6. Hearing Flashcards
What are the two properties of sound and their units for measurement?
Frequency in Hertz, volume in decibels.
Which two sound parameters does the cochlea detect?
Frequency and volume.
What is sound defined relative to?
A threshold.
What is a decibel?
Ratio of sound to the threshold sound.
What is tonotopy?
Place = frequency along the length of the linear cochlear.
What is the travelling wave theory?
Basilar membrane resonates and so mechanically amplifies sound with progressively lower frequencies along the length of the cochlea.
How many rows are there of inner and outer hair cells?
Inner - 1 row, outer - 3 rows.
What are the roles of the inner and outer hair cell rows?
Inner - sense sound, outer - serve as amplifiers.
How are the hair cells mechanically tuned?
By their location along the cochlea.
How are the hair cells electrically tuned?
Expression of particular ion channels.
How is sound energy translated to electrical energy? (Think channels opening/closing)
Bending of stereocillia (on top of hair cells) opens K+ channels. So displacement causes membrane potential. Depolarisation opens voltage gated Ca2+ channels and raised Ca2+ levels trigger transmitter release onto spiral ganglion.
What are the two types of spiral ganglion neurones?
Type 1 (95%) inner hair cell, type 2 (5%) outer hair cell - unmyelinated, efferent pathway.
What regulates amplification of sound by the outer hair cells?
Olivocochlear system - olivocochlear bundle provides efferent feedback to hair cells.
What sound produces more APs in a larger number of axons?
Louder sounds.
How is sound information transmitted to the brain?
IHC are sense organ, transmitter release triggers action potentials, these propagate into the brain along the 8th nerve, cochlear nucleus and auditory brainstem is innervated.
How is localisation of sound possible anatomically?
We have two ears.
How is localisation of sound achieved?
Interaural timing and level. The difference in arrival times between the two ears and relative amplitude of high-frequency sounds.
What is the auditory pathway from the cochlea to the auditory cortex?
Cochlear, spiral ganglion cells, cochlear nucleus, superior olivary complex, inferior colliculus, medial geniculate nucleus, auditory cortex.
What are some of the causes of hearing impairment?
Loud noises, congenital defects, infection, ototoxic compounds, trauma, age.
How can the ears and hearing be assessed?
Visual inspection with otoscope, audiograms (plot sensitivity vs frequency), otoacoustic emission (checks amplifier function of OHC), auditory brainstem response (assess generally in babies).
What can conductive hearing loss be due to?
Blockage, ruptureseardrum, fluid accumulation, otosclerosis.
What can sensory hearing loss be due to?
Hair cell destruction (physical, noise related), hair cell death (ototoxic).
What can neural hearing loss be due to?
Spiral ganglion damage (acoustic neuroma), age related hearing loss, tinnitus association, auditory neuropathy, monaural deafness.
What is tinnitus?
Phantom sound.
