Hearing and Balance

Question 1

2 components of sound

Answer 1

volume: wave amplitude
pitch: wave frequency

Question 2

3 main regions for hearing

Answer 2

external ear
middle ear
inner ear

Question 3

structures/function of external ear

Answer 3

AURICLE/PINNA
- directs sound into
EXTERNAL AUDITORY CANAL
- CERUMEN (earwax) prevents foreign objects from entering ear
TYMPANNIC MEMBRANE (eardrum)
- separates external and middle ear
- vibrates when waves reach it

Question 4

components of middle ear

Answer 4

3 AUDITORY OSSICLES
- amplify vibrations
MALLEUS (hammer)
- connected to tympanic membrane
INCUS (anvil)
STAPES

TEMPORAL BONE

• air filled
• AUDITORY TUBE connects to throat and balances pressure

Question 5

Structure + function of inner ear

Answer 5

2 connections to middle ear
OVAL WINDOW
- connects to cochlea
- stapes bangs on membrane to transmit vibrations to fluid
ROUND WINDOW
- exit point for waves in cochlea
COCHLEA
- fluid filled snail shape

VESTIBULE (static balance)
SEMICIRCULAR CANALS (kinetic balance)

VESTIBULOCOCHLEAR NERVE (XIII)
2 branches
- vistibulor
- cochlear

Question 6

difference between middle + external ear and inner ear

Answer 6

air vs fluid filled

Question 7

labyrinths in ear

Answer 7

cored out sections of temporal bone in inner ear
BONY: outside inner ear
MEMBRANOUS: inside bony, separates different fluids
- ENDOLYMPTH (high K+, low Na+). Pink
- PERILYMPTH (high Na+, low K+)
*sections different in cochlea vs semicircular canals

Question 8

end of cochlea

Answer 8

helicotrema

Question 9

3 chambers inside of cochela

Answer 9

3 chambers

1. COCHLEAR DUCT
   - endolympth
   - separates scala vestibuli
2. SCALA VESTIBULI (top, attached to oval window)
3. SCALA TYMPANI (bottom, attached to round window)
   - both filled with perilympth
   - both connected at helicotrima

Question 10

perilymph vs endolymph

Answer 10

perilympth: high Na+, low K+
endolympth: low Na+, high K+

Question 11

structures in cochlear membrane

Answer 11

• cochlear duct
• vestiular membrane (top)
• tectorial membrane
• basilar membrane (bottom)
• organ of corti (supporting cells, 3 rows outer hair cells, 3 rows inner hair cells)

Question 12

Spiral organ/organ of corti structure + function

Answer 12

Outer hair cells
- 3 rows
- regulate tension on basilar membrane

Inner hair cells
- 1 row
- interpret sound

Supporting cells

Question 13

tectorial membrane

Answer 13

• gelatanous mass that sits on top of spiral organ
• tops of hair cells embedded in membrane

Question 14

specialized receptors cells for hearing are known as

Answer 14

hair cells

Question 15

hair cell structire

Answer 15

• no axon, connected to cochlear nerve
• STERIOCILIA (mircovili on top)

Question 16

how does sound travel through ear?

Answer 16

• pinna captures sound
• tympanic membrane vibrates, moves auditory ossicles
• stapes hits on oval window
• scala vestibuli waves
• vestibular membrane vibrates
• wave to cochlear duct
• basilar membrane vibrates, moving bottom of hair cells
• bottom moves relative to top (embedded in tectorial membrane)
• bends steriocilia, creates signal

Question 17

How are loud/quiet and low/high pitch sounds differentiated

Answer 17

Tightness of basilar membrane
- tight close to oval window - can detect high pitch
- loose close to helicotrema - can detect low pitch

Volume detected by amount of hair cells stimulated

Question 18

inner ear depolarization

Answer 18

• unstimulated: gating spring relaxed
• steriocili bend towards taller steriocilia - gating spring stretches
• K+ enters cell, depolarizes
  *depolarization happens with K+ because concentration of K+ so high in endolympth compared to hair cell

Question 19

structure of microvili on hair cells

Answer 19

• arranged short to tall
• attached to each other by mechanoreceptor springs called TIP LINKS

Question 20

what happens with no round window?

Answer 20

• Waves from scala tympani have no exit
• bounce back and disrupt signals

Question 21

neural pathways for hearing

Answer 21

Cochlear nerve
Medulla oblongata
- Cochlear nuclei (can bypass)
- Superior olivary nucleus
Inferior Colliculus (midbrain)
Medial Geniculate nucleus (thalamus)
Primary Auditory Cortex (temporal lobe)

Question 22

static equilibrium and structures that govern it

Answer 22

head’s position relative to the ground
VESTIBULE
- UTRICLE: horizontal
- SACCULE: vertical

Question 23

specialized cells within utricle and saccule

Answer 23

MACULA

Question 24

Static labyrinth (how does static balance work)

Answer 24

• hair cells (MACULA) stimulated by OTOLITHIC MEMBRANE (jelly mass) weighed down by OTOLITHS
• otoliths move in response to gravity
• creates subconscious perception of balance

Question 25

dynamic labyrinth (how does kinetic balance work

Answer 25

3 semi circular canals (one in each plane)
- AMPULLAE (bulb ends) contain steriocilia that bend in response to movement
- these activate tip links

Question 26

balance neural pathway

Answer 26

vestibular nerve
vestibular nerve
- cerebellum
- motor nuclei
thalamus
- vestibular area of cortex