Motor system1 reflexes

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