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
Signal Vestibular Organs Function
Visual, Proprioceptive, Tactile Inputs
Forebrain: Head Motion: Semicircular Canals Angular accelaration Perceived Orientation
CNS Head Motion: Spinal cord, cerebellum: Linear accelaration Postural Control Saccule and Utricle Head Position: Oculomotor System: Gravity Gaze stabilization utricular macula saccular macula ~3mm
Otolithic membrane
Sensory epithelium
Sense organs within the saccule & utricle are maculae Millions of particles of calcium carbonate (otoconia) add mass to otolithic membrane Linear Movement
Kinocilium
Stereocilia
VIIIth nerve
Resting Excited Inhibited Kinocilium
Utricular Hair Cell Directionality
Anterior Left utricle Right utricle
A B Midline of head Utricular Hair Cell 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 Hearing with your otolith organs, if you are a little fish Each “canal” is a closed tube ~8mm in diameter Ampulla section
Bone Cupula Ampulla Cilia
Hair cell Endolymph Scarpa's Bone ganglion
Crista ampullaris Vestibular nerve
Around 7000 hair cells per crista { All the hair cells are Crista ampullaris 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. sense 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 nystagmus
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 ear 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/ Vertigo/ Falling, Impaired VOR Dizziness/ Circling behavior Disorientation
Motion sickness