1. Sensorimotor Control of Behavior: Somatosensation Lecture 8

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

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

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

5. M1 S1 PPC

6. Kinesthesia

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

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

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

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

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

12. Dorsal Ventral + + MSMS - + +

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

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

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

16. The Orienting Senses

17. 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 ~

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

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

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

21. Semicircular Canals n Rotary acceleration l direction & extent of circular movement any direction n 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 ~

22. Semicircular canals Utricle Ampulla Crista hair cells Cupula

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

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

25. Sensorimotor Integration

26. n Somatosensory cortex l provides spatial coordinates n Motor Cortex l executes movements n Results in meaningful behavior ~

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

28. n Constructional apraxia - damage to PPC

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