hearing and balance

pitch determinate

wavelength (frequency)

longer waves= ____ pitch

lower

____ waves= higher pitch

shorter

loudness determinate

amplitude (dB)

How many dB is the limit of hearing?

0 decibels

for every 10 decibels, the sounds will be ___x louder

10x

Human hearing range

20-20K Hz

As we age, what frequencies are lost

high frequencies

Male voice is primarily on the ____ Hz range

low

female voice is primarily on the ____ Hz range

high

auricle (pinna)

fleshy outer ear

auditory canal (external acoustic meatus)

tube that leads from auricle to eardrum
-contains guard hairs and cerumen (ear wax)

tympanic membrane

eardrum; vibrates by sound

What CNs innervate the tympanic membrane

5, 7, 9, 10

What makes up the outer ear

pinna, external auditory canal, tympanic membrane

What makes up middle ear

tympanic cavity, ossicles

What are the 3 ossicles

malleus, Incus, and Stapes

How does the middle ear equalize air pressure

mastoid cells: create buffer
eustachian tube: opens to get/release air from/to nasopharynx

What do the ossicles do

transmit vibrations from the eardrum to the oval window

how large is the tympanic cavity

2-3 mm

Why does the ear need to control volume/amplify force

air and fluid have different resistances
-the force of air vibrations must overcome the impedance of fluid resistance so you can still hear the same sound

How does the middle ear amplify sound?

-area difference between the tympanic membrane and the oval window increases pressure (F stays the same)
-ossicles act as levers
-intensity ~ pressure^2

malleus muscle and its CN

tensor tympani (CN5)

stapes muscle and CN

stapedius (CN7)

How do muscles dampen vibrations

auditory reflex

Auditory reflex

loud sounds/vocalization triggers CN5 and 7 to limit vibrations of tympanic and oval respecitively

What makes up the inner ear

vestibule, semicircular canals, cochlea

Structure of inner ear

bony labyrinth, perilymph, membranous labyrinth, endolymph

bony labyrinth

hard outercovering

perilymph

low K fluid between the labyrinths (extracellular)

membranous labyrinth

membranous barrier that partakes in signal transduction

endolymph

high K fluid in center of cochlea (intracellular)

What turns hair cells on in cochlea

sound

What turns hair cells on in vestibule

head position

What turns hair cells on in semicircular rotation

rotation

what occurs to keep scala vestibuli pressure the same when oval window pushes in

round window pushes out

organ of corti

auditory sense organ on scala media (endolymph)
-basilar membrane vibrations push hair cells into the tectorial membrane

inner hair cells of corti role

sound transducers

outer hair cells of corti role

sound amplifiers and pain

Which hair cell is attached to the tectorial membrane

outer

stereocilia

hairlike extensions on hair cells that create membrane potential by mechanically opening K gates when flexed

When do stereocilia depolarize the endolymph

when taller (open channels)

When do stereocilia hyperpolarize the endolymph

shorter (close channels)

What part of hair cell releases neurotransmitters

cell body

transduction in inner ear

-mechanically gated K channels depolarize (K in)
-activates Ca voltage-gated channels
-Ca stimulates glutamate release (excitatory) onto CN8
-Ca-gated K channels open to allow passive repolarization

2 components of frequency coding

location (place code) and firing rate (frequency code)

structure of cochlear fibers

gets wider/thicker near the apex

Where on cochlear fiber are frequencies higher

base

Where on cochlear fiber are frequencies lower

apex

frequency code

phase locking: CN8 will be stimulated in a same frequency as the sound

OHC amplification vibrations

Attachment to tectorial membrane amplifies vibrations

what happens to OHC length during depolarization

basal membrane upward shift, OHC shortening

what happens to OHC length during hyperpolarization

basal membrane downward shift, OHC lengthen

Olivocochlear fibers originate in...

superior olivary nucleus (SON)

What stimulates olivocochlear fibers

loud sounds

olivocochlear fibers functions

noise reduction
selective attention
prevent excitotoxicity

How do olivocochlear fibers fulfill their roles?

target the OHC to inhibit amplifying effects through neurotransmitters

What causes sensorineural hearing loss

-sounds over 85 dBs
-hair cell damage from excessive loudness

tinnitus

ringing in the ears

conductive deafness

impairs conduction in outer/middle ear
-use external hearing aids to amplify vibrations

sensorineural deafness

hair cell loss
-cochlear implants to stimulate auditory nerve directly

Auditory pathway

1: spiral ganglion
2:cochlear nuclei
3: inferior colliculus
4: medial geniculate (thalamus)

SON localizes sound laterally

(winner takes all)
louder stimulation will cause that side to be more excited and inhibit contralateral

SON localizes sound medially

(train station)
the difference in time between the pathways of left and right ear

consistency of otolithic membrane

jello

consistency of otoconia

sand

vestibule function

senses head orientation and linear acceleration based on gravity and linear head displacement

3 components of vestibule

maculae, utricle, saccule

maculae

house hair cells

utricle

horizontal macula
-upright sensitivity

saccule

vertical macula
-supine sensitivity

significance of striola

sensitive to all directions of tilt and amplifies signal to noise

semicircular canal function

senses head rotation based on angular acceleration

Balance pathways

1: vestibular ganglion
2: vestibular nuclei
3: VP thalamus

VOR

complementary eye movements to head movements

nystagmus

fast, corrective eye movements triggered by inappropriate VORs

What makes up balance perceptions

80% visual
15% vestibular
5% proprioception

lateral semicircular canals sensing direction

turning ("no" movement)

anterior/posterior semicircular canals sensing direction

rotating ("yes" and shoulder to ear)

anatomy of semicircular canals

cristae houses cupula which is pushed during rotation

how many axes of rotation are the semicircular canals sensitive to

1 (no striola)