The Vestibular System Lesson 18 Orientation The Vestibular

The Vestibular System Lesson 18

Orientation: The Vestibular System n Position & motion of body in space l critical for adaptive interaction l largely unnoticed l except unusual conditions motion sickness: nausea, dizziness n Maintenance of balance & posture l coordinating body position with other sensory information ~

Receptors for Orientation Inner ear n Gravity detectors l plane of reference n Mechanoreceptors n Vestibular Organs l otocysts n • saccule • utricle l semicircular canals ~

Otocysts n Liquid-filled “ear sacs” l lined with hair cells l contain otoliths “ear stones : direction of acceleration saccule: vertical movement n utricle: horizontal movement ~ n

At rest tilted Direction of gravity Acceleration to right

Semicircular Canals n Rotary acceleration l direction & extent of circular movement any direction 3 fluid-filled canals l right angles to each other l 1 for each major plane n Movement causes fluid to circulate l displaces cupula ~ n

Semicircular canals Ampulla Crista hair cells Utricle Cupula

Vestibular Pathway Vestibulocochlear nerve (VIII) l Some axons directly to cerebellum n Most axons to medulla n vestibular nuclei l l cerebellum, spinal cord, medulla & pons motor nuclei for eyes (III, IV, & VI) compensates for movement of head l temporal cortex (dizziness) ~

Vestibular Stimulation Perceive movement in an airplane? l No, persisting passive movement l Otoliths, fluid move at same speed n Vestibular system detects active movements l changes in rate of motion n acceleration n heating/cooling fluid perception of body motion ~

Visual Illusions of Movement n Self vection l perceive you are moving, but not l 2 adjacent trains, cars l restricted visual field no background information ~

Visual Illusions of Movement n Postural sway l visual cues help maintain posture l illuminated booth, that can sway l individual sways with surroundings l no vestibular stimulation ~

Motion Sickness n During passive transportation e. g. riding in car, but not when driving l unusual circumstances e. g amusement park rides usually not steady motion n Symptoms: nausea, dizziness, vertigo, cold sweats, hyperventilation ~ l

Cause of Motion Sickness Sensory conflict theory l Mismatch b/n visual & vestibular info n Treisman (1977): cause of vomiting l ingestion of natural toxins disrupt visual input & motor coordination l vomiting adaptive response to inappropriate stimulus: toxins/motion n Dogs: remove vestibular system l toxins no vomiting ~ n