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Sensorimotor Control of Behavior: Somatosensation Lecture 8.

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Presentation on theme: "Sensorimotor Control of Behavior: Somatosensation Lecture 8."— Presentation transcript:

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 ~


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