Vestibular System - Lois Stevens PDF

Presentation by Lois Stevens Vestibular System Senior Lecturer  Overview Vestibular System – receptors, pathways, descending tracts Vestibular Functions Links to Cerebellum  Vestibular System Sensors: Peripheral organs of VS are found in the v...

Presentation by Lois Stevens Vestibular System Senior Lecturer  Overview Vestibular System – receptors, pathways, descending tracts Vestibular Functions Links to Cerebellum  Vestibular System Sensors: Peripheral organs of VS are found in the vestibule of the inner ear - Labyrinthine apparatus Specifically: Vestibular Hair Cells (ampulla Semi-Circular Canal) Vestibular Hair Cells (maculae Utricle/Saccule)  Semi-Circular Canal Detects angular motion of the head (rotation) 1.Head rotates 2.Force is created by the inertia of the fluid in the semi-circular ducts 3.Displacement of hair cells 4.Action potential of ampullary nerve  Utricle/Saccule Detects tilt of the head Detects acceleration/deceleration  Mechanism-Tilt/Acceleration (Utricle) 1. Head tilts or accelerates 2. Hair cells bend 3. Action potential generated Note: Saccule, another sac like structure of the inner ear, assists utricle in enabling humans to monitor absolute head position in space  Receptors Classify vestibular receptors in terms of: Modality Structure Stimulus  Motor Function VOR – vestibulo-ocular reflex – enables the eyes to move in the opposite direction and at an equal velocity to the head Vestibulo-spinal reflexes – to maintain/regain postural control through activation of vestibulosipinal pathways  Sensory Pathways Sensory receptors Bi-polar cell bodies located in vestibular ganglion (Scarpa’s ganglion) Central processes constitute vestibular (eighth cranial) nerve Synapse in vestibular nuclei  Descending Motor Tracts Lateral vestibular tract–effect on motor neurons innervating limb muscles Medial vestibulospinal tract- terminates in cervical spinal cord-participates in reflex control of neck muscles  Pathways Vest Vest H Nucl Nucl C 8th Cranial N eus eus 2 Way VC V V S S T T L M Skeletal Mm – alpha and gamma systems Vestibular Spinal Reflex  Cerebellar Interaction Don’t forget….. 2 way traffic between cerebellum and Vestibular Nuclei  Pathways Vest Vest H Nucl Nucl C 8th Cranial N eus eus 2 Way VC V V S S T T L M Skeletal Mm – alpha and gamma systems  Summary of Function Produce complex patterns of facilitation and inhibition in motor neurons innervating widely distributed muscles = postural control (balance) Purpose is to restore/maintain stability so that spinal reflexes and volitional movement can have the desired effect Helps to modulate tone Vestibulo-ocular Reflex-stabilises visual images on retina during movement Maintains our position in relation to gravity Vestibulo-spinal Reflex