Kinesthesis the Vestibular System

1. Kinesthesis &the Vestibular System Lecture 16

2. Kinesthesis Body Position & Movement proprioception Skin stretch cutaneous mechanoreceptors Joint information encapsulated mechanoreceptors Muscle & tendon information stretch receptors ~

3. Cutaneous Receptors Stretching of the skin Limited role in proprioception Ruffini Endings slow adapting population of neurons responding simultaneously ~

4. Cutaneous Receptors Role depends on location Anesthetize skin assess ability to detect passive movement Knee: no affect on proprioception Mouth, hands, & feet proprioception significantly reduced ~

5. Joint Receptors Within joint capsule Primary perception is pain Pressure-sensitive mechanoreceptors Ruffini endings Paciniform corpuscles small, elongated Pacinian corpuscles ~

6. Joint Receptors Also limited role in detecting limb position Anesthetize/remove joint capsule no loss of proprioception Protective role Afferent fibers respond only at extreme positions Signals hyperextension or hyperflexion ~

7. Muscle Receptors Major role in proprioception Stretch receptors detect changes in tension 2 types of receptors Muscle spindles & Golgi tendon organs differences in threshold & location ~

8. Muscle Spindles (MS) Length detectors Complex encapsulated ending in parallel with extrafusal muscle fibers provide force for movement Detect dynamic and static stretch 2 types of sensory afferents Involved in knee-jerk reflex ~

9. MS: Anatomy & Function Intrafusal muscle fibers weak, not involved in movement sensitivity controlled by g motor neurons Sensory neurons tightly wrapped around intrafusal fibers ~

10. MS: Anatomy & Function Type I: large diameter sensitive to early, rapid change in length firing rate varies with velocity & length Type II: smaller, slower more sensitive to sustained stretch ~

11. Golgi Tendon Organs (GTO) Tension detrectors Encapsulated organ in tendons in-line with 10-20 muscle fibers Type 1 afferents ... terminate among collagen fibers Stretch compresses ends of afferents increases firing rate ~

12. GTO: Function Inhibits muscle contraction Control of motor acts slow contraction as force increases e.g., holding an egg breaks if too much force Autogenic inhibition safety mechanism too much tension ---> damage ~

13. Haptic Perception Perception of geometric properties skin + kinesthesic information shape, texture, dimensions Active touch self-produced exploration Tactual stereognosis input from both hands unitary experience ~

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

15. Receptors for Orientation Inner ear Gravity detectors plane of reference Mechanoreceptors Vestibular Organs otocysts saccule utricle semicircular canals ~

16. Otocysts Liquid-filled �ear sacs� lined with hair cells contain otoliths �ear stones : direction of acceleration saccule: vertical movement utricle: horizontal movement ~

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

19. Semicircular canals

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

21. Input to Vestibular System Other sensory information eyes trunk & neck limbs cerebellum Constant postural adjustments Maintains visual image fixed on retina maintains center of gravity during movement ~

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

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

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

25. Vestibular Disorders Meniere�s Disease Symptoms Vertigo, tinnitus, hearing loss Excess endolymph ---> � pressure Exact cause unknown ~

26. Vestibular Disorders Vestibular neuronitis caused by virus or tiny blood clot 4-5 red blood cells sufficient sudden loss of function in 1 ear person becomes violently dizzy may not be able to walk at all lasts days to weeks ~