Physiology of Hearing Flashcards
1
Q
Functions of hearing
A
- Alerting to dangers
- Localising objects
- Recognition
- Communication via speech
2
Q
The nature of sound
- Sounds are travelling pressure waves that propagate through air at about 340 m/s
- Sounds have two important attributes: … (measured in Hz) and … (measured in dB SPL), which varies with the square of pressure
- dB = 10 x log (Sound intensity / reference intensity) or:
- 20 x log (sound pressure / reference pressure)
A
- Sounds are travelling pressure waves that propagate through air at about 340 m/s
- Sounds have two important attributes: frequency (measured in Hz) and intensity (measured in dB SPL), which varies with the square of pressure
- dB = 10 x log (Sound intensity / reference intensity) or:
- 20 x log (sound pressure / reference pressure)
3
Q
The range of human hearing
- Frequency range of human hearing: approximately 20-20,000 Hz
- Adults progressively lose … frequencies
- Intensity range of human hearing varies over 14 orders of magnitude
- Intensities > …db can lead to permanent hearing damage
A
- Frequency range of human hearing: approximately 20-20,000 Hz
- Adults progressively lose high frequencies
- Intensity range of human hearing varies over 14 orders of magnitude
- Intensities > 90dB can lead to permanent hearing damage
4
Q
The peripheral auditory system
- … ear, … ear, … and auditory nerve (part of the V…th cranial nerve)
A
- Outer ear, middle ear, cochlea and auditory nerve (part of the VIIIth cranial nerve)
5
Q
The peripheral auditory system
- Outer ear, … ear, … and … nerve (part of the VIIIth cranial nerve)
A
- Outer ear, middle ear, cochlea and auditory nerve (part of the VIIIth cranial nerve)
6
Q
The Middle ear
- An impendence matching device: increases pressure - …x, by the ratio of tympanic membrane and oval window areas, and to a lesser extent by the lever action of the middle ear ossicles
- Prevents sound from being reflected back from the fluid-filled …
A
- An impendence matching device: increases pressure - 45x, by the ratio of tympanic membrane and oval window areas, and to a lesser extent by the lever action of the middle ear ossicles
- Prevents sound from being reflected back from the fluid-filled cochlea
7
Q
The Middle ear
- An impendence matching device: increases … - 45x, by the ratio of tympanic membrane and oval window areas, and to a lesser extent by the lever action of the middle ear ossicles
- Prevents sound from being reflected back from the …-filled cochlea
A
- An impendence matching device: increases pressure - 45x, by the ratio of tympanic membrane and oval window areas, and to a lesser extent by the lever action of the middle ear ossicles
- Prevents sound from being reflected back from the fluid-filled cochlea
8
Q
Otitis media (& glue ear)
- Infection or inflammation of … ear
- Usually self-limiting
- Common in …
- Often from upper respiratory tract infection
- Secretory form with effusion
- ‘Glue ear’ If chronic causes a conductive … …
- May need draining - … (little opening - insert into ear drum - drain)
A
- Infection or inflammation of middle ear
- Usually self-isolating
- Common in children
- Often from upper respiratory tract infection
- Secretory form with effusion
- ‘Glue ear’ If chronic causes a conductive hearing loss
- May need draining - grommets (little opening - insert into ear drum - drain)
9
Q
Otitis media (& glue ear)
- … or … of middle ear
- Usually self-limiting
- Common in children
- Often from … … tract infection
- Secretory form with effusion
- ‘Glue ear’ If … causes a conductive hearing loss
- May need … - grommets (little opening - insert into ear drum - drain)
A
- Infection or inflammation of middle ear
- Usually self-isolating
- Common in children
- Often from upper respiratory tract infection
- Secretory form with effusion
- ‘Glue ear’ If chronic causes a conductive hearing loss
- May need draining - grommets (little opening - insert into ear drum - drain)
10
Q
Otosclerosis
A
- Fusion of staples with oval window
- Maybe why Beethoven went deaf
- Can be fixed by surgery
11
Q
Otosclerosis
A
- Fusion of staples with oval window
- Maybe why Beethoven went deaf
- Can be fixed by surgery
12
Q
The Inner ear
- Cochlea is a long, coiled, … filled tube
- Different parts of tube are tuned to different frequencies
- … end - tuned to high-frequency sound
- … end - tuned to low-frequency sounds
A
- Cochlea is a long, coiled, fluid filled tube
- Different parts of tube are tuned to different frequencies
- Basal end - tuned to high-frequency sound
- Apical end - tuned to low-frequency sounds
13
Q
The Inner ear
- Cochlea is a long, …, fluid filled tube
- Different parts of tube are tuned to different frequencies
- Basal end - tuned to …-frequency sound
- Apical end - tuned to …-frequency sounds
A
- Cochlea is a long, coiled, fluid filled tube
- Different parts of tube are tuned to different frequencies
- Basal end - tuned to high-frequency sound
- Apical end - tuned to low-frequency sounds
14
Q
Cross section of the cochlear duct
A
15
Q
Cross section of the cochlear duct
A
16
Q
Composition of the cochlear fluids
- Scala vestibuli and scala tympani contain …, a normal extracellular fluid with high Na+ and low K+
- Scala media contains …, an unusual extracellular fluid rich in K+ and low in Na+ (produced by stria vascularis), and an electrical potential of about +90mV
A
- Scala vestibuli and scala tympani contain perilymph, a normal extracellular fluid with high Na+ and low K+
- Scala media contains endolymph, an unusual extracellular fluid rich in K+ and low in Na+ (produced by stria vascularis), and an electrical potential of about +90mV
17
Q
Composition of the cochlear fluids
- Scala vestibuli and scala tympani contain perilymph, a normal extracellular fluid with high ….+ and low ….+
- Scala media contains endolymph, an unusual extracellular fluid rich in …+ and low in …+ (produced by stria vascularis), and an electrical potential of about +90mV
A
- Scala vestibuli and scala tympani contain perilymph, a normal extracellular fluid with high Na+ and low K+
- Scala media contains endolymph, an unusual extracellular fluid rich in K+ and low in Na+ (produced by stria vascularis), and an electrical potential of about +90mV
18
Q
The organ of Corti
- Detects the sound induced motions of the basilar membrane
- Contains two types of sensory hair cells, inner hair cells and outer hair cells
- Apical membrane of hair cells is bathed in …
- Basolateral membrane of hair cells is bathed in …
- Inner hair cells are innervated by afferent nerve fibres
- Outer hair cells are mainly innervated by efferent nerve fibres
- Only 15,000 hair cells in each human cochlea, not regenerated after loss
A
- Detects the sound induced motions of the basilar membrane
- Contains two types of sensory hair cells, inner hair cells and outer hair cells
- Apical membrane of hair cells is bathed in endolymph
- Basolateral membrane of hair cells is bathed in perilymph
- Inner hair cells are innervated by afferent nerve fibres
- Outer hair cells are mainly innervated by efferent nerve fibres
- Only 15,000 hair cells in each human cochlea, not regenerated after loss
19
Q
The organ of Corti
- Detects the sound induced motions of the basilar membrane
- Contains two types of sensory hair cells, inner hair cells and outer hair cells
- Apical membrane of hair cells is bathed in endolymph
- Basolateral membrane of hair cells is bathed in perilymph
- … hair cells are innervated by afferent nerve fibres
- … hair cells are mainly innervated by efferent nerve fibres
- Only 15,000 hair cells in each human cochlea, not … after loss
A
- Detects the sound induced motions of the basilar membrane
- Contains two types of sensory hair cells, inner hair cells and outer hair cells
- Apical membrane of hair cells is bathed in endolymph
- Basolateral membrane of hair cells is bathed in perilymph
- Inner hair cells are innervated by afferent nerve fibres
- Outer hair cells are mainly innervated by efferent nerve fibres
- Only 15,000 hair cells in each human cochlea, not regenerated after loss
20
Q
Inner hair cells are innervated by …. nerve fibres
Outer hair cells are mainly innervated by … nerve fibres
A
Inner hair cells are innervated by afferent nerve fibres
Outer hair cells are mainly innervated by efferent nerve fibres
21
Q
Mechanotransduction in hair cells
- Deflection of the hair … opens non-selective cation channels, the mechano-electrical transducer (MET) channels, at the lower end of the tip links, between neighbouring sterocilia (‘hairs’)
- K+, the major cation in endolymph enters and depolarises the hair cell, driven by it’s electro-(chemical) gradient [the electrical gradient is +120 to +140 mV; there is little or no chemical gradient]; Ca2+ also enters and causes adaption
- Voltage gated Ca2+ channels open, Ca2+ triggers vesicle release
- Afferent nerve fibres (Aff NE) are activated
- … hair cells are sensory, … hair cells are sensori-motor cells
A
- Deflection of the hair bundle opens non-selective cation channels, the mechano-electrical transducer (MET) channels, at the lower end of the tip links, between neighbouring sterocilia (‘hairs’)
- K+, the major cation in endolymph enters and depolarises the hair cell, driven by it’s electro-(chemical) gradient [the electrical gradient is +120 to +140 mV; there is little or no chemical gradient]; Ca2+ also enters and causes adaption
- Voltage gated Ca2+ channels open, Ca2+ triggers vesicle release
- Afferent nerve fibres (Aff NE) are activated
- Inner hair cells are sensory, outer hair cells are sensori-motor cells
22
Q
Mechanotransduction in hair cells
- Deflection of the hair bundle opens non-selective cation channels, the mechano-electrical transducer (MET) channels, at the lower end of the tip links, between neighbouring sterocilia (‘hairs’)
- …+, the major cation in endolymph enters and depolarises the hair cell, driven by it’s electro-(chemical) gradient [the electrical gradient is +120 to +140 mV; there is little or no chemical gradient]; Ca2+ also enters and causes adaption
- Voltage gated Ca2+ channels …, Ca2+ triggers vesicle release
- … nerve fibres (Aff NE) are activated
- Inner hair cells are sensory, outer hair cells are sensori-motor cells
A
- Deflection of the hair bundle opens non-selective cation channels, the mechano-electrical transducer (MET) channels, at the lower end of the tip links, between neighbouring sterocilia (‘hairs’)
- K+, the major cation in endolymph enters and depolarises the hair cell, driven by it’s electro-(chemical) gradient [the electrical gradient is +120 to +140 mV; there is little or no chemical gradient]; Ca2+ also enters and causes adaption
- Voltage gated Ca2+ channels open, Ca2+ triggers vesicle release
- Afferent nerve fibres (Aff NE) are activated
- Inner hair cells are sensory, outer hair cells are sensori-motor cells
23
Q
Electromotility of outer hair cells
- Outer hair cells amplify … membrane motion
- … - shorten: … - lengthen
- Prestin, a modified anion exchanger in the basolateral membrane, is the OHC motor
A
- Outer hair cells amplify basilar membrane motion
- Depolarise - shorten: hyperpolarise - lengthen
- Prestin, a modified anion exchanger in the basolateral membrane, is the OHC motor
24
Q
Electromotility of outer hair cells
- Outer hair cells amplify … membrane motion
- Depolarise - …: hyperpolarise - …
- …, a modified anion exchanger in the basolateral membrane, is the OHC motor
A
- Outer hair cells amplify basilar membrane motion
- Depolarise - shorten: hyperpolarise - lengthen
- Prestin, a modified anion exchanger in the basolateral membrane, is the OHC motor
25
_Afferent innervation of the Cochlea_
* Neurons in cochlear (spiral) ganglion innervate hair cells and project axons to the brain via the ... branch of the VIIIth nerve
* Each ... hair cell is innervated by axons from 10-20 type I spiral neurons that signal the reception of sound over a wide range of intensities to the brain
* ... hair cells are innervated by type II spinal neurons that signal the reception of painfully loud sound that causes cochlear damage to the brain
* Neurons in cochlear (spiral) ganglion innervate hair cells and project axons to the brain via the auditory branch of the VIIIth nerve
* Each inner hair cell is innervated by axons from 10-20 type I spiral neurons that signal the reception of sound over a wide range of intensities to the brain
* Outer hair cells are innervated by type II spinal neurons that signal the reception of painfully loud sound that causes cochlear damage to the brain
26
_Efferent innervation of the Cochlea_
* Efferent fibres from the ... olive innervate the outer hair cells directly
* Efferent fibres from the ... olive synapse on the Type I afferent fibres
* Activation of efferent system modifies the sensitivity of the cochlea
* Efferent fibres from the medial olive innervate the outer hair cells directly
* Efferent fibres from the lateral olive synapse on the Type I afferent fibres
* Activation of efferent system modifies the sensitivity of the cochlea
27
_Efferent innervation of the Cochlea_
* Efferent fibres from the medial olive innervate the outer hair cells directly
* Efferent fibres from the lateral olive synapse on the Type I afferent fibres
* Activation of ... system modifies the ... of the cochlea
* Efferent fibres from the medial olive innervate the outer hair cells directly
* Efferent fibres from the lateral olive synapse on the Type I afferent fibres
* Activation of efferent system modifies the sensitivity of the cochlea
28
_The peripheral auditory system - an overview_
29
Outer ear collects sounds and funnels them onto ... membrane
Outer ear collects sounds and funnels them onto tympanic membrane
30
Middle ear: transmits vibrations of tympanum to oval window of ..., increases pressure ...x
Middle ear: transmits vibrations of tympanum to oval window of cochlea, increases pressure 45x
31
Cochlea: Topically organised; apical end responds to ... frequencies, basal end to ... frequencies
Cochlea: Topically organised; apical end responds to low frequencies, basal end to high frequencies
32
* Organ of Corti - contains sensory hair cells that detect vibrations of the basilar membrane and convert them into electrical signals
* Inner hair cells are purely ...
* Outer hair cells are ..., amplify ... membrane motion
* Organ of Corti - contains sensory hair cells that detect vibrations of the basilar membrane and convert them into electrical signals
* Inner hair cells are purely sensory
* Outer hair cells are sensorimotor, amplify basilar membrane motion
33
* Organ of Corti - contains sensory hair cells that detect vibrations of the basilar membrane and convert them into electrical signals
* Inner hair cells are purely sensory
* Outer hair cells are sensorimotor, amplify basilar membrane motion
* Organ of Corti - contains sensory hair cells that detect vibrations of the basilar membrane and convert them into electrical signals
* Inner hair cells are purely sensory
* Outer hair cells are sensorimotor, amplify basilar membrane motion
34
* Cochlear ganglion: transmits afferent information to brain via VIIIth nerve
* Type I neurons innervate ... hair cells
* Type 2 neurons innervate ... hair cells
* Cochlear ganglion: transmits afferent information to brain via VIIIth nerve
* Type I neurons innervate inner hair cells
* Type 2 neurons innervate outer hair cells
35
... innervation of ... synapses and outer hair cells modifies cochlear responses
Efferent innervation of afferent synapses and outer hair cells modifies cochlear responses
36
_Sensorineural hearing loss_
* ...
* Physical effects on hair bundle structure
* Mitochondrial damage, cytotoxic free radicals
* Glutamate excitotoxicity
* ... (presbyacusis)
* 30% of population over age of 70 have significant hearing loss
* Hair cells, stria vascularis, cochlear ganglion
* ... drugs
* Aminoglycoside antibiotics, cisplatin, loop diuretics, salicylate, solvents
* ... mutations
* High frequency, 1:2000 of live births, syndromic and non-syndromic, \>50 deafness genes identified, 80 additional loci, -50% of congenital deafness caused by mutations in gap junction genes
* Noise
* Physical effects on hair bundle structure
* Mitochondrial damage, cytotoxic free radicals
* Glutamate excitotoxicity
* Ageing (presbyacusis)
* 30% of population over age of 70 have significant hearing loss
* Hair cells, stria vascularis, cochlear ganglion
* Ototoxic drugs
* Aminoglycoside antibiotics, cisplatin, loop diuretics, salicylate, solvents
* Genetic mutations
* High frequency, 1:2000 of live births, syndromic and non-syndromic, \>50 deafness genes identified, 80 additional loci, -50% of congenital deafness caused by mutations in gap junction genes
37
_Sensorineural hearing loss_
* Noise
* Physical effects on ... ... structure
* Mitochondrial damage, cytotoxic free radicals
* ... excitotoxicity
* Ageing (presbyacusis)
* ...% of population over age of 70 have significant hearing loss
* Hair cells, stria vascularis, cochlear ganglion
* ... drugs
* Aminoglycoside antibiotics, cisplatin, loop diuretics, salicylate, solvents
* Genetic mutations
* High frequency, 1:... of live births, syndromic and non-syndromic, \>50 deafness genes identified, 80 additional loci, -50% of congenital deafness caused by mutations in gap junction genes
* Noise
* Physical effects on hair bundle structure
* Mitochondrial damage, cytotoxic free radicals
* Glutamate excitotoxicity
* Ageing (presbyacusis)
* 30% of population over age of 70 have significant hearing loss
* Hair cells, stria vascularis, cochlear ganglion
* Ototoxic drugs
* Aminoglycoside antibiotics, cisplatin, loop diuretics, salicylate, solvents
* Genetic mutations
* High frequency, 1:2000 of live births, syndromic and non-syndromic, \>50 deafness genes identified, 80 additional loci, -50% of congenital deafness caused by mutations in gap junction genes
38
_Sensorineural hearing loss_
* Noise
* Physical effects on hair bundle structure
* Mitochondrial damage, cytotoxic free radicals
* Glutamate ...
* Ageing (presbyacusis)
* 30% of population over age of ... have significant hearing loss
* Hair cells, stria vascularis, cochlear ganglion
* Ototoxic drugs
* Aminoglycoside antibiotics, cisplatin, loop diuretics, salicylate, solvents
* Genetic mutations
* High frequency, 1:2000 of live births, syndromic and non-syndromic, \>50 deafness genes identified, 80 additional loci, -...% of congenital deafness caused by mutations in gap junction genes
* Noise
* Physical effects on hair bundle structure
* Mitochondrial damage, cytotoxic free radicals
* Glutamate excitotoxicity
* Ageing (presbyacusis)
* 30% of population over age of 70 have significant hearing loss
* Hair cells, stria vascularis, cochlear ganglion
* Ototoxic drugs
* Aminoglycoside antibiotics, cisplatin, loop diuretics, salicylate, solvents
* Genetic mutations
* High frequency, 1:2000 of live births, syndromic and non-syndromic, \>50 deafness genes identified, 80 additional loci, -50% of congenital deafness caused by mutations in gap junction genes
39
_Targets of deafness genes in the cochlea_
40
_Cochlear Implants_
* Surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf
* ... - limited to the western world
* Results often good enough to recognise and comprehend speech
* Maximum 24 channels to substitute for 15,000 hair cells
* Speech is reported to sound '...'
* Music sounds ...
* Surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf
* Expensive - limited to the western world
* Results often good enough to recognise and comprehend speech
* Maximum 24 channels to substitute for 15,000 hair cells
* Speech is reported to sound 'robotic'
* Music sounds awful
41
_Cochlear Implants_
* Surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf
* Expensive - limited to the western world
* Results often good enough to recognise and comprehend ...
* Maximum 24 channels to substitute for ... hair cells
* Speech is reported to sound 'robotic'
* ... sounds awful
* Surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf
* Expensive - limited to the western world
* Results often good enough to recognise and comprehend speech
* Maximum 24 channels to substitute for 15,000 hair cells
* Speech is reported to sound 'robotic'
* Music sounds awful
42
_The central auditory system_
43
_The central auditory system_
44
_The cochlear nucleus_
* Parallel processing starts in cochlear nucleus
* Auditory nerve fibres from cochlear ganglion innervate many types of neuron
* Neurons extract information about level, ... and ... of sounds
* Parallel processing starts in cochlear nucleus
* Auditory nerve fibres from cochlear ganglion innervate many types of neuron
* Neurons extract information about level, onset and timing of sounds
45
_The superior olivary complex_
* Two binaural cues are used to localize sounds in space
* Interaural level differences are detected in the ... superior olive (LSO)
* Interaural time differences are detected in the ... superior olive (MSO)
* Two binaural cues are used to localize sounds in space
* Interaural level differences are detected in the lateral superior olive (LSO)
* Interaural time differences are detected in the medial superior olive (MSO)
46
_The superior olivary complex_
* Two binaural cues are used to localize sounds in space
* Interaural ... differences are detected in the lateral superior olive (LSO)
* Interaural ... differences are detected in the medial superior olive (MSO)
* Two binaural cues are used to localize sounds in space
* Interaural level differences are detected in the lateral superior olive (LSO)
* Interaural time differences are detected in the medial superior olive (MSO)
47
_The inferior colliculus_
* Obligatory synaptic station for all ...
* ... organisation in ICC, iso-frequency sheets
* Combines complex frequency and amplitude analysis of DCN with information on sound localization from SOC
* May encode complexity and localization of sounds
* Auditory reflex centre; reflexive orientation to stimuli
* Obligatory synaptic station for all afferents
* Laminar organisation in ICC, iso-frequency sheets
* Combines complex frequency and amplitude analysis of DCN with information on sound localization from SOC
* May encode complexity and localization of sounds
* Auditory reflex centre; reflexive orientation to stimuli
48
_The inferior colliculus_
* Obligatory synaptic station for all afferents
* Laminar organisation in ICC, iso-frequency sheets
* Combines complex frequency and amplitude analysis of DCN with information on sound localization from SOC
* May encode ... and ... of sounds
* Auditory ... centre; reflexive orientation to stimuli
* Obligatory synaptic station for all afferents
* Laminar organisation in ICC, iso-frequency sheets
* Combines complex frequency and amplitude analysis of DCN with information on sound localization from SOC
* May encode complexity and localization of sounds
* Auditory reflex centre; reflexive orientation to stimuli
49
_The auditory cortex_
* Primary auditory cortex is located on upper surface of ... lobe
* Lesions in auditory cortex cause defects in: sound localisation, discrimination of temporal pattern, ... of speech
* Lesions in Broca's (... aphasia) and Wernicke's (... aphasia) areas also impair the production and comprehension of speech
* Primary auditory cortex is located on supper surface of temporal lobe
* Lesions in auditory cortex cause defects in: sound localisation, discrimination of temporal pattern, intelligibility of speech
* Lesions in Broca's (motor aphasia) and Wernicke's (sensory aphasia) areas also impair the production and comprehension of speech
50
_The auditory cortex_
* Primary auditory cortex is located on upper surface of ... lobe
* Lesions in auditory cortex cause defects in: sound localisation, discrimination of temporal pattern, ... of speech
* Lesions in ... (motor aphasia) and ... (sensory aphasia) areas also impair the production and comprehension of speech
* Primary auditory cortex is located on supper surface of temporal lobe
* Lesions in auditory cortex cause defects in: sound localisation, discrimination of temporal pattern, intelligibility of speech
* Lesions in Broca's (motor aphasia) and Wernicke's (sensory aphasia) areas also impair the production and comprehension of speech
51
production of speech issue - lesion where?
brocas area
52
comprehension of speech issue - lesion where?
Wernicke's area
53
_The central auditory system - an overview_
54
Cochlear ... - parallel processing starts here
Cochlear nucleus - parallel processing starts here
55
... ... complex (...C) - uses inter-aural time differences and inter-aural intensity differences for localisation
Superior olivary complex (SOC) - uses inter-aural time differences and inter-aural intensity differences for localisation
56
... ... (...) - combines spatial analysis from SOC with information from dorsal CN, and directs auditory reflexes
Inferior colliculus (IC) - combines spatial analysis from SOC with information from dorsal CN, and directs auditory reflexes
57
... ... (..) - many functions including the analysis of complex sounds (e.g. speech) and sound localisation
Auditory cortex (AC) - many functions including the analysis of complex sounds (e.g. speech) and sound localisation
58
_Summary of key content: (Physiology of hearing)_
* Sound transmission through the outer and middle ear
* The structure and mechanics of the inner ear
* Sound transduction by hair cells
* Central auditory pathways and auditory cortex
* Learning outcomes - at the end of this lecture students should be able to
* Describe the structure and functions of the different parts of the auditory system
* Demonstrate a basic understanding of how defects along the auditory pathways cause hearing loss
* Sound transmission through the outer and middle ear
* The structure and mechanics of the inner ear
* Sound transduction by hair cells
* Central auditory pathways and auditory cortex
* Learning outcomes - at the end of this lecture students should be able to
* Describe the structure and functions of the different parts of the auditory system
* Demonstrate a basic understanding of how defects along the auditory pathways cause hearing loss
