Auditory Nerve

inner and outer hair cells are connected to the

auditory nerve (by hair cell bases)

can’t interpret or hear sound if

auditory nerve is damaged or dead

auditory nerve =

cranial nerve #8

stapedius muscles function is to

protect

stapedius muscle is connected to

cranial nerve #7

cranial nerve 7 and cranial nerve 8

work together

afferent =

bottom to top (sound transmission) bottom = outer ear

efferent

top to bottom, top = brain

type 1 fiber

inner hair cells signal transmission to the brain (90-95% of all fibers)

type 2 fiber

5-15% of auditory nerve fibers (outer hair cells, amplification)

physiological workload = to

sound transmission

auditory connected to apex of

cochlea

auditory nerve threshold

softest sound a person can hear

auditory nerve saturation point

loudest sound someone can hear

potassium cycles through

hair cells

in hair cells potassium generates

potentials that stimulate the neurotransmitter → auditory nerve which = action potential

condensation

stapes hits cochlea

rarefaction

stapes moves away from cochlea

depolarization

stapes away from cochlea, basilar membrane upward, hair cells away from center (rarefaction), potassium into haircell

hyperpolarization

stapes towards cochlea, basilar membrane downward, hair cells toward center (condensation), potassium moves out of hair cells

endocochlear potential

endolymph in scala media at 80 mV

intercellular resting potential

hair cells have -70 mV

potential difference across hair cells inside and out =

150 mV

depolarization of hair cells causes

the release of neurotransmitter

hyperpolarization leads to

decreased nerve firings

inner hair cells =

signal transmission

outer hair cells =

cochlear amplification

impedance mismatch

difference in fluid and air in middle ear (33dB increase)

place theory = tonotopic organization

different areas of the cochlea react to sound differently

direct current (DC)

continuous movement of BM up and down (doesn’t stop until you die)

alternating current

can changed when spooked or hearing a loud sound