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