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Sensorimotor Control of Behavior: Somatosensation

Sensorimotor Control of Behavior: Somatosensation. Lecture 8. Somatosensation. Sensory info from body Cutaneous senses exteroceptors touch / pain Kinesthesia interoceptors body position & movement ~. Somatosensory cortex. S1 - Postcentral Gyrus Somatotopic Organization

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Sensorimotor Control of Behavior: Somatosensation

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  1. Sensorimotor Control of Behavior: Somatosensation Lecture 8

  2. Somatosensation • Sensory info from body • Cutaneous senses • exteroceptors • touch / pain • Kinesthesia • interoceptors • body position & movement ~

  3. Somatosensory cortex • S1 - Postcentral Gyrus • Somatotopic Organization • topographic representation of body • Distorted Homunculus • disproportionate amount of cortex for body parts • high sensitivity: large cortical area ~

  4. Somatosensory Cortex • Formation of a Body Image • Does not simply respond to sensory input • Phantom Limbs • after amputation • also pain ~

  5. M1 PPC S1

  6. Kinesthesia

  7. Kinesthesia • Body Position & Movement • proprioception • Joint information • Pacinian corpuscles & Ruffini endings • Muscle & tendon information • changes in tension • Golgi tendon organ • muscle spindle fibers ~

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

  9. 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 ~

  10. 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 ~

  11. Muscle-Spindle Receptors • Muscle length detectors • Parallel with extrafusal fibers • Low threshold • Monosynaptic stretch reflex • Postural adjustments • Muscle tonus • Sensory neuron ---> alpha motor neurons monosynaptic excitation disynaptic inhibition ~

  12. Dorsal M S + + - + Ventral +

  13. Golgi Tendon Organ • Gauges muscle tension • high threshold • Stretch receptor • safety mechanism • controlled muscle contraction ~

  14. Dorsal GTO + - Ventral Inhibits alpha motor neuron +

  15. 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 ~

  16. The Orienting Senses

  17. 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 ~

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

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

  20. Acceleration to right Acceleration to right tilted At rest Direction of gravity

  21. 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 ~

  22. Ampulla Crista hair cells Cupula Semicircular canals Utricle

  23. 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) ~

  24. 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 ~

  25. Sensorimotor Integration

  26. Sensorimotor Integration • Somatosensory cortex • provides spatial coordinates • Motor Cortex • executes movements • Results in meaningful behavior ~

  27. Posterior Parietal Cortex - PPC • Constructs spatial coordinates for behavior • Apraxia • inability to purposefully organize movements • Left parietal apraxia • bilateral inability to perform requested movements ~

  28. Constructional apraxia - damage to PPC

  29. Spatial Neglect • Contralateral neglect • neglect of left side of body and world • Damage to right PPC • map of body & space destroyed ~

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