Macula : sensory epithelium inside otolith organs
Vestibular System ● Vestibular macula contains hair cells that lay in a bed of supporting cells with
their cilia projecting upwards, embedded in gelatinous material
Bony and Membranous Labyrinth ● Gelatinous material is weighed down by otoconia (ie. tiny crystals) and together
they form the otolith (ie. ear stone)
In temporal bone filled
● Otoconia helps give weight, and therefore inertia, to the otolith
with perilymph (high Na,
low K)
Bony Labyrinth Benign Paroxysmal Positional Vertigo (BPPV) is caused when otoliths become
Consists of cochlea, displaced, causing vertigo-like symptoms (ie. spinning, nausea) but can be fixed by
vestibule, 3 semicircular shaking the otolith back into place (via epley maneuver)
canals
When you move your head to the left, what happens?
filled with endolymph
(high K, low Na) ● Otoconia will cause some gelatinous material to lag behind, causing the right
hair follicle to be ‘stretched’
Membranous Consists of vestibule ● This causes glycoprotein bridges between the stereocilia to open, allowing K+ to
labyrinth move from endolymph into hair follicle and perilymph
2 parts of membranous ● This movement causes another glutamate increase and AP firing
labyrinth (ie. Utricle and ● Left hair follicle is closed off more and limits the K+ entering and slows AP firing
Saccule) form the otolith
When the head stops moving, what happens?
system
● Main mass of gelatinous material will continue moving with inertia, causing the
● Semicircular ducts (ie. Membranous labyrinth in semicircular canals) becomes stereocilia to be tilted in the other direction
swollen at the ends where they join the utricle (ie. ampulla) ● This causes right hair follicle to close its mechanical receptors to stop any K+
● There are vestibular receptors on the saccule, utricle, and ampulla influx
● It then opens the receptors of left hair follicle and causes them to have K+ and
The otolith system detects head movement glutamate influx, and AP firing
With gravity, what happens to the otolith?
● It sags down in the direction of gravity, pulling on the stereocilia.
● This causes a stretch in glycoproteins and will open up the mechanical receptors
to allow K+ influx into the cell (depolarization) as well as glutamate release and
more AP firing
Hair cells are vertical in the saccule and horizontal in the utricle
● Each hair cell in the macula are oriented differently (not all at same height or
responding to same stimuli) to increase the dynamic range of what's happening
● Every tallest stereocilia faces a different direction so when moved in that
● Hair cells only responds to linear mechanical movement (ie. acceleration) of the direction, it will get activated
head and are sensitive to gravity ● Each direction of movement activates
● Movement can be forward, backwards, up-down, tilting of the head a unique group of hair cells in the
● Stereocilia tilts towards the tallest tip link, which causes K+ channels to open saccule and utricle. They will fire
and enter the hair cell resulting in depolarization messages to the brain via specific
● Depolarization causes more glutamate release and increased afferent firing axons and brain can identify the
● Stereocilia tilting to the shortest tip link will push K+ channels closed to prevent direction of movement depending on
K+ influx and results in hyperpolarization hair cells
, Even when tilting the head, eyes should remain in the center of our eye sockets.
Lateral vestibulospinal tract Medial vestibulospinal tract
Control of eye stability with head movement to the left
Receives info from : Largest part of afferents Semicircular ducts ● Head turns to the left, initially causing fluid to push against the cupula, and
carrying info from the otolith results in AP firing
system ● Afferents terminate at the vestibular nuclei in the brainstem.
They target the : Ipsilateral, anti-gravity Muscles for head movements ○ Vestibular nuclei can activate motor neurons that control extraocular
muscles (eg. soleus, (stability) and reaching muscles
extensors) of the legs to movements (accuracy of ● Left canal input is sent to abducens nuclei on the contralateral side, giving
control posture when there is visually-guided movements) rise to CN VI which innervates the lateral rectus muscle
change in velocity
● Abducens nucleus also sends a rapid impulse to the oculomotor nucleus
contralaterally, especially to the neurons that activate the medial rectus
Semicircular ducts and the Ampulla muscle (of the left eye) = reason for eyes turning right when head turns left
● 3 semicircular canals cover all axes of rotation : anterior, posterior, horizontal ● This response runs through medial longitudinal fasciculus as it is a very
● Semicircular ducts are designed so that hair cells in the ampulla will only large and well-myelinated area (BUT also makes them vulnerable to MS)
respond to rotating head movements (Eg. nodding, shaking) and changes
in velocity Accuracy of vestibulo-ocular reflex
● Ampullary Crest (hill of supporting cells in the ampulla) contains the hair cells ● Flocculonodular lobe of cerebellum interacts with the vestibular system to
● These hair cells project into the endolymph and are embedded in a cupula ensure movements are accurate
(gelatinous membrane) which closes the ducts to the semicircular ducts ● Cerebellum receives input for vestibular nuclei and inner ear afferents
● Stereocilia in the cupula face the same direction and the tallest one is ● Purkinje cells in the cerebellum project down to the vestibular nuclei
towards the utricle. (inhibitory: reduce inhibition if you want to increase power of pathway)
● Turning the head to the left in the left horizontal canal will cause the fluid to ○ Visual input is required for Purkinje fibers to correct movement
lag, which pushes back against the cupula, causing it to bend toward the ● Accessory optic system feeds into the pontine nuclei and olivary nuclei, and
utricle. both feed into the granule cells
● This tilts the hair cells, opens K+ channels and depolarizes afferents ● Accessory optic system can recognize if correction of movement is needed,
● Deceleration of head movement will cause fluid to carry on moving so cupula and they can send impulses to the granule cells, which then cause Purkinje
moves forward, close the channels in the stereocilia to stop AP firing cells to modify the pathway
● Turning the head to the left would hyperpolarize the right horizontal canal
since fluid moves in the same direction but cupula is pushed forward (mirror
image)
● Once head movement becomes constant velocity, endolymph will catch up
with the walls of the canal and stops pressing against the cupula
Vestibular System ● Vestibular macula contains hair cells that lay in a bed of supporting cells with
their cilia projecting upwards, embedded in gelatinous material
Bony and Membranous Labyrinth ● Gelatinous material is weighed down by otoconia (ie. tiny crystals) and together
they form the otolith (ie. ear stone)
In temporal bone filled
● Otoconia helps give weight, and therefore inertia, to the otolith
with perilymph (high Na,
low K)
Bony Labyrinth Benign Paroxysmal Positional Vertigo (BPPV) is caused when otoliths become
Consists of cochlea, displaced, causing vertigo-like symptoms (ie. spinning, nausea) but can be fixed by
vestibule, 3 semicircular shaking the otolith back into place (via epley maneuver)
canals
When you move your head to the left, what happens?
filled with endolymph
(high K, low Na) ● Otoconia will cause some gelatinous material to lag behind, causing the right
hair follicle to be ‘stretched’
Membranous Consists of vestibule ● This causes glycoprotein bridges between the stereocilia to open, allowing K+ to
labyrinth move from endolymph into hair follicle and perilymph
2 parts of membranous ● This movement causes another glutamate increase and AP firing
labyrinth (ie. Utricle and ● Left hair follicle is closed off more and limits the K+ entering and slows AP firing
Saccule) form the otolith
When the head stops moving, what happens?
system
● Main mass of gelatinous material will continue moving with inertia, causing the
● Semicircular ducts (ie. Membranous labyrinth in semicircular canals) becomes stereocilia to be tilted in the other direction
swollen at the ends where they join the utricle (ie. ampulla) ● This causes right hair follicle to close its mechanical receptors to stop any K+
● There are vestibular receptors on the saccule, utricle, and ampulla influx
● It then opens the receptors of left hair follicle and causes them to have K+ and
The otolith system detects head movement glutamate influx, and AP firing
With gravity, what happens to the otolith?
● It sags down in the direction of gravity, pulling on the stereocilia.
● This causes a stretch in glycoproteins and will open up the mechanical receptors
to allow K+ influx into the cell (depolarization) as well as glutamate release and
more AP firing
Hair cells are vertical in the saccule and horizontal in the utricle
● Each hair cell in the macula are oriented differently (not all at same height or
responding to same stimuli) to increase the dynamic range of what's happening
● Every tallest stereocilia faces a different direction so when moved in that
● Hair cells only responds to linear mechanical movement (ie. acceleration) of the direction, it will get activated
head and are sensitive to gravity ● Each direction of movement activates
● Movement can be forward, backwards, up-down, tilting of the head a unique group of hair cells in the
● Stereocilia tilts towards the tallest tip link, which causes K+ channels to open saccule and utricle. They will fire
and enter the hair cell resulting in depolarization messages to the brain via specific
● Depolarization causes more glutamate release and increased afferent firing axons and brain can identify the
● Stereocilia tilting to the shortest tip link will push K+ channels closed to prevent direction of movement depending on
K+ influx and results in hyperpolarization hair cells
, Even when tilting the head, eyes should remain in the center of our eye sockets.
Lateral vestibulospinal tract Medial vestibulospinal tract
Control of eye stability with head movement to the left
Receives info from : Largest part of afferents Semicircular ducts ● Head turns to the left, initially causing fluid to push against the cupula, and
carrying info from the otolith results in AP firing
system ● Afferents terminate at the vestibular nuclei in the brainstem.
They target the : Ipsilateral, anti-gravity Muscles for head movements ○ Vestibular nuclei can activate motor neurons that control extraocular
muscles (eg. soleus, (stability) and reaching muscles
extensors) of the legs to movements (accuracy of ● Left canal input is sent to abducens nuclei on the contralateral side, giving
control posture when there is visually-guided movements) rise to CN VI which innervates the lateral rectus muscle
change in velocity
● Abducens nucleus also sends a rapid impulse to the oculomotor nucleus
contralaterally, especially to the neurons that activate the medial rectus
Semicircular ducts and the Ampulla muscle (of the left eye) = reason for eyes turning right when head turns left
● 3 semicircular canals cover all axes of rotation : anterior, posterior, horizontal ● This response runs through medial longitudinal fasciculus as it is a very
● Semicircular ducts are designed so that hair cells in the ampulla will only large and well-myelinated area (BUT also makes them vulnerable to MS)
respond to rotating head movements (Eg. nodding, shaking) and changes
in velocity Accuracy of vestibulo-ocular reflex
● Ampullary Crest (hill of supporting cells in the ampulla) contains the hair cells ● Flocculonodular lobe of cerebellum interacts with the vestibular system to
● These hair cells project into the endolymph and are embedded in a cupula ensure movements are accurate
(gelatinous membrane) which closes the ducts to the semicircular ducts ● Cerebellum receives input for vestibular nuclei and inner ear afferents
● Stereocilia in the cupula face the same direction and the tallest one is ● Purkinje cells in the cerebellum project down to the vestibular nuclei
towards the utricle. (inhibitory: reduce inhibition if you want to increase power of pathway)
● Turning the head to the left in the left horizontal canal will cause the fluid to ○ Visual input is required for Purkinje fibers to correct movement
lag, which pushes back against the cupula, causing it to bend toward the ● Accessory optic system feeds into the pontine nuclei and olivary nuclei, and
utricle. both feed into the granule cells
● This tilts the hair cells, opens K+ channels and depolarizes afferents ● Accessory optic system can recognize if correction of movement is needed,
● Deceleration of head movement will cause fluid to carry on moving so cupula and they can send impulses to the granule cells, which then cause Purkinje
moves forward, close the channels in the stereocilia to stop AP firing cells to modify the pathway
● Turning the head to the left would hyperpolarize the right horizontal canal
since fluid moves in the same direction but cupula is pushed forward (mirror
image)
● Once head movement becomes constant velocity, endolymph will catch up
with the walls of the canal and stops pressing against the cupula
