Physiology of Hearing and Balance Flashcards
what dictates the pitch and intensity of sound?
frequency of wave = pitch
amplitude of wave = intensity
what frequency of sound can human perceive?
20Hz - 20,000Hz
what is the normal reference for normal hearing?
should be below 20 (0 is the healthy hearing ability of a 20 y/o male for reference)
20-40 = mild hearing loss
40-60 = moderate etc
what is impedence matching?
the transfer of vibration/waves from air to liquid
occurs at the oval window where vibration of the stapes causes pressure waves in the endolymph in the cochlear duct
what does the ossicular chain do?
acts as a piston or lever arm with varying efficiency depending on frequency of sound transmitted
what is the ratio of malleus handle to incus long process and what is the significance of this?
1.3:1
mechanical gain of decibels
what is the eustachian tube?
ventilation pathway for middle ear mucosa
joins middle ear to nasopharynx
what does the eustachian tube do?
equalises pressure in the middle ear to the outside pressure
closed at rest
opened by tensor veli palatine and levator palatine muscles in order to change pressure
what are the 2 openings in the cochlea and what are their functions?
oval and round windows
allow transmission of pressure wave in enclosed canal and vibration of the basilar membrane
hair cells in the cochlea are of varying length, what is the implication of this?
particular wavelength/frequency of sound hits a particular area/length of hair cells in cochlea
signals from this area travel to the brain and the brain can therefore determine pitch of sound
if this part damaged - cant hear that pitch
where are short/long hair cells found in the cochlea and what frequency of sound stimulates each?
short hair cells at base of cochlea = stimulated by high frequency sound
long hair cells at tip of cochlea spiral = stimulated by low frequency sound
how are hair cells used in universal neonatal screening?
outer hair cells
produce otoacoustic emission (OAE - basically a little sound) which can be identified in a normal cochlea in response to sound
can suggest a problem if absent
used for screening
normal speech ability at 3 months?
cooing
recognizes mother’s voice
normal speech development at 6 months?
babbling
turns to sound or eyes towards sound
normal speech and hearing development at 12 months?
may make simple noises
mama/dada
follows intructions
turns to sound
normal speech difficulties at 12-24 months?
syllable deletion (retain stressed syllable e.g not say the “ba” in “banana”)
syllable simplification (leave out the S in stop)
substitutions (replace R with L or W)
may use single words to describe a situation
speech at 18 months?
may say a few words
recognise body parts, animals, simple commands
speech at 24 months?
2 word phrases
50+ words
understands questions and follows commands
speech at 24-36 months?
3 word sentences aware of rhyme start with adjectives understand order positioning
how many turns in cochlea?
2.5
describe the structure of the cochlear canal
tube divided into parts upper portion = scala vestibuli (perilymph) bottom portion = scala tympani scala media (cochlear duct) sits between the layers - suspended by spiral ligament
what is contained within the cochlear duct?
basillar membrane
organ of corti
endolymph
what drives the production of current in the cochlea?
difference in ion concentrations between scala media (endolymph) and scala vestibuli (perilymph)
stimulation opens channels for the movement of potassium
what is the function of inner vs outer hair cells in the cochlea?
inner = sound perception outer = sound amplification (have motor ability so beat to increase vibration of basilar membrane)
describe the pathway through which APs from the cochlear nerve
E COLI
- eighth cranial nerve (vestibulocochlear)
- cochlear nucleus
- olivary complex
- lateral lemniscus
- inferior colliculus
what does the middle ear do?
mechanical force amplifier
amplifies the force of vibration (which is travelling through air) so it can travel through liquid in the cochlea
which 4 systems have an input in contributing to balance?
visual
proprioceptive
cardiovascular
vestibular
what are the 2 outputs in the balance systems?
vestibulospinal tract
vestibulo-ocular reflex
what is the modified rombergs test?
test of balance which tests vestibular input and vestibulospinal output
stand on firm floor with eyes closed and attempt to stay balanced while doctor nudges
repeat while standing on deep foam box
should be able to stay upright (more difficult on foam box)
what nerve innervates the lateral/anterior Semi-circular canal and utricle?
superior vestibulocochlear nerve
what does the inferior vestibulocochlear nerve innervate?
posterior semi-circular canal and saccule
describe the features of the hair cells of the inner ear
consist of several tiny cilia
tallest projection at the apex = kinocilium
smaller projections surrounding = stereocilia
resting potential = 90 spikes per second
how do the hair cells of the inner ear affect membrane potential?
movement of endolymph moves the hair cells
movement towards the kinocilium = depolarisation
movement away from the kinocilium = hyperpolarisation
what are the otolith organs?
utricle and saccule of the vestibule
what do the otolith organs do?
maculae of these organs have stereocilia projecting upwards into a gelatinous matrix with otoconia (calcium carbonate crystals)
lend weight due to gravity - brain perceives the position and movement of these when tilting the head or moving in linear motion
what impact does the orientation of the otolith organs have?
otolith organs are at right angles to each other so movement in different planes will affect each on differently
stereocilia orientated in all directions so all movements are perceived by changes in resting potential/firing rate
what effect does the orientation of the semi-circular canals have?
orientated at 90 degrees to each other so paired, equal and opposite
canals are paired to that when you turn your head one way, this has an affect on one canal and the opposite affect on the opposite canal
what is the cupula?
cluster of hair cells embedded in a jelly-like mould which sits in the ampulla of a semi-circular canal
movement of perilymph causes deflection of the cupula which causes stereocilia to deflect
what happens at each side of the semi-circular canal on head movement to the right?
right side = excitation
left side = inhibition
what does the vestibulo-ocular reflex allow?
allows movement of eyes in opposite direction of head movement to allow eyes to remain focused on a fixed point while head is moving
activation of the vestibular system causes eye movement
how is the vestibulo-ocular reflex involved in dizziness?
brain perceives difference in direction of movement of head and eyes as a mismatch and perceives this as the body spinning
what happens in a loss of vestibulo-ocular reflex?
nystagmus
brain doesn’t think head is moving however the stimulus is still there so they eyes do a quick flick to the side and then back to centre
what is oscillopsia?
visual disturbance in which objects in the visual field appear to oscillate
due to complete lack of vestibular input
there are outputs to what 3 systems in maintaining balance?
vestibulospinal tract - motor output to neck, back, leg muscles
medial longitudinal fasciculus and ocular muscles - motor output to eyes
medial lemniscus and thalamus to cerebrum
