Hearing and Balance Flashcards
2 components of sound
volume: wave amplitude
pitch: wave frequency
3 main regions for hearing
external ear
middle ear
inner ear
structures/function of external ear
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
components of middle ear
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
Structure + function of inner ear
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
difference between middle + external ear and inner ear
air vs fluid filled
labyrinths in ear
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
end of cochlea
helicotrema
3 chambers inside of cochela
3 chambers
- COCHLEAR DUCT
- endolympth
- separates scala vestibuli - SCALA VESTIBULI (top, attached to oval window)
- SCALA TYMPANI (bottom, attached to round window)
- both filled with perilympth
- both connected at helicotrima
perilymph vs endolymph
perilympth: high Na+, low K+
endolympth: low Na+, high K+
structures in cochlear membrane
- 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)
Spiral organ/organ of corti structure + function
Outer hair cells
- 3 rows
- regulate tension on basilar membrane
Inner hair cells
- 1 row
- interpret sound
Supporting cells
tectorial membrane
- gelatanous mass that sits on top of spiral organ
- tops of hair cells embedded in membrane
specialized receptors cells for hearing are known as
hair cells
hair cell structire
- no axon, connected to cochlear nerve
- STERIOCILIA (mircovili on top)
how does sound travel through ear?
- 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
How are loud/quiet and low/high pitch sounds differentiated
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
inner ear depolarization
- 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
structure of microvili on hair cells
- arranged short to tall
- attached to each other by mechanoreceptor springs called TIP LINKS
what happens with no round window?
- Waves from scala tympani have no exit
- bounce back and disrupt signals
neural pathways for hearing
Cochlear nerve
Medulla oblongata
- Cochlear nuclei (can bypass)
- Superior olivary nucleus
Inferior Colliculus (midbrain)
Medial Geniculate nucleus (thalamus)
Primary Auditory Cortex (temporal lobe)
static equilibrium and structures that govern it
head’s position relative to the ground
VESTIBULE
- UTRICLE: horizontal
- SACCULE: vertical
specialized cells within utricle and saccule
MACULA
Static labyrinth (how does static balance work)
- hair cells (MACULA) stimulated by OTOLITHIC MEMBRANE (jelly mass) weighed down by OTOLITHS
- otoliths move in response to gravity
- creates subconscious perception of balance
dynamic labyrinth (how does kinetic balance work
3 semi circular canals (one in each plane)
- AMPULLAE (bulb ends) contain steriocilia that bend in response to movement
- these activate tip links
balance neural pathway
vestibular nerve
vestibular nerve
- cerebellum
- motor nuclei
thalamus
- vestibular area of cortex
