neurobiology of hearing

peripheral auditory system

outer ear, middle ear, inner ear, cranial nerve viii

central auditory system

brainstem, brain

The outer ear

pinna > external auditory meatus (CANAL) > tympanic membrane (eardrum)

middle ear

tympanic membrane turns the acoustic energy into mechanical energy > ossicles > stapes (rocks in/out of oval window)

inner ear

mechanical energy changes to hydraulic energy > the waves disrupt the hair cells in the organ of corti > hydraulic energy changes to electrochemical energy.

three fluid filled areas?

scala vestibuli, scala media, scala tympani

scala vestibuli

where the hydraulic motion of the fluid starts. when it hits the round window at the end it displaces the reissner membrane

reissner membrane

inferior membrane that separates the scala vestibuli from the scala media; it can push down on the tectorial membrane (located in scala media)

basilar membrane

superior membrane that separates the scala tympani from the scala media.

where does the organ of corti sit?

on top of the basilar membrane

Inner hair cells are

bipolar

1 multiple choice option

outer hair cells are

unipolar

1 multiple choice option

perilymph fluid

high concentration of sodium, low concentration of potassium

(low mV)

Endolymph fluid

high potassium concentration and low sodium

(high mV)

perilymph is located in the

scala vestibuli and the scala tympani

endolymph is located in the

scala media

what is maintained potential called?

endocochlear potential

(125 mV)

striata vascularis

contains the ion pumps that remove sodium and discharges potassium into the endolymph

(ensures we are pulling in new potassium and removing anything that should not be in there.

rows: inner hair cell

a single row nearest to central axis of the cochlear spiral

rows: outer hair cell

three parallel rows in the region closest to the stria vascularis

hair cells do not produce an ______ potential, but they do produce a _______ potential

action, receptor

1 multiple choice option

parts of a hair cell include

stereocilia, kinocilium, and tip links

kinocilium

the taller one

stereocilia

the shorter one

stereocilia of the outer hair cells are located where?

embedded into the tectorial membrane, forming a connection between the organ of corti and the tectorial membrane

stereocilia of the inner hair cell location

floating in the endolymph underneath the tectorial membrane

what do the tip links do?

connect the stereocilia and the kinocilium.

hyperpolarization

when the kinocilium moves towards the stereocilium

(off signal)

- CLOSES MECHANICAL CHANNELS

depolarization

when the stereocilia moves towards the kinocilium

(on signal)

- OPENS MECHANICAL CHANNELS FOR K+

when the hair cells depolarize potassium rushes in and changes the hair cell from _______ to _________

negative, positive

1 multiple choice option

when the positive signal moves down the hair cell, what happens?

calcium channels open, stimulating the release of neurotransmitters (glutamate)

what do the neurotransmitters do>

stimulate nerve endings that connect to bottom of hair cells (CN VIII)

the ______ is mostly responsible for transducing acoustic inputs

IHC

1 multiple choice option

the hair cells secrete what onto the auditory nerve?

neurotransmitters (glutamate)

frequency responses to the auditory nerve are based on what

the tonotopic distribution on the basilar membrane

CN VIII is what type of neuron

1st-order neuron

what is the order of the central auditory process?

1. cochlea

2. cochlear nucleus

3. superior olivary complex

4. inferior colliculus

5. medial geniculate body

6. A1

The cochlear nucleus is....

Relay station 1, it breaks down the frequency into spectral cues (frequency, intensity, timing)

the superior olivary complex is....

relay station 2, with the medial and the lateral parts.

SOUND LOCALIZATION

the medial superior olivary complex

specializes in low-frequency hearing (which direction its coming from = how long to get there)

the lateral superior olivary complex

specializes in higher-frequency hearing

high frequencies show what?

the difference in intensity between the two ears

low frequencies show what?

differences in time delay of the signal reaching each ear.

stapedius reflex

involuntary contraction of the stapedius muscle in the middle ear to loud sounds

what is in charge of the stapedius muscle?

superior olivary nucleus

inferior colliculi

relay station 3.

- BINAURAL HEARING AND LOCALIZATION (3D)

medial geniculate body of the thalamus

relay station 4.

- relays auditory tracts to the auditory parts of the cerebral cortex

- where the 2nd order neuron meets the 3rd order neuron

auditory cortex (heschl's gyrus)

located on the surface of the superior temporal gyrus and divided into the primary auditory cortex, secondary auditory cortex, and auditory association cortices.

primary auditory cortex (A1)

highly response to pure tones.

- sensation

secondary auditory cortex (A2)

highly responsive to complex tones

- perception.

outer hair cells send what type of signals

efferent ones

sensorineural hearing loss

an inner ear hearing loss usually due to damage to the organ of corti hair cells

auditory processing disorder

difficulty processing and interpreting symbols; a dyslexia of the ears

auditory brainstem response

non-invasive electrophysiological evoked response method used routinely by clinical audiologists to objectively assess cochlear function and neural function without need for active participation by the subject

if you turn to the right, which way will the endolymph spin?

it will move in the opposite direction so it will turn left

what are the receptor potential steps in order

• neurotransmitter is released

• CN VIII fibers fire

• K+ enters the hair cell

• kinocilium is triggered

kinocilium is triggered, K+ enters the hair cell, neurotransmitter is released, CN VIII fibers fire