The Magnus, 1922

The Vestibular System :

• Angular Acceleration (in 3D)

• Linear Acceleration (in 3D)

Which way is up? Where am I going? Inertial Guidance System

Signal Vestibular Organs Function

Visual, Proprioceptive, Tactile Inputs

Forebrain: Head Motion: Angular accelaration Perceived Orientation

CNS Head Motion: Spinal cord, cerebellum: Linear accelaration Postural Control and Head Position: Oculomotor System: Gravity Gaze stabilization utricular macula saccular macula ~3mm

Otolithic membrane

Sensory

Sense organs within the saccule & utricle are maculae Millions of particles of calcium carbonate (otoconia) add mass to Linear Movement

Kinocilium

Stereocilia

VIIIth nerve

Resting Excited Inhibited

Utricular Hair Directionality

Anterior Left utricle Right utricle

A B Midline of head Utricular Directionality

Anterior Left utricle Right utricle

A B Excited Inhibited Midline of head

Head and body tilted to right Utricular Hair Cell Directionality

Anterior Left utricle Right utricle

A B Inhibited Excited Midline of head

Head and body tilted to left with your organs, if you are a little fish Each “canal” is a closed tube ~8mm in diameter Ampulla section

Bone Cupula Ampulla Cilia

Hair cell Scarpa's Bone ganglion

Crista ampullaris

Around 7000 hair cells per crista { All the hair cells are polarized in the same direction. Canal physics

A fluid B C D

Linear Start Continue Stop Acceleration Rotation Rotation Rotation

tube rotation relative fluid flow Bone Cupula Ampulla Cilia

Hair cell Endolymph Scarpa's Bone ganglion

Crista ampullaris Vestibular nerve Utriculo- Utriculo- petal flow fugal flow

Ampulla Canal output

Ampulla Utriculopetal Utricle Flow Right lateral canal 40 Canal

20

0 Utriculofugal

40 Flow Left lateral canal

20

Vestibular nerveactivity Vestibular per(impulses second) 0 Head rotation to right

0 10 20 30 40 50 60

Time (sec) Semicircular canals are paired / complementary Geometry of Semicircular Canals Central Connections

To thalamus and cortex To thalamus and cortex To thalamus and cortex III III III IV IV IV

Cerebellum Cerebellum Cerebellum VI VI Scarpa's ganglion Scarpa's ganglion VI Scarpa's ganglion Reticular ReticularMLF MLF Vestibular nuclei Vestibular nuclei Reticular Formation MLF Formation Formation Vestibular nuclei Reticulospinal tr. Vestibulospinal tr. Reticulospinal tr. Vestibulospinal tr. Reticulospinal tr. Vestibulospinal tr.

A. Posture and locomotion B. A.Gaze Posture Stabilization and locomotion C. PositionB. Gaze Stabilization C. Position sense A. Posture andPosture locomotion and locomotionB. Gaze Stabilization PositionC. Position sense sense Gaze stabilization Vestibulo-ocular reflex VOR

Gaze direction

Canals

View straight ahead Turn head to right Vestibular

Sawtooth pattern movement of the eyes made up of a slow (VOR) phase and fast (saccadic reset) phase

Head to Right

Left Slow Phase Quick Phase Eye Position Eye Right Time Caloric Test Test of intact vestibular function using thermal irrigation of the o

30

Lateral canal Lateral canal

30o

A L

P

L

A

P Tympanic Utriculopetal flow membrane

Middle Utricle Right Ear ear As if rotation to right

Warm water Slow phase left Region of warm, External less dense auditory meatus endolymph rises Quick phase right

[COWS: Cold Opposite Warm Same] Disorders of the Vestibular System

A. Posture & Locomotion B. Gaze Stabilization C. Position Sense

Disequilibrium/ / Falling, Impaired VOR Dizziness/ Circling behavior Disorientation

Motion sickness