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The Vestibular System
Magnus, 1922
The Vestibular System Senses:
• Angular Acceleration (in 3D)
• Linear Acceleration (in 3D)
Which way is up? Where am I going?
Inertial Guidance System
Head Motion:Angular accelaration
Head Motion:Linear accelaration
Head Position:Gravity
Semicircular Canals
Saccule and Utricle
CNS
Visual,Proprioceptive,Tactile Inputs
Forebrain:Perceived Orientation
Spinal cord, cerebellum:Postural Control
Oculomotor System:Gaze stabilization
SignalVestibular
Organs Function
utricular macula saccular macula
Otolithic membrane
Sensory epithelium
Sense organs within the saccule & utricle are maculae
Millions of particles of calcium carbonate (otoconia)
add mass to otolithic membrane
~3mm
Linear Movement
Stereocilia
Kinocilium
VIIIth nerve
Resting Excited Inhibited
Kinocilium
Anterior
Midline of head
Left utricle Right utricle
A B
Utricular Hair Cell Directionality
Anterior
Midline of head
Left utricle Right utricle
A B
Utricular Hair Cell Directionality
Excited Inhibited
Head and body tilted to right
Anterior
Midline of head
Left utricle Right utricle
A B
Utricular Hair Cell Directionality
Head and body tilted to left
ExcitedInhibited
Hearing with your otolith organs, if you are a little fish
Each “canal” is a closed tube ~8mm in diameter
Ampulla
Crista ampullaris Vestibular nerve
EndolymphHair cell
Cupula
Cilia
Scarpa's
ganglion
Bone
Bone
Ampulla section
Around 7000 hair cells per crista
{
Crista ampullarisAll the hair cells are
polarized in the same
direction.
Linear
Acceleration
Start
Rotation
Continue
Rotation
Stop
Rotation
A B C Dfluid
tube rotation relative fluid flow
Canal physics
Ampulla
Crista ampullaris Vestibular nerve
EndolymphHair cell
Cupula
Cilia
Scarpa's
ganglion
Bone
Bone
Utriculo-
petal flowUtriculo-
fugal flow
Ampulla
Head rotation to right
40
20
0
0
20
40
0 10 20 30 40 50 60
Time (sec)
Ve
stibu
lar
ne
rve
activity
(im
pu
lse
s p
er
se
co
nd
)
Right lateral canal
Left lateral canal
Canal
AmpullaUtricle
Canal output
Utriculopetal
Flow
Utriculofugal
Flow
Semicircular canals are paired / complementary
Geometry of Semicircular Canals
A. Posture and locomotion B. Gaze Stabilization C. Position sense
Reticular
Formation
Reticulospinal tr. Vestibulospinal tr.
Vestibular nuclei
Scarpa's ganglion
Cerebellum
III
IV
VI
MLF
To thalamus and cortex
Central Connections
A. Posture and locomotion B. Gaze Stabilization C. Position sense
Reticular
Formation
Reticulospinal tr. Vestibulospinal tr.
Vestibular nuclei
Scarpa's ganglion
Cerebellum
III
IV
VI
MLF
To thalamus and cortex
A. Posture and locomotion B. Gaze Stabilization C. Position sense
Reticular
Formation
Reticulospinal tr. Vestibulospinal tr.
Vestibular nuclei
Scarpa's ganglion
Cerebellum
III
IV
VI
MLF
To thalamus and cortex
Posture and locomotion Position sense Gaze stabilization
Gaze direction
Canals
View straight ahead Turn head to right
Vestibulo-ocular reflex
VOR
Vestibular nystagmus
Head to
Right
Eye P
ositio
n
Time
Slow Phase Quick PhaseLeft
Right
Sawtooth pattern movement of the eyes made up of
a slow (VOR) phase and fast (saccadic reset) phase
Lateral canal
30o
LA
P
Caloric Test
Test of intact vestibular function using thermal
irrigation of the ear
Late
ral c
anal
30
o
L
A
P
Warm water
Tympanic
membrane
Middle
ear
External
auditory meatus
Utricle
Region of warm,
less dense
endolymph rises
Utriculopetal flow
As if rotation to right
Slow phase left
Quick phase right
Right Ear
[COWS: Cold Opposite Warm Same]
Disorders of the Vestibular System
A. Posture & Locomotion B. Gaze Stabilization C. Position Sense
Disequilibrium/
Falling,
Circling behavior
Impaired VOR
Vertigo/
Dizziness/
Disorientation
Motion sickness
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