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.
