KIN 2Y03 M22

Special Senses: Hearing & Balance

what are the components of auditory function?

• sound

• volume

• pitch

sound

the interpretation of vibrations

sound waves

bands of compressed air followed by bands with less compressed air

volume

wave amplitude

• low amp=low volume

pitch

wave frequency

• how close waves are to each other

what are the 3 portions of ear anatomy?

1. external ear

2. middle ear

3. inner ear

what is external ear composed of?

auricle/pinna

what is middle ear composed of?

1. external auditory canal

2. auditory tube

3. temporal bone

4. auditory ossicles

5. tympanic membrane

6. oval window

7. round window

what is inner ear composed of?

1. cochlea

2. semicircular canals

3. vestibule

4. cochlear nerve

5. vestibulocochlear nerve

auricle/pinna

collects sound waves from the environment and directs them to external auditory canal

external auditory canal

has ear wax

ear wax

keeps dust, insects, water, foreign objects out of ear

what is another word for ear wax

cerumen

tympanic membrane

• thin membrane that vibrates when waves reach it

• border between external ear and middle ear

what is another name for tympanic membrane?

eardrum

what are the auditory ossicles?

1. malleus

2. incus

3. stapes

malleus

physically connected to tympanic membrane

what is purpose of auditory ossicles?

amplify sound before going into inner ear

what are the connections between middle and inner ear?

• round window

• oval window

auditory (eustachian tube)

• connects middle ear to external environment (pharynx) to equalize pressure between middle ear and external auditory canal

what happens when you can’t equalize pressure in ear?

tympanic membrane won’t vibrate

• on plane, you can chew gum to openup auditory tube

round window

• acts as exit point for waves in cochlea

• no ossicles associated w/ it

oval window

stapes hits it and allows for fluid to vibrate in cochlea

cochlea

involved in hearing, deep within temporal bone

vestibulocochlear nerve

consists of:

• vestibule

• cochlear nerve

vestibule

involved in static balance, keeps head position relative to ground

cochlear nerve

involved in hearing

semicircular canals

involved in fluid/dynamic balance, when head is accelerating/deaccelerating

what cavity is external and middle ear?

air filled cavity

what cavity is inner ear?

fluid filled cavity

bony labyrinth

outside region of inner ear

membranous labyrinth

divides semicircular canals into specific patterms

what is membranous labyrinth called in semicircular canal?

dynamic or fluid labyrinth

what is membranous labyrinth filled with?

endolymph

endolymph

has high [] of K+ and low [] of Na+

• think of endolymp is inside like inside of membrane is high in K+

what is located between bony labyrinth and membranous labyrinth?

perilymph

perilymph

has low [] of K+ and high [] of Na+

helicotrema

• end of cochlea tube

• where scala vestibuli and scala tympani connect

what is scala vestibuli attached to?

oval window

what is scala tympani attached to?

round window

vestibular membrane

thin membrane that separates scala vestibuli and cochlear duct

tectorial membrane

gelatinous membrane where hair cells sit on

what is cochlear duct filled with?

• endolymph

• specialized cells that receive waves

basilar membrane

thick layer that has specialized cells

spiral organ (organ of Corti)

epithelial cells mixed with hair cells

consists of:

• supporting cells

• outer hair cells

• inner hair cells

how many rows of outer hair cell?

3

how many rows of inner hair cell?

1

inner hair cell

detects sound, perception of sound

outer hair cell

regulates tension on basilar membrane

do hair cells have axons?

no

stereocilia

bundle of microvilli on apex of hair cells

• when it tips, it creates AP

list order of sound waves in cochlear structure

sound waves→external auditory canal→tympanic membrane→maleus→incus→foot plate of stapes→oval window→ vibration of perilymph in scala vestibuli→vibration of vestibular membrane→vibration of endolymph→displacement of basilar membrane→hair cells detect

vibration of perilymph from scala vestibuli + basilar membrane→perilymph of scala tympani→round window

tip link

connects tip of each stereocilium in a hair bundle to the side of the next longer stereocilium

• are specialized mechanoreceptors

• called gating spring

list steps of depolarization in the inner ear?

1. unstimulated form- microvilli is upright, gating spring relaxed

2. stereocilia bend toward taller stereocilia, gating spring stretches

3. K+ enters the cell (NOT Na+) bcz endolymph K+ [] is so high

how is diff in pitch detected?

based on location of hair cell across basilar membrane

• high pitch-stimulates hair cells closer to oval window

• low pitch-stimulates hair cells closer to helicotrema

how is diff in volume detected?

based on number of hair cells

• high volume-stimulates more hair cells

• low volume-stimulates less hair cells

list neural pathway for hearing?

cochlear nerve→cochlear nuclei (medulla oblongata)→superior olivary nucleus (medulla oblongata)→inferior colliculus (midbrain)→medial geniculate nucleus (thalamus)→primary auditory cortex (temporal lobe)

cochlear nuclei

sensation of pitch perception

medulla oblongata

takes some signals to send back to basilar membrane to dampen loud noises

what are 2 equilibriums of balance?

1. static

2. dynamic

static equilibrium

head’s position relative to the ground

dynamic equilibrium

gives info on whether your head is accelerating or deaccelerating

what structures are in charge of static equilibrium

macula region in vestibule, static labyrinth filled with endolymph

what does macula consist of?

1. utricle

2. saccule

has hair cells + supporting cells

utricle

gathers info from horizontal plane

saccule

gathers info from verticle plane

otolith

crystallized structures that create mass weight for otolithic membrane

otolithic membrane

geltaninous membrane where hair cells are embedded- equivalent of tectorial membrane for hearing

what is the diff in stereocillia in macula vs basilar membrane

the hair cell in macula also have same microvilli from shortest to smallest BUT it has one cilia called kinocilium

what is movement of static labyrinth?

1. otoliths stimulate hair cells by moving in response to gravity- the otolith membrane acc moves

2. the membrane bends stereocilia, opening tip links

3. creates subconscious perception of where head is and you make subtle adjustments to muscles of back and neck

4. restore head to neutral position

what structure is involved in dynamic equilibrium?

ampullae of semcircular canals, dynamic/kinetic labyrinth with ducts filled w/ endolymph

what is inside ampullae?

• crista ampullaris

• cupula

crista ampullaris

act as mechanoreceptors, there are 3 in total, one in each of the 3 semicircular canals

cupula

where hair cells are embedded- equivalent of otolithic membrane and tectorial membrane

how is head movement direction detected in dynamic equilibrium?

depending on which of the 3 semicircular canals the cupula moves in

When you accelerate your head, the cupula + endolymph moves in the ______ direction to the movement of the head.

opposite

When you decelerate your head, the cupula + endolymph moves in the _______ direction as the movement.

same, movement of head ceases

what happens when fluid canals catch up with cupula

stimulation stops

what is neural pathway of balance?

vestibular nerve→vestibular nuclei (medulla oblongata)→cerebellum OR motor nuclei (control muscles of eye)→thalamus→ vestibular area of cortex (post central gyrus)

what area do sound waves first enter into a fluid?

oval window

what membrane that separates the cochlear duct from the scala tympani?

basilar membrane

what membrane that separates the cochlear duct from the scala vestibuli?

vestibular membrane