Physiology of Hearing and Balance Flashcards
what dictates the pitch and intensity of sound
frequency dictates pitch
amplitude dictates intensity
what is the frequency of a tuning fork
256 Hz
what are the parameters for hearing on an audiogram
0-20 is healthy 20-40 mild hearing loss 40-70 moderate hearing loss 70-90 severe hearing loss 90+ profound hearing loss
what is the role of the external ear
receive sound
what is microtia and ear canal atresia
when external ear canal is underdeveloped (microtia) or absent (ear canal atresia)
what is the role of the ossicles
amplify the sounds
stapes focuses the energy into small space
increase sound by 30-35 dB
what is the eustachian tube
ventilation for middle ear
resting state is closed
equalises pressure in ear
what opens the eustachian tube
tensor veli palatini and levator palatine muscles
what does dysfunction of the eustachian tube lead to
middle ear negative pressure
what is the role of the oval and round windows
permit transmission of pressure wave in enclosed canal and vibration of the basilar membrane
what is the basilar membrane of the cochlear and how does it work
separates the scala tympani (periphyph) and scala media (endolymph)
vibrations hit this membrane
high frequencies are registered at the start of the membrane, lower frequencies towards the apex
where is the cochlear nerve
runs along the central spine of the cochlear, braches go down into the cochlear canal (spiral ganglions)
how many spirals does the cochlear have
2.5
describe the lay out of the cochlea
Scala media (endolymph) suspended in between scala tympani (perilymph) (bottom one opens to round window) & scala vestibuli (perilymph) (top opens to oval window)
what do the different ionic composition of the scala vestibuli and tympani allow
the powering of the sensory cells
Endo cells high potassium lower sodium, opposite for perilymph- this drives ions into the cells powering them
what is the organ of corti
sensory organ of cochlea
has inner hair cells for sound reception
and outer hair cells for sound modulation
as these move generate APs
what is the pathway of sound APs
pass from 8th cranial nerve through IAC to cochlear nucleus to central pathway (superior olivary complex
to lateral lamniscus then to inferior colliculus)
to primary auditory cortex (superior temporal gyrus)
when can a uterus hear
18 weeks can hear booms and music
26 weeks will respond to sound/voice
how many infants have severe/profound hearing loss at birth
1:1000 (half genetic half acquired)
how many children have severe/profound hearing loss by the age of 10
1:1000 (half genetic half acquired)
how are neonates checked for hearing
The outer hair cells produce sounds
‘OAEs’ can be identified in a normal cochlea – if absent suggest a problem.
where does a cochlear implant insert
into scala tympani
what is normal development of hearing and communication
3 months cooing, recognising mothers voice
6 months babbling, turns to sound or eyes towards sound, makes happy and sad sounds
12 months- makes simple noises, mama/dada, follows instructions, turns to sound
from 12-24 months may hay syllable deletion or simplification, substitutions or using single words to describe a situation
18 months- few words, recognising things
24 months- 2 + word phases, 50+ words, understands questions and follows commands 24 - 36 months ; use three word sentences, aware of rhyme, start with adjectives, understand order, positioning
what are the inputs into the central pathways of the balance system
visual
cardiovascular
vestibular
proprioceptive
what are the outputs of the central pathways of the balance system
vestobulospinal tract
vestibulo-ocular reflex
what does the superior vestibular nerve supply
lateral and anterior SCC
utricle
what does the inferior vesticular nerve supply
posterior SCC
saccule
what are the types of hair cell in the inner ear
kinocilium (biggest) and stereocilia
how does movement of inner ear hairs create action potentials
movement of fluid causes deflection of hairs
if this is towards the kinocilium then depolarisation occurs (increased afferent activity)
if is away from then hyperpolarisation occurs (decreased afferent activity)
how do the SCC detect head movements
work in pairs to detect angular acceleration
inertia of the fluid causes it to lag, and hence generate relative motion in the semicircular duct in the direction opposite that of the head movement
A turn of the head excites the receptors in one ampulla and inhibits receptors in the ampulla on the other side.
what are the otolith organs
the utricle and saccule
what is the function of the otolith organs
maculae of these organs have sterocilia projecting upwards into a gelatinous matrix with otoconia
lend weight and due to gravity brain perceives position and movement when tilting head or linear motions (verticle and horizontal)
how are stercocilia orientated
in all directions so all movements
how are the SCCs orientated
at 90 degrees to each other
where is the cupula
in the ampulla of the SCC
how many ampullas are there in the SCC
one for each SCC
in the vestibulo-ocular reflex which side is excited when you look to the right
the right side is excited (fluid travelling left), the left is inhibited (fluid travelling right)
what is the vestibulo-ocular reflex
controls eye movements to stabilise images during head movements
as head moves in one direction, eyes will move in the opposite
explain how the vestibulo-ocular reflex works
A constant low level of spontaneous activity keeps all the muscles slightly and equally contracted, causing the eyes to look straight ahead. When the head turns, inertia causes the fluid to move more slowly than the head, generating relative fluid motion in the semicircular duct in the opposite direction of the head turn. This moving fluid, shown by arrows in the lumens of the semicircular duct, bends the hair cells on both sides of the head. Because the two sides are mirror images, the stereocilia are bent toward their kinocilium on one side and away from their kinocilium on the other side. Shearing of the stereocilia toward the kinocilium causes a depolarization of the receptor potential and an increase in afferent action potentials. There is an opposite effect on the other side – a decrease in afferent activity. These counteracting bilateral changes in afferent activity affect the vestibular and oculomotor nuclei.
explain VOR nystagmus
vestibular system on one side not working not producing APs
no APs compared ro other side which is producing APs brain will think head is turning
e.g. when you turn your head to the right the APs on right side will increase and left one will decrease
brain tries to correct this by moving eye towards the side of the ear that isn’t working (in this case towards the left). when eye reaches the end on the orbit it will then quicly turn back (fast phase) to the (In this case right side) side that is working
the fast phase is how you name the nystagmus
e.g. this one would be right beating nystagmus
what causes a oscillopsia
when there is no vestibular input
what is the vestibulo spinal tract
motor output to the neck back and leg muscles
what sentral pathway provides motor output to the eyes
Medial longitudinal fasciculus & ocular muscles
in central pathway what connects to the cerebellum
Medial lemniscus & thalamus
