Hearing - Henkel - Exam 1 Flashcards
The ear must code at least 3 characteristics of sound waves in order to represent differences in sounds:
- Frequency in cycles per second (Hz) –> ____
- Sound level in decibels (dB) –> ____
- Timing – onset, offset, duration, gaps
Location – direction and distance: these must be computed centrally, not by the ear itself
The ear must code at least 3 characteristics of sound waves in order to represent differences in sounds:
- Frequency in cycles per second (Hz) –> pitch
- Sound level in decibels (dB) –> loudness
- Timing – onset, offset, duration, gaps
Location – direction and distance: these must be computed centrally, not by the ear itself
The external ear is the pinna and the ear canal (external auditory meatus). The middle ear is a space full of ___ that is bounded by the ear drum (tympanic membrane), which is at the very end of the external ear.
The energy wave in the air strikes the ear drum. The middle ear houses three bones, which are called ossicles. They are called the __, __ and __. They are three little bones that transfer the mvmt of the ear drum and cause mvmt of the membrane interface (___ window) and act like a piston. As the ear drum moves in and out, the series of ossicle move in and out, and eventually push on the oval window which cause mvmt of fluid. The middle ear transfers the energy that is happening at the ear drum and transfers it to the oval window (air to fluid). The middle ear __ and matches the energy that initially came via air waves (remember, it has to amplify since it is entering fluid). If you fill the middle ear of something other than air, then you will have problems hearing (like if you had pus or otitis media).
In a nutshell, the external and middle ear function like a piston engine to magnify the force and timing of air waves to match the force needed to conduct the movement to fluid.
The external ear is the pinna and the ear canal (external auditory meatus). The middle ear is a space full of air that is bounded by the ear drum (tympanic membrane), which is at the very end of the external ear.
The energy wave in the air strikes the ear drum. The middle ear houses three bones, which are called ossicles. They are called the malleus, inca, stapes. They are three little bones that transfer the mvmt of the ear drum and cause mvmt of the membrane interface (oval window) and act like a piston. As the ear drum moves in and out, the series of ossicle move in and out, and eventually push on the oval window which cause mvmt of fluid. The middle ear transfers the energy that is happening at the ear drum and transfers it to the oval window (air to fluid). The middle ear amplifies and matches the energy that initially came via air waves (remember, it has to amplify since it is entering fluid). If you fill the middle ear of something other than air, then you will have problems hearing (like if you had pus or otitis media).
In a nutshell, the external and middle ear function like a piston engine to magnify the force and timing of air waves to match the force needed to conduct the movement to fluid.
Normally, the eardrum should be concaved and transparent. If it is infected, it will not transparent and it will bulge towards you.
If the function of the middle ear is to transfer and magnify sound in the conduction pathway, then if your eardrum is infected, you have ____ deafness.
Anything that intereferes with mvmt of the pressure wave from the environemt to the inner ear, will reduce the ability to conduct energy.
This is called ____ deafness. Reasons for why ths happens?
- ___ ____
- ____ ___
- _____ : affects the connection of the ossicles, so that they dont form the moving bony parts of the middle ear. Sometimes, when it is severe, the otologist can go in and replace the stapes, the ossicle that fits in the oval window (plunger part).
The main point is: anything that intereferes with conduction of the energy wave from outside to the inside, will cause a coduction deafness (a reduction of sensitiviy of the ear).
Normally, the eardrum should be concaved and transparent. If it is infected, it will not transparent and it will bulge towards you.
If the function of the middle ear is to transfer and magnify sound in the conduction pathway, then if your eardrum is infected, you have conduction deafness.
Anything that intereferes with mvmt of the pressure wave from the environemt to the inner ear, will reduce the ability to conduct energy.
This is called conduction deafness. Reasons for why ths happens?
- Otitis media
- Ear wax
- Otosclerosis : affects the connection of the ossicles, so that they dont form the moving bony parts of the middle ear. Sometimes, when it is severe, the otologist can go in and replace the stapes, the ossicle that fits in the oval window (plunger part).
The main point is: anything that intereferes with conduction of the energy wave from outside to the inside, will cause a coduction deafness (a reduction of sensitiviy of the ear).
Function of the ____: transduces mechanical energy to neural impulses that represents the parameters of the stimulus.
Function of the cochlea: transduces mechanical energy to neural impulses that represents the parameters of the stimulus.
The inner ear hair cells transduce ___ energy of fluid waves to ____ energy and auditory nerve fibers transmit the potential coded changes in membrane potential in the form action potentials the coded information to the brainstem.
The __ and __ labyrinth of the inner ear is divided into the cochlea, vestibule, and three semicircular canals. The hearing apparatus is the ___.
The spiraling, osseous labyrinth of the __ is fluid filled with ____, and encapsulates the membranous labyrinth, which is also fluid filled with ___.
Within the lining of the membranous labyrinth is an epithelial-like structure with __ __ cells.
The base of the fluid-filled osseous labyrinth is separated at one end from the middle ear by the ___ window and at the other end by the ___ window. Both windows are tight membranous structures that bulge in and out with pressure waves caused by movement of the stapes against the oval window.
The function of the cochlea is __ __. Conduction of the back and forth movement of the tympanic membrane to the fluid-filled inner ear by the ossicles activates the __ __ cells so that mechanical energy is converted to nerve activity coding precise details in the sound stimulus.
The inner ear hair cells transduce mechanical energy of fluid waves to elecochemical energy and auditory nerve fibers transmit the potential coded changes in membrane potential in the form action potentials the coded information to the brainstem.
The osseous and membranous labyrinth of the inner ear is divided into the cochlea, vestibule, and three semicircular canals. The hearing apparatus is the cochlea.
The spiraling, osseous labyrinth of the cochlea is fluid filled with perilymph, and encapsulates the membranous labyrinth, which is also fluid filled with endolymph.
Within the lining of the membranous labyrinth is an epithelial-like structure with sensory hair cells.
The base of the fluid-filled osseous labyrinth is separated at one end from the middle ear by the oval window and at the other end by the round window. Both windows are tight membranous structures that bulge in and out with pressure waves caused by movement of the stapes against the oval window.
The function of the cochlea is signal transduction. Conduction of the back and forth movement of the tympanic membrane to the fluid-filled inner ear by the ossicles activates the sensory hair cells so that mechanical energy is converted to nerve activity coding precise details in the sound stimulus.
- Like a staircase, the osseous and membranous labyrinth spiral around the bony, screw-like core of the cochlea called the ___. In the hollow of the ___ is the auditory nerve and spiral ganglion
- There are 2½ turns in the spiral of the cochlea from the base to its apex and 34mm in length if uncurled (the length is only important when considering the possible length of a cochlear implant which will be taken up below).
- Viewed in a mid-modiolar section, there are 3 fluid filled spaces: the upper chamber is scala ___; the middle chamber, scala ___ (cochlear duct); and the lower chamber, scala ___. Scala ___ and scala ___ are continuous at the apex of the spiral.
- The base of scala vestibule is continuous with the vestibule of the vestibular end organ and separated from the footplate of stapes in the middle ear by the ___window . The base of scala ___ borders the medial wall of the tympanic cavity at the round window.
- Like a staircase, the osseous and membranous labyrinth spiral around the bony, screw-like core of the cochlea called the modiolus. In the hollow of the modiolus is the auditory nerve and spiral ganglion
- There are 2½ turns in the spiral of the cochlea from the base to its apex and 34mm in length if uncurled (the length is only important when considering the possible length of a cochlear implant which will be taken up below).
- Viewed in a mid-modiolar section, there are 3 fluid filled spaces: the upper chamber is scala vestibuli; the middle chamber, scala media (cochlear duct); and the lower chamber, scala tympani. Scala vestibuli and scala tympani are continuous at the apex of the spiral.
- The base of scala vestibule is continuous with the vestibule of the vestibular end organ and separated from the footplate of stapes in the middle ear by the oval window . The base of scala tympani borders the medial wall of the tympanic cavity at the round window.
Chambers of labyrinth and organ of Corti
- A cross-section through one turn of the cochlea reveals its inner structure. The upper, scala ___ and lower, scala ___ of the osseous labyrinth surround the scala __ of the membranous labyrinth.
- The fluid filling scala vestibuli and tympani is __lymph high in ___+ similar in composition to CSF; filling scala media is __lymph, high in ___+ similar to intercellular fluid.
- ____ membrane separates scala vestibuli from scala media (cochlear duct)
- From base to apex, the basilar membrane stretches between the inner (osseous) spiral shelf of the modiolus and the outer, spiral ligament. It separates scala ___ from the ___ __
- The organ of Corti is formed by specialized epithelia in scala ___ (cochlear duct) that rest upon the basilar membrane. Three groups of epithelial cells are identified: __ __ cells, __ __ cells, and supporting cells. The apical surfaces of these cells face the fluid of the chamber.
- From the inner shelf of the cochlear duct, a stiff gelatinous structure, the ___ membrane, is suspended over the epithelia of the organ of Corti.
- There is a single, spiraling column of inner hair cells from base to apex of the cochlea; there are three parallel spiraling columns of outer hair cells. Overall there are approximately 15,000 hair cells in a healthy cochlea with a 1:3 ratio of IHCs to OHCs.
- ___ ___ is a specialized vascular area of the lateral (outer) wall of the cochlear duct that, assisted by supporting cells of the organ of Corti, maintains the fluid content of the membranous labyrinth.
- ___ disease and a variety of related disorders with both hearing and vestibular symptoms result from failure of these specialized areas and cells to maintain the proper fluid balance in the membranous labyrinth.
Chambers of labyrinth and organ of Corti
- A cross-section through one turn of the cochlea reveals its inner structure. The upper, scala vestibule and lower, scala tympani of the osseous labyrinth surround the scala media of the membranous labyrinth.
- The fluid filling scala vestibuli and tympani is perilymph high in Na+ similar in composition to CSF; filling scala media is endolymph, high in K+ similar to intercellular fluid.
- Reissner’s membrane separates scala vestibuli from scala media (cochlear duct)
- From base to apex, the basilar membrane stretches between the inner (osseous) spiral shelf of the modiolus and the outer, spiral ligament. It separates scala tympani from the scala media.
- The organ of Corti is formed by specialized epithelia in scala media (cochlear duct) that rest upon the basilar membrane. Three groups of epithelial cells are identified: inner hair cells, outer hair cells, and supporting cells. The apical surfaces of these cells face the fluid of the chamber.
- From the inner shelf of the cochlear duct, a stiff gelatinous structure, the tectorial membrane, is suspended over the epithelia of the organ of Corti.
- There is a single, spiraling column of inner hair cells from base to apex of the cochlea; there are three parallel spiraling columns of outer hair cells. Overall there are approximately 15,000 hair cells in a healthy cochlea with a 1:3 ratio of IHCs to OHCs.
- Stria vascularis is a specialized vascular area of the lateral (outer) wall of the cochlear duct that, assisted by supporting cells of the organ of Corti, maintains the fluid content of the membranous labyrinth.
- Meniere’s disease and a variety of related disorders with both hearing and vestibular symptoms result from failure of these specialized areas and cells to maintain the proper fluid balance in the membranous labyrinth.
Hair cells:
- On the apical surface of the hair cells is a bundle of ____ extending into the endolymph of the cochlear duct.
- Inner and outer hair cells are separated from one another by specialized, arched supporting cells.
- The inner hair cells (IHC) are ___-shape and have several straight rows of stereocilia on their apical surface. Each successive row of stereocilia is ____ than the preceding row. The hair bundle is thus ___, such that the tallest row is positioned on the side corresponding to the ___ wall of cochlear duct.
- The outer hair cells (OHC) are tube-shaped and have several rows of stereocilia. Again, the hair bundle of each cell is polarized with the___ row on the outer side.
- Efferent feedback pathways to the IHC and OHC provide means for central brain processes to modulate sensitivity of the cochlea.
Hair cells:
- On the apical surface of the hair cells is a bundle of stereocilia extending into the endolymph of the cochlear duct.
- Inner and outer hair cells are separated from one another by specialized, arched supporting cells.
- The inner hair cells (IHC) are goblet-shape and have several straight rows of stereocilia on their apical surface. Each successive row of stereocilia is shorter than the preceding row. The hair bundle is thus polarized, such that the tallest row is positioned on the side corresponding to the outer wall of cochlear duct.
- The outer hair cells (OHC) are tube-shaped and have several rows of stereocilia. Again, the hair bundle of each cell is polarized with the tallest row on the outer side.
- Efferent feedback pathways to the IHC and OHC provide means for central brain processes to modulate sensitivity of the cochlea.
Stereocilia:
- Fluid waves rock the basilar membrane and shear the hair bundles against the stiff, ___ membrane initiating __ transduction. Deflection toward the ____ stereocilia depolarizes the cell and in the other direction hyperpolarizes.
- Neurotransmitters are released each time the hair cell ____ thereby activating eighth nerve fibers. Discharge rate of eighth nerve fibers is directly related to features of the sound stimulus.
Stereocilia:
- Fluid waves rock the basilar membrane and shear the hair bundles against the stiff, tectorial membrane initiating signal transduction. Deflection toward the taller stereocilia depolarizes the cell and in the other direction hyperpolarizes.
- Neurotransmitters are released each time the hair cell hyperpolarizes thereby activating eighth nerve fibers. Discharge rate of eighth nerve fibers is directly related to features of the sound stimulus.
In response to sound, the __ membrane vibrates up and down, which causes the __ of __ to vibrate up and down, which causes the ___ membrane to move in a windshield wiper like fashion that causes ___ on hair cells to bend, causing a signal in the auditory nerve that then goes to the brain and tells the brain, “hey, you are hearing something!!”
What fluid is surrounding the stereocilia? What is the endolymph rich in?
How do the hair cells cause an AP?
In response to sound, the basilar membrane vibrates up and down, which causes the organ of corti to vibrate up and down, which causes the tectorial membrane to move in a windshield wiper like fashion that causes sterocilia on hair cells to bend, causing a signal in the auditory nerve that then goes to the brain and tells the brain, “hey, you are hearing something!!”
The fluid that surrounds the stereocilia is endolymph, which is very rich in K+ ions.
When the hair cells bend (towards the tallest row), it opens K+ channels on the stereocilia (depolarizes), which allows K+ from the endolymph to rush in. This increases the voltage. This increase in voltage opens Ca++ channels, and Ca++ increase, which causes release of NT’s. The NT then activates the the primary afferent of the spiral ganglia cells of CN VIII.
Cochlea:
___ frequencies are mapped at the base, and ___ frequencies are mapped at the apex. WIth age, you begin to lose hair cells first at the base because it is closest to the exposure of the sound. So with age, many people have high/low frequency hear loss first.
Cochlea:
High frequencies are mapped at the base, and low frequencies are mapped at the apex. WIth age, you begin to lose hair cells first at the base because it is clsoest to the exposure of the sound. So with age, many people have high frequency hear loss first.
There are two types of hair cells in the organ of Corti, the inner and outer hair cells. The ___ hair cells perform an amplifying role and it is the ___ hair cells that detect the sound and transmit it to the brain via the auditory nerve.
Think of a swing: if a person sitting on a swing (basilar membrane) pumps his legs (___ hair cells), the amplitude of the swing motion is increased in response to a push (sound stimulus)
There are two types of hair cells in the organ of Corti, the inner and outer hair cells. The outer hair cells(OHC) perform an amplifying role and it is the innerhair cells (IHC) that detect the sound and transmit it to the brain via the auditory nerve.
think of a swing: if a person sitting on a swing (basilar membrane) pumps his legs (OHC), the amplitude of the swing motion is increased in response to a push (sound stimulus)
___ ganglion cells will be the primary afferents in the auditory parts of CN VIII. These __ ganglion cells are synapsing at various points along the basilar membrane at the hair cells.
So, If you were to record from each spiral ganglion cell, just as an inner hair cell would be most sensitive to a very narrow range of frequency, the sprial ganglion cell that synapses there as a result of the depolarization of the inner hair cell, is also very sensitive to that range. So, as we tranduce the signal to a neural impulse, each of those gangion cells will be just as fine tuned as those inner hair cells are.
We can map freuqnecy for the inner hair cells, just we can map freuquency of the spiral ganglion.
From PPT:
Auditory nerve fibers that code features of sound and transmit that information to ascending auditory pathways are axons of spiral ganglion cells in the modiolus that synapse on IHC. Each auditory nerve fiber is tuned to a characteristic ___.The firing rate of action potentials is a function of intensity of the signal. The pattern of firing codes relevant temporal information.
Spiral ganglion cells will be the primary afferents in the auditory parts of CN VIII. These spiral ganglion cells are synapsing at various points along the basilar membrane at the hair cells.
So, If you were to record from each spiral ganglion cell, just as an inner hair cell would be most sensitive to a very narrow range of frequency, the sprial ganglion cell that synapses there as a result of the depolarization of the inner hair cell, is also very sensitive to that range. So, as we tranduce the signal to a neural impulse, each of those gangion cells will be just as fine tuned as those inner hair cells are.
We can map freuqnecy for the inner hair cells, just we can map freuquency of the spiral ganglion.
From PPT:
Auditory nerve fibers that code features of sound and transmit that information to ascending auditory pathways are axons of spiral ganglion cells in the modiolus that synapse on IHC. Each auditory nerve fiber is tuned to a characteristic frequency. The firing rate of action potentials is a function of intensity of the signal. The pattern of firing codes relevant temporal informati
____ hearing loss - when hearing loss is due to problems with the ear canal, ear drum, or middle ear and its little bones (the malleus, incus, and stapes).
___ hearing loss - when hearing loss is due to problems of the inner ear, also known as nerve-related hearing loss
Conductive hearing loss - when hearing loss is due to problems with the ear canal, ear drum, or middle ear and its little bones (the malleus, incus, and stapes).
Sensorineural hearing loss (SNHL) - when hearing loss is due to problems of the inner ear, also known as nerve-related hearing lossg
____ hearing loss is a second type of deafness. It may sometimes be referred to as nerve deafness but is more often the result of some damage to __ cells. ___ hearing loss occurs when there is damage to hair cells (or function of hair cells) or auditory nerve transmission.
This type of hearing loss is permanent.
- Hair cells are vulnerable to a number of insults from physical trauma (loud noises) to certain antibiotics (for example, Gentamycin). Aging takes its toll as well and the resulting ____ (age-related hearing loss) is a consequence of gradual hair cell loss first in the base (high frequency representation) of the cochlea.
- Damage to ___ hair cells reduces their function as a cochlear amplifier and attenuates the sensitivity of the ear. Damage to ___ hair cells interfere with fine, feature discrimination. The implications for assisted hearing devices to aid your patient are that amplifying sounds will be most effective when ___ hair cells are still preserved.
You can also have loss of conduction and SN hearing loss (mixed).
Sensorineural hearing loss is a second type of deafness. It may sometimes be referred to as nerve deafness but is more often the result of some damage to hair cells. Sensorineural hearing loss occurs when there is damage to hair cells (or function of hair cells) or auditory nerve transmission.
This type of hearing loss is permanent.
- Hair cells are vulnerable to a number of insults from physical trauma (loud noises) to certain antibiotics (for example, Gentamycin). Aging takes its toll as well and the resulting presbycusis (age-related hearing loss) is a consequence of gradual hair cell loss first in the base (high frequency representation) of the cochlea.
- Damage to outer hair cells reduces their function as a cochlear amplifier and attenuates the sensitivity of the ear. Damage to inner hair cells interfere with fine, feature discrimination. The implications for assisted hearing devices to aid your patient are that amplifying sounds will be most effective when inner hair cells are still preserved.
There is no capacity for __ of the special sensory neuroepithelium of the inner ear.
Cochlear implants have been used successfully to provide __ signals to the __ nerve.
Placement of a multiple ___ stimulating electrode in the scala __ stimulates the spiral ganglion afferents in absence of hair cell function
- There is no capacity for regeneration of the special sensory neuroepithelium of the inner ear.
- Cochlear implants have been used successfully to provide auditory-generated electrical signals to the cochlear nerve
- Placement of a multiple channel stimulating electrode in the scala tympani stimulates the spiral ganglion afferents in absence of hair cell function
How can you tell the difference between sensorineural loss and conduction loss?
Explain each test.
- Both the Weber test and the Rinne test are used clinically to differentiate a conduction deficit from a sensorineural deficit. In the Weber test , a vibrating tuning fork (best results with 512Hz) is placed at the vertex of the skull. In a patient with normal hearing, the sound (vibration) is perceived to be located in the midline, i.e., it will be heard equally in both ears. If the sound is perceived to be louder in one ear (the left ear in this example) there is either a conductive lesion in that ear or a sensorineural deficit in the opposite ear. (i.e., the right ear). That the sound would be perceived as louder in the damaged left side seems paradoxical and is not fully understood.
- The Rinne test uses a vibrating tuning fork to compare the patient’s ability to distinguish between air conduction and bone conduction. In this test the tuning fork is first placed behind the left ear in direct contact with the mastoid process of the skull . The tuning fork is then turned and placed in front of the ear. With normal hearing air conduction is louder than bone conduction. With conductive hearing loss there is a reversal with bone conduction being louder than air conduction. The findings for normal hearing and for conductive hearing loss reflect the effect of amplification by the middle ear. With a sensorineural hearing deficit both air and bone conduction are diminished. There is no reversal in loudness for bone and air conduction.
- Behavioral audiograms are used in audiology to measure sensitivity or threshold to the speech range of frequencies in comparison to normal subject.
- Threshold is the intensity level of just barely perceptible sound at the test frequency. Normal threshold is represented as __ and decreasing sensitivity is plotted by the ___ line.
- Note some of the common sound levels of common sounds that would be just perceptible with mild, moderate or severe (profound) hearing loss.
- Behavioral audiograms are used in audiology to measure sensitivity or threshold to the speech range of frequencies in comparison to normal subject.
- Threshold is the intensity level of just barely perceptible sound at the test frequency. Normal threshold is represented as 0 and decreasing sensitivity is plotted by the descending line.
- Note some of the common sound levels of common sounds that would be just perceptible with mild, moderate or severe (profound) hearing loss.
The outer ear has funnels sound to strike the ear drum. The middle ear has amplified the wave to the fluid filled inner ear. As we cause waves of fluid at different frequencies, we bend the hair bundles, which causes _+ influx and then __++ influx. This releases the __s and activate the primary ___ nerve.
The central pathway of hearing begins at the first synapse in the __ nucleus in the brainstem. The cells that are clumped together and form a ___ nucleus where that afferent input comes
So, the first nucleus that the afferent nerves will synapse in is the ___ nucleus (all of the primary afferents in the auditory part of CN ___ synapse in the here).
A timeline: E. COLI MA
From periphery to cortex (nuclei) E. COLI MA
__ ___ cells –> ___ ganglion (Type I cells) –> ___ nucleus –> __ __ nucleus –> Nuclei of __ __ –> Inferior ___ –> __ __ nucleus
Primary auditory cortex
Association areas of auditory cortex
Fiber tracts:
ATL BAA
Auditory nerve (spiral ganglion cell axons ending in the cochlear nucleus on same side) – > Trapezoid body (axons that cross from the cochlear nucleus on one side projecting to the superior olivary nucleus on the other side) –> Lateral lemniscus (axons from the cochlear nucleus and the superior olivary nucleus projecting to the inferior colliculus-these may be crossed or uncrossed. –> Brachium of the inferior colliculus (axons from the inferior colliculus projecting to the medial geniculate nucleus) –> Auditory radiations (axons from the medial geniculate nucleus projecting to the primary auditory cortex) –> Arcuate bundle (axons connecting the primary auditory cortex with the various speech association areas of cortex.
Above CN, multiple bilateral projections ensure that central damage does NOT result in unilateral (monaural) deafness.
The outer ear has funnels sound to strike the ear drum. The middle ear has amplified the wave to the fluid filled inner ear. As we cause waves of fluid at different frequencies, we bend the hair bundles, which causes K+ influx and then Ca++ influx. This releases the NTs and activate the primary afferent nerve.
The central pathway of hearing begins at the first synapse in the cochlear nucleus in the brainstem. The cells that are clumped together and form a cochlear nucleus where that afferent input comes
So, the first nucleus that the afferent nerves will synapse in is the cochlear nucleus (all of the primary afferents in the auditory part of CN VIII synapse in the here).
A timeline: E. COLI MA
From periphery to cortex:
IHC of the ear –> Spiral ganglion (Type I cells) and Cochlear nucleus –> Superior olivary nucleus –> Nuclei of lateral lemniscus –> Inferior colliculus –> Medial geniculate nucleus –> Primary auditory cortex and Association areas of auditory cortex
Fiber tracts:
ATL BRA
Auditory nerve (spiral ganglion cell axons ending in the cochlear nucleus on same side) – > Trapezoid body (axons that cross from the cochlear nucleus on one side projecting to the superior olivary nucleus on the other side) –> Lateral lemniscus (axons from the cochlear nucleus and the superior olivary nucleus projecting to the inferior colliculus-these may be crossed or uncrossed. –> Brachium of the inferior colliculus (axons from the inferior colliculus projecting to the medial geniculate nucleus) –> Auditory radiations (axons from the medial geniculate nucleus projecting to the primary auditory cortex) –> Arcuate bundle (axons connecting the primary auditory cortex with the various speech association areas of cortex.
Above CN, multiple bilateral projections ensure that central damage does NOT result in unilateral (monaural) deafness.
There are multuple pathways in the central pathway of hearing:
- (Green tract) Beginning with the projections from the ___ ganglion to the ____ nucleus, the spatial order from base to apex of the cochlea is preserved (like a keys on a piano). High frequency areas of each nucleus are connected to high frequency areas of other nuclei and low frequency areas are connected with low frequencies in a tonotopic fashion. This tonotopic order is fundamental for ___ perception.
- (Blue and Red) A second principle in auditory connections is that above the connection of the auditory nerve with the cochlear nucleus, there are multiple ____ with both crossed and uncrossed paths existing at most levels. Crossed and uncrossed fibers then synapse in the ___ ___. As a result, sensory processing in cortical and subcortical auditory areas includes information about sounds received at one, the other or both ears. This allows us to __ the sound in each ear and tell us about the ___ of the sound. This occurs at the ___ body, which is between the ___ ___. This is essentialy a crossing point/tract where the two fibers from the left and right side cross the midline.
- Once all of this information is computated, now, all three fibers (green, blue and red) ascends in a tract called the ___ ___ towards the __ ___ in the midbrain.
- The inferior colliculus now gets information from the contralateral ear as well as the ipsilateral ear. Axons coming from I.C. then project to the ___ in the auditory thalamus. This pathway travels in the ____ of the I.C.
- ___ ___ (axons from the medial geniculate nucleus), then project to the primary auditory cortex.
- Axons then connect the primary auditory cortex with the various speech association areas of cortex via __ ___.
Lesions above the __ ___, therefore, do not result in monaural deafness.
Once the pathway gets above the cochlear nucleus, a patient can have damage on left and right side, but they will not lose hearing in one ear, because they have already crossed (___ body located in between the __ __)
That is, above CN VIII, multiple bilateral projections ensure that central damage does NOT result in unilateral (monaural) deafness.
There are multuple pathways in the central pathway of hearing:
- (Green tract) Beginning with the projections from the spiral ganglion to the cochlear nucleus, the spatial order from base to apex of the cochlea is preserved (like a keys on a piano). High frequency areas of each nucleus are connected to high frequency areas of other nuclei and low frequency areas are connected with low frequencies in a tonotopic fashion. This tonotopic order is fundamental for pitch perception.
- (Blue and Red) A second principle in auditory connections is that above the connection of the auditory nerve with the cochlear nucleus, there are multiple fibers with both crossed and uncrossed paths existing at most levels. Crossed and uncrossed fibers then synapse in the superior olive. As a result, sensory processing in cortical and subcortical auditory areas includes information about sounds received at one, the other or both ears. This allows us to compare the sound in each ear and tell us about the location of the sound. This occurs at the trapezoid body, which is between the superior olives. This is essentialy a crossing point/tract where the two fibers from the left and right side cross the midline.
- Once all of this information is computated, now, all three fibers (green, blue and red) ascends in a tract called the lateral lemniscus towards the inferior colliculus in the midbrain.
- The inferior colliculus now gets information from the contralateral ear as well as the ipsilateral ear. Axons coming from I.C. then project to the MGN in the auditory thalamus. This pathway travels in the brachium of the I.C.
- Auditory radiations (axons from the medial geniculate nucleus), then project to the primary auditory cortex.
- Axons then connect the primary auditory cortex with the various speech association areas of cortex via arcuate bundles.
Lesions above the cochlear nucleus, therefore, do not result in monaural deafness.
Once the pathway gets above the cochlear nucleus, a patient can have damage on left and right side, but they will not lose hearing in one ear, because they have already crossed (trapezoid body located in between the superior olives)
That is, above CN VIII, multiple bilateral projections ensure that central damage does NOT result in unilateral (monaural) deafness.
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Where is the cochlear nucleus?
What happens if you damage the cochlear nucleus?
What happens if you have a stroke in AICA? What type of deafness would you experience?
It is the green circle.
Remember, if you damage the cochlear nucleus, you will get mono-aural hearing loss.
Note, that because of the relationship of the cochlear nuclei to the inferior cerebellar peduncle, strokes involving the vascular field of the anterior inferior cerebellar artery (AICA) may have a combination of auditory signs (monaural deafness) and cerebellar ataxia.
The auditory nerve synapses exclusively in the cochlear nucleus; the right nerve in the right nucleus, the left nerve in the left nucleus. Since all of the auditory nerve fibers project to the cochlear nucleus, damage to the nerve and damage to the cochlear nucleus have similar results – monaural deafness. Beyond the cochlear nucleus, however, central auditory processing disorders are not so clear cut and monaural deafness does not occur. So, you could damage your right side, but you’d still have bilateral hearing, since the fibers have already crossed once you are above the cochlear nucleus.
Once difference between AICA and PICA is hearing loss.
A stroke in which one **could cause monoaural hearing loss?
A stroke in AICA. This is b/c you have damaged teh cochlear nucleus.
AICA
An AICA stroke can knock out __ ___ and would cause what?
Strokes that affect the inferior colliculus do not cause a monoaural hearing loss. They cause confusion because they cannot localize the sound, pick out meaningful syllables, etc. The fibers have already crossed at this point
An AICA stroke can knock out cochlear nucleus and would cause monoaural hearing loss (hearing loss in one ear).
Strokes that affect the inferior colliculus do not cause a monoaural hearing loss. They cause confusion because they cannot localize the sound, pick out meaningful syllables, etc. The fibers have already crossed at this point
