UNIT 7: Inner Ear Flashcards
the inner ear is comprised of
the organs of hearing and equilibrium
structurally linked
organs of hearing and equilibrium are innervated by
vestibulocochlear nerv CN VIII
systems of hearing and equilibrium consist of
osseous labyrinth and membranous labyrinth
osseous labyrinth includes
semicircular canals, vestibule, cochlea
membranous labyrinth consists of
semicircular ducts, utricle, saccule, cochlear duct
the human balance sys is comprised of
vestibular sys
vision
proprioception
CN VIII - vestibulocochlear has 2 components
vestibular and auditory
describe the osseous labyrinth… fluid?… how many parts?
series of continuous spaces surrounded by bone
spaces are fluid filled - fluid is perilymph
has 3 parts
3 parts of osseous labyrinth
semicircular canals (vestibular sys)
vestibule (vestibular sys)
cochlea (auditory sys)
semicircular canals are 3 canals that for the …. names of the canals are…. each SCC is approx …
posterior portion of the osseous labyrinth
anterior, posterior, and lateral
2/3 of a complete circle
each SCC has a dilated portion called an _____, SCCs enclose the ________ of the _______ labyrinth
ampulla
semicircular ducts
membranous labyrinth
Vestibule is the
middle dilated portion of the osseous labyrinth
______ and _____ of the middle ear are located on the vestibule
fenestra vestibuli
fenestra cochleae
vestibular aqueduct passes…
passes posterioinferiorly from the vestibule and opens on the posterior surface of the pertous bone
transmits endoymphatic duct and sac
what does the vestibule house
the utricle and saccule of the membranous labyrinth
cochlea is a ____ tube w approx ____ turns, its wide basal turn forms the _____
helical
2 3/4 turns
promontory
the cochlea lies on its side in the ____, with its apex pointing _____
petrous bone
anterolaterally
the cochlea encloses the
cochlear duct of the membranous labyrinth
cochlea has a bony core called the _____, what passes thru this structure?
modiolus
cochlear portion of CN VIII and spiral ganglia pass thru it
shelves of bone project laterally from the modiolus called the
osseous spiral laminae
spiral laminae partially divide the cavity of the cochlea into 2 portions…
scala vestibuli anteriorly and scala tympani posteriorly
at the apex of the cochlea, scala vestibulu and scala tympani communicate via a small opening called
helicotrema
division of the cochlea is completed by the
cochlear duct (scala media) of the membranous labyrinth
scala vestibuli begins at
fenestra vestibuli (oval window), which is occupied by the footplate of the stapes
scala tympani ends at
the fenestra cochleae (round window), which is closed by a secondary tympanic membrane
both scala vestibuli and tympani are filled w
perilymph
aka osseous labyrinth
perilymph is
an extracellular fluid, similar in composition to plasma or cerebrospinal fluid
the membranous labyrinth is…
a series of connected ducts and sacs housed w/i and protected by the osseous labyrinth
membranous labyrinth is comprised of
semicircular ducts
utricle
saccule
cochlear duct/scala media
ducts and sacs in the membranous labyrinth are filled w
endolymph
describe endolymph
more viscous than perilymph, similar composition to intracellular fluid
endolymph is produced by
stria vascularis in the cochlear duct
moved toward the venous sys at the base of the brain by the endolymphatic duct
semicircular ducts are approx ___ of the diameter of the SC canals
1/4
each SCD has an _____ end, which contains …
ampullated end
contains a patch of sensory epithelium - the ampullary crest or crista ampullaris
crista ampullaris is
w/i the SCDs
a patch of sensory epithelium
sensory receptors for detecting rotational movement of the head
contains hair cells
the hair cells of crista ampullaris have basal parts which synpase w
the vestibular nerve of CN VIII
crista ampullaris hair cells have stereocilia which project into a
tall, jelly-like mass called the cupula
@crista ampullaris: as the head rotates, endolymph moves opposite to the direction of rotation and…
pushes on the cupula bending the stereocillia
utricle communicates w
semicircular ducts
saccule communicates w the…. via the…
cochlear duct
via the utriculosaccular duct
both the utricle and saccule contain..
a patch of sensory epithelium called the macula
utricle and saccule monitor the position of the…. and straight-line changes in …
head, aka static equilibirum (lying down, sitting up etc)
in speed and direction of head movements, aka linear acceleration (ex. walking, going up an elevator)
maculae is a
patch of epithelium w columnar supporting cells and scattered hair cells
hair cells in the maculae synapse w
fibres of the vestibular nerve of CN VIII
maculae: each hair cells has …. and the tips of the stereocilia are …
many stereocilia protruding from its apex
tips are embedded in overlying otolithic membrane
otolithic membrane of the maculae is…
a jelly like disc containing heavy crystals of calcium carbonate called otoliths
macula of the utricle is for ___ orientation, which indicates…
horizontal
indicates head tilting and linear movement - forward, backward, sideways movement in a straight line
macula of the saccule is for ___ orientation, which indicates…
vertical orientation
indicates head’s upright position and linear movement - forward, backward, upward, downward movement
how is the otolithic membrane like a sac of marbles
So it will go in the opposite direction only when you are walking forward, back … think of dragging a sac of marbles behind you, hair cells will be bent behind you in opp direction
But if you are tilting head down gravity will pull sac of marbles down, and the hair cells will bend down in the same direction
describe the cochlear duct/scala media
spiral tube housed in cochlea (25-35 mm)
occupies the lateral portion - completes the division of the cochlea, started by the spiral laminae, into scala vestibuli and scala tympani
what 3 things form the “triangle” of the cochlear duct
basilar membrane
vestibular membrane
spiral ligament
basilar membrane is
floor of cochlear duct/scala media
supprots the organ of hearing = organ of corti
vestibular membrane is
roof of the cochlear duct
joins the basilar mem at the helicotrema
spiral ligament is
forms the lateral wall of the cochlear duct
stria vascularis on surface of spiral ligament
organ of corti is…
a cellular structure along the length of the cochlear duct
many cells serve a supportive function
hair cells of the organ of corti have stereocillia that project from….which are embedded in….
apex of hair cells
the overhanging jelly-like tectorial membrane
hair cells of the organ of corti are innervated by
cochlear nerve of CN VII
movement of the fluid in the cochlear duct leads to
movement of the basilar membrane, bending the stereocillia and generating a nerve impulse
how many rows of inner hair cells on the organ of corti?
1
approx _____ IHCs on the medial side of the tunnel of corti
3500
how many stereocilia on each IHC? how are they arranged?
40 - arranged in parallel rows, dec in height towards the modiolus
how many rows of outer hair cells on organ of corti?
3 to 5
how many outer hair cells?
1200
how many stereocilia on OHCs? how are they arranged?
150 stereocilia per OHC
arranged in the form of a V or W (base of letter points toward spiral lig) w dec height toward the modiolus
describe size/shape of OHCs
long and thin (cylindrical)
tallest tips of OHC stereocilia are embedded in the tectorial membrane
describe size/shape IHCs
fat and round
tips of IHC stereocilia are not embedded in the tectorial membrane
if the IHCs are not embedded in the tectorial membrane how do they move?
Outer hair cells are tall and thin, embedded in tectorial membrane, when the basilar membrane moves, the outer hair cells embedded move the tectorial membrane and this creates turbulence in the endolymp which makes the inner hair cells move
We need the outer hair cells to help the inner hair cells fire
afferent fibres send sound information in the cochlea to the …… and have cells bodies in the ….
CNS
spiral ganglion
______ make up 95% of the nerve fibres in the cochlear nerve
Type I myelinated
many type I fibres innervate a single IHC
____ make up 5% of nerve fibres in the cochlear nerve
type II unmyelinated
one type II fibre innervates many OHCs
what are the 3 functions of the cochlea
transforms sound vibrations into neural impulses
separates sounds according to their freq
compresses amplitude of sounds
IHCs have most responsibility of….
hearing, that is sending afferent info regarding sound to CNS (function #1)
IHCs selectively respond to…
frequency (function #2)
OHCs are thought of as ….
amplifiers - they have the ability to change cell shape by receiving efferent fibres from the descending auditory nervous sys (function #3)
OHCs compensate for loss of energy w/i the ….
cochlea, improving the ear’s sensitivity and sharpening ist freq selectivity for weak sounds
OHCs inc the movement of …
the basilar membrane to amplify the activity of the IHCs
structure of the basilar membrane influences
its resonant properties and freq response characteristics - like a diving board
narrow and stiff at base and wide and floppy at apex
low freq sound cause vibration at the apex of the cochlea
what are the steps of hearing
Sound waves enter the ear through EAM
TM vibrates from sound waves, sending vibrations to ossicles
Ossicles amplify the sound vibrations and send them through the oval window to the cochlea of the inner ear
The vibrations cause the fluid inside the cochlea to ripple, a travelling wave forms along the basilar membrane – the hair cells sitting on top of the basilar membrane ride the way
As the hair cells move up and down the stereocilia on top of the hair cells bump against the tectorial membrane, causing them to bend
When the stereocilia bend it opens channels that are at the tips of the stereocilia, chemicals rush into the cells creating an electrical signal
Auditory nerve carries electrical signal to the brain
meniere’s disease
too much endolymph
leads to both hearing and vestibular disturbance (tinnnitis, fluctuating HL, rotatory vertigo)
hearing returns to normal after attacks early in the disease process, as the disease progresses, residual hearing loss accumulates, and hearing loss spreads from low freq to high freq
benign paroxysmal positional vertigo (BPPV)
otolithic memebrane falls off utricle due to injury, age, drug effects - migrates toward semicircular ducts
come to rest in a SCD (usually posterior) and creates a sensation of vertigo
symptoms worsen if they rest on the cupula
debilitating; always precipitated by a change in head position like rolling over in bed
