T2 L12 Physiology of hearing Flashcards
What are the functions of hearing?
Altering to dangers
Localisation of objects
Recognition
Communication via speech
What are sounds?
Pressure waves that propagate through air at 340m/s
What is the equation for intensity?
dB = 10 x log (sound intensity / reference intensity) or 20 x log (sound pressure / reference pressure)
What is the range of frequencies of ideal human hearing?
20-20,000Hz
Above what intensity can lead to permanent hearing damage?
90dB
What forms the peripheral auditory system?
Outer ear
Middle ear
Cochlea
Auditory nerve
What is the function of the middle ear?
Transmit sound from outer to inner ear.
Transmits vibrations from tympani to oval window of cochlea & increases pressure by 45X
What is Ottis media?
Known as glue ear
Infection or inflammation of middle ear
What can Ottis media be caused by?
Upper respiratory tract infection
What happens if glue ear is chronic?
It can lead to conductive hearing loss
What is the treatment for glue ear?
Grommets to drain
What is otoscleorsis?
Fusion of the stapes with the oval window
What is the cochlea?
Long, coiled, fluid-filled tube
What sounds does the basal end of the cochlea detect?
High frequency sounds
What sounds does the apical end of the cochlea detect?
Low frequency sounds
How do scala vestibule and scala tympani communicate?
Via helicotrema at apex of cochlear
What areas contain perilymph?
Scala vestibular
Scala tympani
What is the composition of perilymph?
High Na+
Low K+
What areas contain endolymph?
Scala media
What is the composition of endolymph?
High K+
Low Na+
What is the function of the organ or corti?
Detect sound-induced motions of basilar membrane and convert them into electrical signals
What are the 2 types of sensory hair cells?
Inner hair cells
Outer hair cells
What are the inner hair cells innervated by?
Afferent nerve fibres
What are the outer hair cells innervated by?
Efferent nerve fibres
What membrane of the hair cells is bathed in endolymph?
Apical membrane
What membrane of the hair cells is bathed in perilymph?
Basolateral membrane
How many hair cells in each human cochlea?
15,000
Don’t regenerate
Describe mechanotransduction in hair cells
Deflection of hair bundle –> opens nonselective cation channels
K+ is the major cation in endolymph so it enters & depolarises hair cells. Ca2+ enters & causes adaption
Ca2+ triggers release of vesicles
What is the movement of K+ in endolymph driven by?
Electro-gradient
What do outer hair cells do to the basilar membrane motion?
Amplify it
What is Prestin?
Modified anion exchanger in basolateral membrane
Outer hair cell motor
What type of axons innervate an inner hair cell?
10-20 type I spiral neurons
What is the function of type I spiral neurons?
Signal reception of sound over a wide range of intensities to the brain
What type of axons innervate outer hair cell?
Type II spiral neurons
What is the function of type II spiral neurons?
Signal reception of painfully loud sound that causes cochlear damage to the brain
What do efferent fibres from medial olive innervate?
Outer hair cells
What do efferent fibres from lateral olive synapse on?
Type I afferent fibres
What can cause sensorineural hearing loss?
Noise
Ageing
Oxotoxic drugs
Genetic mutations
How can noise cause sensorineural hearing loss?
Physical effects on hair bundle structure
Mitochondrial damage, cytotoxic free radicals
Glutamate excitotoxicity
How can ageing cause sensorineural hearing loss?
Hair cells
Stria vascularis
Cochlear ganglion
What drugs are ototoxic?
Aminoglycoside antibiotics Cisplatin Loop diuretics Salicylate Solvents
What are some targets of deafness genes in the cochlea?
Tight junctions Gap junctions Afferent synapse Tectorial membrane Stria vascularis Transduction complex
What are cochlear implants?
Surgically implanted electronic device that provides sound to person who is profoundly deaf Expensive Maximum of 24 channels Speech sounds robotic music sounds awful
Where does parallel processing start?
In cochlear nucleus
What is the superior olivary complex?
2 binaural cues to localise sound in space
Where are interaural intensity differences detected?
In lateral superior olive
Where are interaural time differences detected?
Medial superior olive
What is the inferior colliculus?
Obligatory synaptic station for all afferents
Laminar organisation, iso-frequency sheets
Combines complex frequency & amplitude analysis of DCN with information on sound localisation from SOC
Encode complexity & localisation of sounds
Auditory reflex centre, reflexive orientation to stimuli
Where is the primary auditory cortex located?
Upper surface of temporal lobe
What do lesions in auditory cortex cause?
Defects in sound localisation
Discrimination of temporal pattern
Intelligibility of speech
What do lesions in Broca’s & Wernicke’s area cause?
Impair production & comprehension of speech
