7) Hearing Flashcards
What does the oval window of the cochlea interact with?
Fluid above basilar membrane in scala vestibuli
What does the round window of the cochlea interact with?
Fluid below basilar membrane in scala tympani
What happens to hair cells when the fluid of the cochlea vibrates?
Hair cells move laterally and cilia move which cause changes in ion channels in hair cells, activating the cells and impulses are sent down cochlear nerve fibres
What is tonotopy?
Different frequencies of sound are represented at different points along the basilar membrane
Low freq = distal, high freq = proximal
How many rows of each hair cells are there?
One row of inner hair cells, three rows of outer hair cells
What are the functions of the inner and outer hair cells?
IHC = sense sounds OHC = amplifiers
How are the hair cells mechanical and electrically tuned?
Mechanically tuned by their location along the cochlea
Electrically tuned by expression of particular ion channels
What cells support and surround the hair cells?
Deiter’s cells
How does vibration in the fluid cause electrical impulse in the hair cells?
Bending of stereocilia opens mechano-transducer K+ channels causing depolarisation of hair cells. The depolarisation opens voltage gated Ca2+ channels triggering transmitter release onto spinal ganglion
What system regulates the amplification of outer hair cells?
Olivocochlear system
Where do action potentials propagate to along CN VIII?
Cochlear nucleus and auditory brainstem
What is the function of the medial superior olive?
Sound localisation by interoral time difference
What is the function of the lateral superior olive?
Sound localisation by interoral level difference
List the auditory pathway:
Cochlea -> spiral ganglion cells -> cochlear nucleus -> superior olivary complex -> inferior colliculus -> medial geniculate nucleus -> auditory cortex
Give examples of some causes of hearing impairment:
Loud noise (sound damage) Congenital Infections (rubella, glue ear) Trauma Age Ototoxicity (aminoglycosides)
How can hearing function be assessed?
Otoscopy
Audiograms
Otoacoustic emissions
Auditory brainstem response
What are otoacoustic emissions and when can they be used in testing?
Sound generated by OHC
Diasapper when inner ear is damaged
Used to test babies and children
Give examples of conductive hearing loss:
Blockage
Ruptured eardrum
Fluid accumulation
Otosclerosis
Give examples of sites damaged in sensory hearing loss:
Hair cell destruction (physical, noise related)
Hair cell death (ototoxic)
Give examples of neural hearing loss:
Spiral ganglion damage - acoustic neuroma Age related hearing loss Tinnitus Auditory neuropathy Monaural deafness
Where can congenital deafness mutations affect?
Hair cells
Tectorial membrane proteins
Non-sensory cells
Mitochondrial proteins
What are some treatments for hearing impairments?
Hearing aides
Cochlea implants
Hair cell regeneration
Cochlear nucleus implants
Describe how cochlea implants work:
Receiving unit detects sound of all frequencies and processor splits it into its different frequency components. Receiver connects to wire passed through round window into scala tympani. Has electrodes along its length that only switch on if given frequency is in sound being heard