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
Q
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
A
- 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
Q
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
A
- 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
Q
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
A
- 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
Q
The peripheral auditory system - an overview
A
29
Q
Outer ear collects sounds and funnels them onto … membrane
A
Outer ear collects sounds and funnels them onto tympanic membrane
30
Q
Middle ear: transmits vibrations of tympanum to oval window of …, increases pressure …x
A
Middle ear: transmits vibrations of tympanum to oval window of cochlea, increases pressure 45x
31
Q
Cochlea: Topically organised; apical end responds to … frequencies, basal end to … frequencies
A
Cochlea: Topically organised; apical end responds to low frequencies, basal end to high frequencies
32
Q
- 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
A
- 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
Q
- 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
A
- 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
Q
- Cochlear ganglion: transmits afferent information to brain via VIIIth nerve
- Type I neurons innervate … hair cells
- Type 2 neurons innervate … hair cells
A
- 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
Q
… innervation of … synapses and outer hair cells modifies cochlear responses
A
Efferent innervation of afferent synapses and outer hair cells modifies cochlear responses
36
Q
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
A
- 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
Q
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
A
- 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
Q
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
A
- 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
Q
Targets of deafness genes in the cochlea
A
40
Q
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 …
A
- 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
Q
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
A
- 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
Q
The central auditory system
A
43
Q
The central auditory system
A
44
Q
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
A
- 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
Q
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)
A
- 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
Q
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)
A
- 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
Q
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
A
- 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
Q
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
A
- 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
Q
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
A
- 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
Q
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
A
- 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
Q
production of speech issue - lesion where?
A
brocas area
52
Q
comprehension of speech issue - lesion where?
A
Wernicke’s area
53
Q
The central auditory system - an overview
A
54
Q
Cochlear … - parallel processing starts here
A
Cochlear nucleus - parallel processing starts here
55
Q
… … complex (…C) - uses inter-aural time differences and inter-aural intensity differences for localisation
A
Superior olivary complex (SOC) - uses inter-aural time differences and inter-aural intensity differences for localisation
56
Q
… … (…) - combines spatial analysis from SOC with information from dorsal CN, and directs auditory reflexes
A
Inferior colliculus (IC) - combines spatial analysis from SOC with information from dorsal CN, and directs auditory reflexes
57
Q
… … (..) - many functions including the analysis of complex sounds (e.g. speech) and sound localisation
A
Auditory cortex (AC) - many functions including the analysis of complex sounds (e.g. speech) and sound localisation
58
Q
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
A
- 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
