L32 Auditory System Flashcards
how is sound generated?
by mechanical vibrations that generate pressure waves in the medium they are traveling in (Air, water etc.)
high pressure waves have a ____ number of molecules per volume
higher
low pressure waves have a ____ number of molecules per volume
low
define frequency, what are it’s units?
tone or pitch
measured in Hz (cycles per second)
what is the range of frequency that the human ear can hear?
20-20,000 Hz
define amplitude, what are it’s units?
intensity or loudness
measured in dB
normal breathing = 10 dB
jet engine = 150 dB
what are the steps involved in sound production?
- sound pressure waves enter EAM
- produce vibrations on tympanic membrane
- sound is amplified down the chain of ossicles (malleus, incus, stapes)
- final ossicle vibrates the stapes which vibrates the oval window located in the cochlea
- organ of corti in cochlea does signal transduction
- hair cells transmit signal down CN8 which is the first element of the auditory pathway
Because the tympanic membrane is ___ larger than the oval window, the force increases by ___because the area decreased by 20x (remember that F=P/A so if A↓, F↑)
20X
20X
what is the role of the chain of ossicles
act like a lever-arm which further amplifies the sound
overall, how much does the middle ear amplify the pressure force
70-100x
describe the Scala vestibuli and tympani - what are they filled with? what is the fluid composition similar to?
are continuous with each other
are filled with perilymph which has an
ionic composition that is similar to ECF
describe the Scala media- what are they filled with? Why is there a high K+ concentration in endolymph in the scala media
filled with endolymph and is high
in K+ due to secretions from the Stria Vascularis
what is the function of the basilar membrane
separates the Media from the
Tympani and supports the Organ of Corti
what is contained within the organ or corti, what is that bathed in, why is this necessary
contains the hair cells which
are bathed in the endolymph compartment and
is necessary because of the high K+ concentration needed by the hair cells for signal transduction
how do sound waves travel from the stapes to the cochlea
Movement of the stapes produces pressure on the oval window which moves the fluids within the cochlea
*This movement of fluids (not compression) is best described as traveling waves which are translated to the basilar membrane
how do sound waves travel from the stapes to the cochlea
Movement of the stapes produces pressure on the oval window which moves the fluids within the cochlea
*This movement of fluids (not compression) is best described as traveling waves which are translated to the basilar membrane
the basilar membrane acts as a _____ for sound frequencies. explain
“Place Code”
the amount of deflection of the basilar membrane is based on its mechanical properties at that particular point in the membrane
the basilar membrane acts as a _____ for sound frequencies. explain
“Place Code”
the amount of deflection of the basilar membrane is based on its mechanical properties at that particular point in the membrane
describe the base (close to oval window) of the basilar membrane? - describe, what type of frequency does it respond to?
narrow and stiff
HIGH frequencies
describe the apex (near the helicotrema) of the basilar membrane - describe, what type of frequency does it response to?
wide and floppy
LOW frequencies
define the envelope of waves?
the sum of the deflection of the basilar membrane at different stages of the travel of the wave
which as we now know exhibits variations from base to apex
what are inner hair cells responsible for
signal transduction
What do traveling waves on the basilar membrane cause a deflection of?
cilia on the hair cells that are attached to the basilar membrane
what is the role of the outer hair cells?
amplifying the deflection of the basilar
membrane and therefore amplifying the output signal
The outer hair cells have _____that cause them to _____ in the event of a depolarization
motor proteins
shorten
what happens if the shortening across many outer hair cells takes place in proper sync?
they can help push and pull the basilar membrane such that its deflection is maximized thus amplifying the outgoing signal.
what Brodmann’s area is associated with the primary auditory cortex A1? what part of the cortex does that make up?
Broadmann Area 41 and 42
comprise
the transverse temporal gyri
how is the primary auditory cortex organized - explain organization related to frequency and columns
topographical organization of A1 = tonotopic
organized by frequency sensitivity along the rostro-caudal axis
organized in columns that
are grouped according to their
pattern of input
what are the EE columns?
those that are Excited by both ears
what are the EI columns?
those that are Excited by ONE ear and Inhibited by the OTHER ear
where does the primary auditory cortex receive input from the thalamus?
in layer-4 where the thalamo-cortical fibers synapse
*identical to the other primary sensory cortex area
what is Low Frequency Sound based on? Explain
time
pressure waves from space will reach each ear at different times which is interpreted and understood to come from the given location
how is the time delay in low frequency sound detected? what is the name of the mechanism
by the binaural pathways to the superior olive (MSO)
by a mechanism known as Coincidence Detection
low frequency: what happens If the EPSP’s from each ear arrive at the superior olive at the SAME TIME (coincidence)
there will be a large signal
low frequency: what happens ifthe EPSP’s from each ear arrive at the superior
olive at DIFFERENT TIMES (no coincidence)
there will be a smaller signal
what 2 things gives the understanding of where the sound is coming from?
The timing of EPSP arrival
signal size
what is high frequency sound based on Based on?
AMPLITUDE/INTENSITY
The amplitude varies based on the ____ created by the head if the source is____ to the midline
sound shadow
lateral
The amplitude received by one ear is _____by the head causing a lower ___ and a lower ____versus the other ear who receives a signal without any dampening thus a higher signal
“dampened”
amplitude
signal
Fibers from one ear synapse?
in the ipsilateral superior olive as well as collaterals to the Trapezoid nucleus
what does the ipsilateral superior olive sends the output info to?
the cortex
where does the Trapezoid nucleus sends inhibitory fibers to?
the contralateral superior olive
the superior olive on each side has direct excitation _____and indirect inhibition from
the ____side
ipsilateral
contralateral
what does the sum of the inputs at the superior olives result in?
contralateral inhibition and ipsilateral excitation
What happens If one side starts off with an intrinsically higher intensity?
its inhibitory contralateral will
hyperpolarize the opposite superior olive
Where is the localization and mechanism of LOW FREQ
in the medial part of the superior olive, using coincidence detection
Where is the localization and mechanism of HIGH FREQ
in the lateral part of the superior olive, using interaural amplitude differences
describe weber’s test
Place the tuning fork on the forehead and see where the sound is louder, right or left?
Normally, the person should say it is equal
using weber’s test, how could you diagnose a conductive problem?
sound lateralized to the AFFECTED side (ipsilateral)
using weber’s test, how could you diagnose a sensorineural problem
sound lateralized to the UNAFFECTED side (contralateral)
describe Rinne’s test
after we know which side has a problem, the Rinne’s test will tell us what kind of problem we have
The tuning fork is placed on the mastoid process and held there until the patient no longer hears the sound as it travels thru bone
Once the patient states they no longer hear it (via bone), the fork is held in the air next to the ear
Normal→ the air conduction should last longer and is louder due to amplification mechanisms utilized in air conduction
how can you diagnose conductive hearing loss using Rinne’s test?
diminished air conduction; thus bone conduction is better and we now know that this is a problem with the conductive system and not the neurologic system
what is otosklerosis?
Fusion of the bony labyrinth (stapes to oval window) causing Conductive hearing loss of up to 40dB
what is vestibular schwannoma?
Tumor of Schwann cells in vestibular division of CN-8 causing Sensorineural hearing loss
what happens as a result of loss of hair cells?
Can also cause Sensorineural hearing loss
May be due to aging or the exposure to high frequencies (+100dB)
This loss cannot be replaced by cell division
describe cochlear implants
Consists of a microphone, electronic processor and many stimulating electrodes in the cochlea to help restore hearing
The apparatus delivers sound directly to the cochlear nerve in the event that the hair cells are damaged/lost
define conductive hearing loss
hearing loss association with interference of sound transmission in the outer or middle ear
define sensorineural hearing loss?
hearing loss associated with pathology of the cochlea or the auditory n.
how is sound characterized?
- frequency - tone/pitch
- intensity - amplitude
- point of origin
what are the 2 mechanisms of pressure amplification in the middle ear?
size difference
lever ratio of the ossicular chain
what is the first step in the sound transduction process
deflection of hair cell stereocilia
what is the second step in the sound transduction process?
opening of ion channels
what are the elements of the auditory pathway?
cerebral cortex - transverse temporal gyrus
thalamus - medial geniculate nucleus
midbrain - inferior colliculus
pons - lateral lemniscus nucleus, superior olive, trapezoid nucleus
medulla - cochlear nuclei
auditory n. (CN 8) - spiral ganglion
define conductive hearing loss
hearing loss association with interference of sound transmission in the outer or middle ear
define sensorineural hearing loss?
hearing loss associated with pathology of the cochlea or the auditory n.
how is sound characterized?
- frequency - tone/pitch
- intensity - amplitude
- point of origin
what are the 2 mechanisms of pressure amplification in the middle ear?
size difference
lever ratio of the ossicular chain
what is the first step in the sound transduction process
deflection of hair cell stereocilia
what is the second step in the sound transduction process?
opening of ion channels
what are the elements of the auditory pathway?
cerebral cortex - transverse temporal gyrus
thalamus - medial geniculate nucleus
midbrain - inferior colliculus
pons - lateral lemniscus nucleus, superior olive, trapezoid nucleus
medulla - cochlear nuclei
auditory n. (CN 8) - spiral ganglion
what is localization of low frequency sound based on?
interaural time difference
what is the localization fo high frequency sound based on
amplitude difference
