Motor system1 reflexes

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Motor system1 reflexes

  1. 1. Reflexes Prof. Vajira Weerasinghe Dept of Physiology
  2. 2. What is a reflex? <ul><li>Response to a stimulus </li></ul><ul><li>Stimulus Response </li></ul><ul><li>Task: </li></ul><ul><ul><li>Write down 3 reflexes . </li></ul></ul>
  3. 3. What is a reflex? Stimulus Effector organ Response Central connections Efferent nerve Afferent nerve Receptor
  4. 4. Stretch reflex <ul><li>This is a basic reflex present in the spinal cord </li></ul><ul><li>Stimulus: muscle stretch </li></ul><ul><li>Response: contraction of the muscle </li></ul><ul><li>Receptors: stretch receptors located in the muscle spindle . </li></ul>
  5. 6. skeletal muscle <ul><li>two types of muscle fibres </li></ul><ul><ul><li>extrafusal </li></ul></ul><ul><ul><ul><li>normally contracting fibres </li></ul></ul></ul><ul><ul><li>intrafusal </li></ul></ul><ul><ul><ul><li>non contractile fibres present inside the muscle spindle </li></ul></ul></ul><ul><ul><ul><li>lie parallel to extrafusal fibres </li></ul></ul></ul><ul><ul><ul><li>contains stretch receptors . </li></ul></ul></ul>
  6. 7. Extrafusal fibre Intrafusal fibre
  7. 8. Contractile areas Stretch receptor
  8. 9. Nerve supply Sensory to intrafusal fibre: Ia afferent II afferent Motor: to extrafusal fibre  motor neuron to intrafusal fibre  motor neuron .
  9. 10. Ia afferent nerve  motor neuron one synapse muscle stretch muscle contraction Stretch reflex
  10. 11. <ul><li>When a muscle is stretched </li></ul><ul><li>stretch receptors in the intrafusal fibres are stimulated </li></ul><ul><li>via type Ia afferent impulse is transmitted to the spinal cord </li></ul><ul><li> motor neuron is stimulated </li></ul><ul><li>muscle is contracted </li></ul><ul><li>Monosynaptic </li></ul><ul><li>Neurotransmitter is glutamate </li></ul>
  11. 12. Stretch Reflex
  12. 13. Stretch Reflex - Knee Jerk
  13. 14. <ul><ul><li>nuclear bag fibre </li></ul></ul><ul><ul><ul><li>primary (Ia) afferent </li></ul></ul></ul><ul><ul><ul><ul><li>supplies annulospiral ending in the centre </li></ul></ul></ul></ul><ul><ul><li>nuclear chain fibre </li></ul></ul><ul><ul><ul><li>primary (Ia) and secondary (II) afferent </li></ul></ul></ul><ul><ul><ul><ul><li>supplies flower spray ending . </li></ul></ul></ul></ul>two types of intrafusal fibres
  14. 15. Ia afferent fibre II afferent fibre nuclear bag fibre nuclear chain fibre  motor neuron  motor neuron
  15. 16. Importance of stretch reflex <ul><li>detects muscle length and changes in muscle length . </li></ul>
  16. 17.  motor neuron <ul><li>cell body is located in the anterior horn </li></ul><ul><li>motor neuron travels through the motor nerve </li></ul><ul><li>supplies the intrafusal fibres (contractile elements at either end) . </li></ul>
  17. 18.  motor neuron  motor neuron  motor neuron
  18. 19. <ul><li>When  motor neuron is active </li></ul><ul><ul><li>extrafusal fibres are contracted </li></ul></ul><ul><ul><li>muscle contracts </li></ul></ul><ul><li>when  motor neuron is active </li></ul><ul><ul><li>intrafusal fibres are contracted </li></ul></ul><ul><ul><li>stretch receptors are stimulated </li></ul></ul><ul><ul><li>stretch reflex is activated </li></ul></ul><ul><ul><li>impulses will travel through Ia afferents </li></ul></ul><ul><ul><li>alpha motor neuron is activated </li></ul></ul><ul><ul><li>muscle contracts . </li></ul></ul>
  19. 20. at rest muscle stretched active  motor neuron Ia Ia  Ia afferents are stimulated stretch reflex is initiated .
  20. 26.  motor neuron activity <ul><li>active all the time - mild contraction </li></ul><ul><li>Maintain the sensitivity of the muscle spindle to stretch </li></ul><ul><li>modified by the descending pathways </li></ul><ul><li>descending excitatory and inhibitory influences </li></ul><ul><li>sum effect is generally inhibitory in nature . </li></ul>
  21. 27. Alpha gamma co-activation <ul><li>gamma motoneurons are activated in parallel with alpha motoneurons to maintain the firing of spindle afferents when the extrafusal muscles shorten </li></ul>
  22. 28. Inverse stretch reflex <ul><li>When the muscle is strongly stretched </li></ul><ul><li>Golgi tendon organs are stimulated </li></ul><ul><li>Via type Ib afferents impulse is transmitted to the spinal cord </li></ul><ul><li>inhibitory interneuron is stimulated </li></ul><ul><li> motor neuron is inhibited </li></ul><ul><li>muscle is relaxed . </li></ul>
  23. 29. Undue stretch Golgi tendon organ muscle relaxation Inverse stretch reflex  motor neuron Ib afferent nerve inhibitory interneuron
  24. 30. Undue stretch Golgi tendon organ muscle relaxation Inverse stretch reflex  motor neuron Ib afferent nerve inhibitory interneuron
  25. 31. Inverse Stretch Reflex
  26. 32. Importance of inverse stretch reflex <ul><li>detects muscle tension . </li></ul>
  27. 33. Deep tendon reflexes (DTR) <ul><li>Biceps jerk </li></ul><ul><li>Triceps jerk </li></ul><ul><li>Supinator jerk </li></ul><ul><li>Knee jerk </li></ul><ul><li>Ankle jerk </li></ul><ul><li>Jaw jerk </li></ul>
  28. 34. <ul><li>reflex level </li></ul><ul><li>biceps jerk C56 </li></ul><ul><li>supinator jerk C56 </li></ul><ul><li>triceps jerk C78 </li></ul><ul><li>knee jerk L34 </li></ul><ul><li>ankle jerk S12 </li></ul>Spinal cord level of stretch reflexes (tendon jerks)
  29. 35. Withdrawal Reflex <ul><li>Stimulus: </li></ul><ul><ul><li>cutaneous stimulation (usually noxious) </li></ul></ul><ul><li>Response: </li></ul><ul><ul><li>withdrawal of the hand </li></ul></ul><ul><li>Polysynaptic reflex . </li></ul>
  30. 36. Withdrawal Reflex
  31. 37. muscle contraction Withdrawal reflex cutaneous receptors polysynaptic
  32. 38. muscle contraction Withdrawal reflex cutaneous receptors
  33. 39. Withdrawal Reflex
  34. 40. Reciprocal innervation <ul><li>inside the spinal cord </li></ul><ul><ul><li>anatagonistic muscles are reciprocally innervated </li></ul></ul><ul><ul><li>stimulation of flexor muscles </li></ul></ul><ul><ul><li>inhibition of extensor muscles . </li></ul></ul>flexor extensor +++ ----
  35. 41. Reciprocal Innervation
  36. 42. Withdrawal Reflex Flexor & Crossed extensor reflex
  37. 43. Withdrawal Reflex
  38. 44. Superficial abdominal reflexes <ul><li>light scratch of the abdominal skin </li></ul><ul><li>brisk unilateral contraction of the abdominal wall </li></ul><ul><li>upper motor neuron lesion causes reduced or loss of these reflexes </li></ul>
  39. 45. Flexor plantar reflex <ul><li>Scratching the sole of foot </li></ul><ul><li>Plantar flexion </li></ul><ul><li>Normal response </li></ul>
  40. 46. Primitive reflexes <ul><li>These are reflexes present in newborn babies but disappear as the child develops </li></ul><ul><li>They were evolutionarily primitive in origin </li></ul><ul><li>In adults these reflexes are inhibited by the higher centres </li></ul>
  41. 47. Babinski sign <ul><li>when outer border of the sole of the foot is scratched </li></ul><ul><li>upward movement of big toe </li></ul><ul><li>fanning out of other toes </li></ul><ul><li>also called extensor plantar reflex </li></ul><ul><li>feature of </li></ul><ul><ul><ul><li>upper motor neuron lesion </li></ul></ul></ul><ul><ul><ul><li>seen in infants during 1st year of life (because of immature corticospinal tract) </li></ul></ul></ul>
  42. 48. positive Babinski sign
  43. 49. Other primitive reflexes <ul><li>Moro reflex; startle reaction </li></ul><ul><li>Walking/stepping reflex </li></ul><ul><li>Sucking reflex </li></ul><ul><li>Tonic neck reflex </li></ul><ul><li>Palmar grasp reflex </li></ul>video
  44. 50. Clinical Importance of reflexes (tendon jerks) <ul><li>Locate a lesion in the motor system </li></ul><ul><li>To differentiate upper motor neuron lesion from a lower motor neuron lesion </li></ul>

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