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Vestibular System Magnus, 1922

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Vestibular System Magnus, 1922 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 nerve activity 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 .
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