Hearing Physiology + Equilibrium

What are sound waves and what does it cause eardrums to do

soundwaves = vibrations in the ear → causes eardrums (tympanic membrane) to vibrate

What does eardrum vibration cause

auditory ossicle movements in the middle ear

also starts vibrating → amplifies pressure

Malleus → incus → stapes

What does ossicle movement do

stapes pushes oval window → presses fluid of inner ear (cochlear specifically) → pressure waves form starting in the scala vestibuli

What does fluid movement vibrate

basilar membrane of cochlea

What happens after fluid movement and waves in the inner ear

hair cells are excited → stimulating local neurons of CN VIII → signal to brain

Auditory pathway from hair cell

Hair cells → cochlear nerve → cochlear nuclei → medulla → midbrain → thalamus → primary auditory cortex( temporal lobe)

Auditory pathway from sound

Sound waves → vibrations → mechanical vibrations in middle ear → fluid movement and waves in inner ear → nerve signal of CN VIII

Ptich

different hair cells detect different impulses as pitch

Loudness is detected

increased number of action potentials when the hair
cells experience larger deflections

measured by decibels

Localization of sound and what does it depend on

how you know where sound comes from

depends on intensity and timing of sound waves reaching both ears

What is equilibrium /balance and orienation done by

vestibular apparatus

What does the vestibular apparatus contain

equilibrium receptors and semi circular canals

What are the two equilibrium receptors and what do they detect

where are they

utricle and saccule receptors

detect gravity and linear acceleration (drviing car)

in vestibule

Semi circular canal

dynamic equilibrium → angular movements (spinning)

Endolymph

fluid in semicircular canals → when rotating endolymph lags behind because of inertia bending cupula and hair cells → detects rotation

Equilibrium pathway

vestibular receptor → vestibular nuclei (brainstem) → cerebellum

Balance depends on what 3 inputs

vestibular receptor, visual receptor, somatic receptor → if one disagrees → dizziness

Sensory mismatch

sensory systems disagree