Motor system5 posture

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Motor system5 posture

  1. 1. Physiology of Posture Prof. Vajira Weerasinghe Dept of Physiology
  2. 3. Dynamic vs static nature of motor control <ul><li>Static stability </li></ul><ul><ul><li>is dependent on the position of the centre of gravity with respect to the base of support </li></ul></ul><ul><li>whereas dynamic stability </li></ul><ul><ul><li>is dependent more on the moment of inertia of the body </li></ul></ul>
  3. 4. Adult vs child <ul><li>In normal standing, a tall adult will have a much larger moment of inertia than a toddler </li></ul><ul><li>Once the centre of gravity moves outside the base of support the body will begin to fall </li></ul><ul><ul><li>The adult with the large moment of inertia will fall much more slowly and will therefore have a longer time to react to prevent the fall </li></ul></ul><ul><ul><li>This is one of the reasons that young children fall more often than adults. </li></ul></ul>
  4. 5. Postural control <ul><li>Maintaining static nature of the body </li></ul>
  5. 6. maintenance of posture <ul><li>mainly to maintain the static posture </li></ul><ul><li>necessary for the stability of movements </li></ul><ul><li>involve a set of reflexes </li></ul><ul><li>integrated at spinal cord, brain stem and cortical level </li></ul>
  6. 7. normal postural control <ul><li>three inputs are required </li></ul><ul><ul><li>Vision </li></ul></ul><ul><ul><li>Proprioception (joint position sense) </li></ul></ul><ul><ul><li>Vestibular Mechanism (balance mechanisms) </li></ul></ul>
  7. 9. <ul><li>these reflexes are under higher centre inhibition </li></ul><ul><li>transection of spinal cord or brain stem at different levels release this inhibition </li></ul><ul><li>then the relevant reflexes are seen </li></ul>
  8. 10. spinal cord level
  9. 11. Spinal cord level <ul><li>stretch reflex </li></ul><ul><li>positive supporting reaction (magnet reaction) </li></ul><ul><ul><li>Stimulus: contact with palm or sole </li></ul></ul><ul><ul><li>Response: foot extended to support the body </li></ul></ul><ul><ul><li>receptors: proprioceptors in distal flexors, tactile afferents </li></ul></ul><ul><li>negative supporting reaction </li></ul><ul><ul><li>stretch </li></ul></ul><ul><ul><li>release of positive supporting reaction </li></ul></ul>
  10. 12. Video
  11. 15. spinal cord transection <ul><li>initially a period of spinal shock (2 weeks) </li></ul><ul><li>then followed by appearance of a upper motor neuron lesion features </li></ul><ul><ul><li>spasticity </li></ul></ul>midbrain pons medulla
  12. 16. Spinal shock <ul><li>all spinal reflexes below the level of lesion are completely depressed </li></ul><ul><ul><li>may be due to the sudden cessation of tonic bombardment of spinal cord interneuron pool by descending influences </li></ul></ul>
  13. 17. after the spinal shock <ul><li>reflexes will reappear, mostly exaggerated </li></ul><ul><li>bladder become reflex </li></ul><ul><li>mass reflex </li></ul><ul><ul><li>afferent stimuli irradiate to several reflex centres </li></ul></ul><ul><ul><li>noxious stimulus causes: withdrawal response,evacuation of bladder, rectum, sweating, pallor </li></ul></ul>
  14. 18. medulla level midbrain pons medulla
  15. 19. medulla level <ul><li>tonic labyrinthine reflex </li></ul><ul><ul><ul><li>Stimulus: gravitational pull </li></ul></ul></ul><ul><ul><ul><li>Response: contraction of limb extensors </li></ul></ul></ul><ul><ul><ul><li>receptors: vestibular organs </li></ul></ul></ul><ul><ul><ul><li>(work through vestibulospinal tract) </li></ul></ul></ul><ul><li>tonic neck reflexes </li></ul><ul><ul><ul><li>Stimulus: turning of the head </li></ul></ul></ul><ul><ul><ul><li>Responses: </li></ul></ul></ul><ul><ul><ul><ul><li>turning to a side: extension of ipsilateral limb </li></ul></ul></ul></ul><ul><ul><ul><ul><li>turning up: lower limbs flex </li></ul></ul></ul></ul><ul><ul><ul><ul><li>turning down: upper limbs flex </li></ul></ul></ul></ul><ul><ul><ul><li>receptors: neck proprioceptors </li></ul></ul></ul>Video Video
  16. 21. tonic neck reflexes
  17. 22. tonic neck reflexes
  18. 23. tonic neck reflexes
  19. 24. tonic neck reflexes
  20. 25. tonic neck reflexes
  21. 26. transection of brain stem at superior border of pons <ul><li>decerebrate rigidity </li></ul>midbrain pons medulla
  22. 27. decerebrate rigidity <ul><li>no spinal shock </li></ul><ul><li>spasticity results in the form of decerebrate rigidity </li></ul><ul><li>tonic reflexes are seen </li></ul><ul><ul><li>tonic labyrinthine reflex </li></ul></ul><ul><ul><li>tonic neck reflexes </li></ul></ul><ul><li>spasticity is mainly found in limb extensors </li></ul><ul><li>these reflexes support the body against gravity </li></ul>
  23. 29. midbrain level midbrain pons medulla
  24. 30. midbrain level <ul><li>righting reflexes are seen </li></ul>video
  25. 31. midbrain level <ul><li>labyrinthine righting reflex </li></ul><ul><ul><ul><li>Stimulus: gravitational pull </li></ul></ul></ul><ul><ul><ul><li>Response: attempt to maintain head level </li></ul></ul></ul><ul><ul><ul><li>receptors: vestibular organs </li></ul></ul></ul><ul><li>neck righting reflex </li></ul><ul><ul><ul><li>Stimulus: stretch of neck muscles </li></ul></ul></ul><ul><ul><ul><li>Response: righting of thorax and shoulders </li></ul></ul></ul><ul><ul><ul><li>receptors: muscle spindles </li></ul></ul></ul><ul><ul><ul><ul><li>eg. A newborn's reflex to turn his trunk and shoulders to the same side his head is turned </li></ul></ul></ul></ul>video
  26. 32. midbrain level <ul><li>body-on-head righting reflex </li></ul><ul><ul><ul><li>Stimulus: pressure on side of body </li></ul></ul></ul><ul><ul><ul><li>Response: righting of head </li></ul></ul></ul><ul><ul><ul><li>receptors: cutaneous receptors </li></ul></ul></ul><ul><li>body-on-body righting reflex </li></ul><ul><ul><ul><li>Stimulus: pressure on side of body </li></ul></ul></ul><ul><ul><ul><li>Response: righting of body </li></ul></ul></ul><ul><ul><ul><li>receptors: cutaneous receptors </li></ul></ul></ul>
  27. 33. transection of brain stem at superior border of midbrain <ul><li>righting reflexes </li></ul>midbrain pons medulla
  28. 34. <ul><li>rigidity is seen only when animal lies on its back </li></ul><ul><li>otherwise animal will try to right itself </li></ul><ul><li>righting reflexes (labyrinthine, neck & body) </li></ul><ul><li>grasp reflex may be seen </li></ul><ul><li>pupillary light reflexes are present </li></ul><ul><li>nystagmus is seen </li></ul>
  29. 35. cortical level midbrain pons medulla cortex
  30. 36. cortical level <ul><li>optical righting reflex </li></ul><ul><ul><ul><li>Stimulus: visual cues </li></ul></ul></ul><ul><ul><ul><li>Response: righting of head </li></ul></ul></ul><ul><ul><ul><li>receptors: visual system </li></ul></ul></ul><ul><li>placing reactions </li></ul><ul><ul><ul><li>Stimulus: visual, cutaneous, proprioceptive cues </li></ul></ul></ul><ul><ul><ul><li>Response: foot placed on a surface to support body </li></ul></ul></ul><ul><ul><ul><li>receptors: various </li></ul></ul></ul>
  31. 37. cortical level <ul><li>hopping reaction </li></ul><ul><ul><ul><li>Stimulus: lateral displacement while standing </li></ul></ul></ul><ul><ul><ul><li>Response: hops </li></ul></ul></ul><ul><ul><ul><li>receptors: muscle spindles </li></ul></ul></ul>
  32. 38. removal of cortex <ul><li>decortication </li></ul>
  33. 39. decortication <ul><li>righting reflexes are present </li></ul><ul><li>temperature regulation & other visceral homeostatic mechanisms integrated at the hypothalamus are present </li></ul><ul><li>rigidity is seen (decorticate rigidity) </li></ul>
  34. 40. postural adjustments vestibular nuclei cerebellum pressure & other receptors neck receptors Retina Occulomotor system vestibular system complex pathways

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