low-pitched sounds?
By phase difference: are the ears detecting compressed air at the same time?
How do we detect the location of high-pitched sounds?
by analyzing differences in loudness between the ears
How can you use the timbre for spatial location?
- analyze how the anatomy of the ear diminishes or amplifies the wavelengths
- need experience/habit/learning
- animals move their ears
How is the auditory information split between both hemispheres?
Both sides of the brain get access to all information from both ears
What is the organization of the primary auditory cortex?
tonotopic representation
What is tonotropic representation?
- the primary auditory cortex is organized according to frequency
- different parts of the auditory cortex respond best to different frequencies
In the primary auditory cortex, where are the high frequencies?
caudal portion
In the primary auditory cortex, where are the low frequencies?
rostral portion
From the primary auditory cortex, where does the auditory information go?
In one of the two pathways that lead to the auditory association cortex
What are the two pathways that lead the information from the primary to the association auditory cortex?
posterior/dorsal pathway
anterior/ ventral pathway
What are the two parts of the auditory association cortex?
belt and parabelt regions
Where do the two streams of auditory information meet?
in the parietal cortex
Where is the primary auditory cortex?
- upper section of the temporal libe
- mostly hidden in the lateral fissure
What is the role of the posterior/dorsal stream of auditory information?
determine the source of the sound (the “where)
What is the role of the ventral/anterior stream of auditory information?
identify the “what” of the auditory stimulus
After the information leaves the cochlea, what happens?
1) travels throught the cochlear nerve
2) the axon synapses in the ventral and dorsal cochleal nuclei, where it is duplicated to be analyzed in two parallel paths in both hemispheres (medulla)
3) the info synapses in the superior olivary nuclei (medulla) (goal: locate the source of sounds)
4) the info synapses in the inferior colliculi (midbrain) (goal: localize the source of sounds)
5) the info from the inferior colliculi synapse in the medial geniculate nucleus (thalamus)
6) the info is relayed to the primary auditory cortex (temporal lobe)
7) the information is relayed to the auditory association cortex either through the ventral or dorsal pathway
Where does the dorsal pathway of auditory information lead?
parietal lobe
Where does the ventral pathway of auditory information lead?
frontal lobe
where is the analysis of the location of the sound done in the brain?
parietal lobe
where is the analysis of the identity of the sound done in the brain?
frontal lobe
What is an auditory agnosia?
an agnosia linked to the auditory association cortex
What are the effects of auditory agnosia?
- depend on the area of the association cortex that has been lesioned
What is amusia?
- inability to produce/recognize/perceive melodic music
- unable to differentiate consonant and dissonant music
- recognize/understand the emotions in music
- can converse and understand speech
Where is the auditory information duplicated?
in the medulla
Where do the “where” auditory and visual pathways meet?
in the parietal lobe
