1. REFLEX
DR. SARAN AJAY
DEPT. OF PHYSIOLOGY, GMCM
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2. DEPT. OF PHYSIOLOGY, GMCM 3
Specific Learning Objectives
• Reflex
• Reflex Arc
• Classification of Reflex
• Stretch Reflex
• Inverse Stretch Reflex
• Reciprocal Innervation
• Withdrawal Reflex
• Properties of Reflexes
• Summary
DEPT. OF PHYSIOLOGY, GMCM

3. The sudden and involuntary response to a stimuli is
called a reflex.
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4. • It is a mechanism by which a sensory impulse is
automatically converted into a motor effect through
the involvement of CNS.
• It is mediated at the subcortical level and does not
involve the cerebral cortex.
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5. Specific Learning Objectives
• Reflex
• Reflex Arc
• Classification of Reflex
• Stretch Reflex
• Inverse Stretch Reflex
• Reciprocal Innervation
• Withdrawal Reflex
• Properties of Reflexes
• Summary
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DEPT. OF PHYSIOLOGY, GMCM

6. The basic unit of an integrated reflex activity is the
reflex arc.
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7. The arc consists of
1. Receptor
2. Afferent neuron
3. Centre – one or more synapses
4. Efferent neuron
5. Effector organ
Afferent Limb
Efferent Limb
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8. Receptor
Effector
Efferent N
Centre
Afferent N
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9. Afferent neuron carries sensory input from receptor
to center.
• Afferent neurons enter the centre in dorsal roots of
spinal nerves or cranial nerves.
• Have their cell bodies in DRG or in homologous
ganglia on cranial nerves.
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10. Centre is the part where connection between afferent
and efferent somatic neurons occur- integrating
region
• One or more synapses
• Generally, in brain or spinal cord.
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11. Efferent nerve transmit motor impulses from center to
effector organ.
• Efferent fibers leave via ventral roots or corresponding
motor cranial nerves.
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12. Bell –Magendie law
The principle that in spinal cord the dorsal roots are
sensory and ventral roots are motor is known as Bell
–Magendie law.
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13. Sensory
Motor
Dorsal Root
Ventral Root
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14. Activity in a Reflex Arc
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15. Activity in the reflex arc starts in a sensory receptor with a
receptor potential whose magnitude is proportionate
to the strength of the stimulus (graded).
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16. Activity in a Reflex Arc
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17. This generates all-or-none action potentials in the
afferent nerve.
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18. Activity in a Reflex Arc
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19. In the CNS, the responses are again graded in terms of
EPSPs and IPSPs at the synaptic junctions.
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20. Activity in a Reflex Arc
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21. All-or-none action potentials are generated in the
efferent nerve.
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22. Activity in a Reflex Arc
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23. When these reach the effector, they again set up a graded
response, the end plate potential.
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24. Activity in a Reflex Arc
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25. Specific Learning Objectives
• Reflex
• Reflex Arc
• Classification of Reflex
• Stretch Reflex
• Inverse Stretch Reflex
• Reciprocal Innervation
• Withdrawal Reflex
• Properties of Reflexes
• Summary
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DEPT. OF PHYSIOLOGY, GMCM

26. Classification of Reflex
1. Depending on the number of synapses between
afferent and efferent neurons
a. Monosynaptic Reflex
b. Bisynaptic Reflex
c. Polysynaptic Reflex
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27. a. Monosynaptic Reflex Arc
• Simplest reflex arc
• Single synapse between afferent & efferent neurons
• e.g. stretch reflex
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28. DEPT. OF PHYSIOLOGY, GMCM 29
Monosynaptic Reflex

29. b. Bisynaptic or Disynaptic reflex
• Two synapses between afferent and efferent neuron
• e.g. Inverse stretch reflex , reciprocal innervation
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30. DEPT. OF PHYSIOLOGY, GMCM 31
Bisynaptic Reflex

31. c. Polysynaptic reflex arc
• Reflex arc in which one or more interneurons are
interposed between afferent and efferent neurons
• Number of synapses in the arc vary from 2 to many
hundreds.
• e.g. Withdrawal reflex
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32. DEPT. OF PHYSIOLOGY, GMCM 33
Polysynaptic Reflex

33. a. Monosynaptic
• Stretch Reflex
b. Bisynaptic Reflex (2 synapses)
• Inverse Stretch Reflex, Reciprocal Innervation
c. Polysynaptic Reflex (upto 100 synapses)
• Withdrawal Reflex, Superficial Reflexes
e.g.
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34. 2. Clinical Classification
a. Superficial Reflexes – elicited by stimulating skin or
mucus membrane. e.g.
Conjunctival Reflex
Corneal Reflex
Abdominal Reflex
Plantar Reflex
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35. b. Deep reflexes – basically stretch reflexes, elicited by
striking tendon of muscle
• cause stretching of the muscle
• results in contraction of the same muscle
e.g. biceps jerk, knee jerk, ankle jerk
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36. c. Visceral Reflex
e.g.
• Baroreceptor reflex
• Micturition reflex
• Defecation reflex
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37. d. Pathological Reflexes
Reflexes found only in pathological states
e.g.
Babinski’s sign (extensor plantar response)
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38. 3. Based on development
a. Unconditioned / Inborn – present at the time of birth
b. Conditioned /Acquired reflex – develops after birth,
acquired by training or experience
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39. Specific Learning Objectives
• Reflex
• Reflex Arc
• Classification of Reflex
• Stretch Reflex
• Inverse Stretch Reflex
• Reciprocal Innervation
• Withdrawal Reflex
• Properties of Reflexes
• Summary
DEPT. OF PHYSIOLOGY, GMCM 40
DEPT. OF PHYSIOLOGY, GMCM

40. Stretch Reflex
• When a skeletal muscle with an intact nerve supply is
stretched, it contracts.
• This response is called the stretch reflex.
• Sense organ – muscle spindle
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41. • Muscle spindle is a small encapsulated spindle like
structure located within fleshy part of muscle.
• Intrafusal muscle fiber- send information to CNS about
muscle length or rate of change of length.
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42. Muscle spindle
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43. 1. Stimulus - stretch of the muscle
2. Sense organ / receptor - muscle spindle (intrafusal)
3. Afferent nerve – group Ia fibre
4. Centre – spinal cord (alpha motor neuron)
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44. 5. Efferent nerve – axons of alpha motor neuron
6. Effector organ – extrafusal muscle fibres
7. Effect- contraction of same muscle
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45. Stretch Reflex is an example of monosynaptic reflex.
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46. • Typical example – Knee jerk
• Tapping on patellar tendon
(Quadriceps muscle) with a
knee hammer stretches the
muscle
• Response – extension of knee
• Centre - L2, L3 and L4
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47. Stretch reflex circuit for knee jerk
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48. Reaction time
The time between the application of stimulus and the
response.
For knee jerk , it is 19 – 24 milliseconds
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49. This includes
• Time taken for impulse to traverse the afferent and
efferent fibers –Conduction time
• Central delay –Time taken for reflex activity to traverse
the spinal cord
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50. Conduction time can be calculated from
• Conduction velocity in Afferent and Efferent fibers
• Distance from muscle to spinal cord
• V= L/t
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51. Central Delay is 0.6-0.9 milliseconds for knee jerk
Central Delay = Reaction Time – Conduction Time
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52. • Minimum synaptic delay – 0.5 milliseconds
• So in knee jerk, 1 synapse could have been traversed
• Hence knee jerk is a monosynaptic reflex.
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53. Other examples of stretch reflex- deep tendon reflexes
1. Biceps jerk
2. Triceps jerk
3. Supinator Jerk
4. Ankle jerk
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55. Function of stretch reflex
1. Muscle spindle regulate the muscle length.
2. Stretch reflex helps to maintain muscle tone and
posture.
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56. Specific Learning Objectives
• Reflex
• Reflex Arc
• Classification of Reflex
• Stretch Reflex
• Inverse Stretch Reflex
• Reciprocal Innervation
• Withdrawal Reflex
• Properties of Reflexes
• Summary
DEPT. OF PHYSIOLOGY, GMCM 57
DEPT. OF PHYSIOLOGY, GMCM

57. Inverse Stretch Reflex
• Up to a point, the harder a muscle is stretched, the
stronger is the reflex contraction.
• However, when the tension becomes great enough,
contraction suddenly ceases and the muscle relaxes.
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58. This relaxation in response to strong stretch is called the
inverse stretch reflex or autogenic inhibition.
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59. • Stimulus – Strong stretch of the muscle
• Sense organ / receptor – Golgi Tendon Organ
• Afferent nerve – group Ib fibre
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60. • The Ib fibers enter the spinal cord through dorsal root ,
synapse with an inhibitory interneuron.
• It in turn terminate directly on the motor neuron
supplying the same muscle and causes relaxation of
the muscle.
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62. Inverse stretch reflex is an example of bisynaptic reflex.
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63. Inverse stretch reflex - protective reflex to prevent
tearing of the muscle or avulsion of the tendon from its
attachments to bone.
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64. Specific Learning Objectives
• Reflex
• Reflex Arc
• Classification of Reflex
• Stretch Reflex
• Inverse Stretch Reflex
• Reciprocal Innervation
• Withdrawal Reflex
• Properties of Reflexes
• Summary
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DEPT. OF PHYSIOLOGY, GMCM

65. • When we stretch the protagonist muscle, it will contract
through the stretch reflex pathway.
• The afferent neuron give a collateral which synapse
with an inhibitory interneuron.
Reciprocal Innervation
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66. That in turn inhibit the motor neuron supplying the
antagonist muscle producing relaxation of antagonist
muscle.
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67. DEPT. OF PHYSIOLOGY, GMCM 68

68. Reciprocal innervation is an example of bisynaptic reflex.
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69. DEPT. OF PHYSIOLOGY, GMCM 70
Specific Learning Objectives
• Reflex
• Reflex Arc
• Classification of Reflex
• Stretch Reflex
• Inverse Stretch Reflex
• Reciprocal Innervation
• Withdrawal Reflex
• Properties of Reflexes
• Summary
DEPT. OF PHYSIOLOGY, GMCM

70. Withdrawal Reflex
• Typical polysynaptic reflex
• Also called as nociceptive reflex.
• In response to a noxious stimulation of the skin or
subcutaneous tissues and muscle. e.g. pinprick, heat
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72. • Receptors – Nociceptors, free nerve endings of Aδ & C
fibers
• Response –flexor muscle contraction and inhibition of
extensor muscle.
• Helps the stimulated body part to be flexed and
withdrawn from the stimulus.
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73. Mild stimulus
• Flexor muscle contraction and inhibition of extensor
muscles.
• Part stimulated is flexed and withdrawn from the
stimulus.
• Flexor reflex
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75. Strong stimulus
• Not only flexion and withdrawal of that limb but also
extension of the opposite limb.
• This is called crossed extensor response.
• This is due to irradiation of stimulus and recruitment
of motor units.
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77. Many interneurons are involved in the circuit between
the incoming sensory neuron and the motor neurons of
the opposite side of the cord - responsible for the
crossed extension.
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78. Survival value of withdrawal reflex is difficult to demonstrate
in normal animals , but can be easily demonstrated in spinal
animal. (Sherrington)
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79. When the hind limb of a spinal cat is pinched
• the stimulated limb is withdrawn
• the opposite hind limb extends
• the ipsilateral forelimb is extended and
• the contralateral forelimb is flexed.
Called as Shifting Reaction.
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80. • This puts the animal in a position to run away from the
offending stimulus.
• This occurs because of irradiation of stimulus and
recruitment of motor units.
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81. Special features of withdrawal response
1. Withdrawal reflex is a protective reflex
Flexion of the stimulated limb gets it away from the
source of irritation, and extension of the other limb
supports the body.
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82. 2. After Discharge
After the painful stimulus is removed, the crossed
extensor reflex has an even longer period of after
discharge than does the flexor reflex.
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83. DEPT. OF PHYSIOLOGY, GMCM 84

84. a. Because of the synaptic delay at each synapse, activity in
the branches with fewer synapses reaches the motor
neurons first, followed by activity in the longer pathways
Prolonged bombardment of the motor neurons from a
single stimulus - prolonged responses.
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85. b. Some of the branch pathways turn back on themselves,
permitting activity to reverberate.
Such reverberating circuits are common in the brain
and spinal cord.
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86. 3. Withdrawal reflex is prepotent
• They block the spinal pathways from any other reflex
activity taking place at the moment.
• This reflex gets priority when we consider other
reflexes occurring at that time
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87. 4. Local sign
• Dependence of the exact response on the location
of the stimulus.
• If the medial surface of the limb is stimulated, the
response includes some abduction, whereas stimulation
of the lateral surface will produce some adduction with
flexion.
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88. DEPT. OF PHYSIOLOGY, GMCM 89
Specific Learning Objectives
• Reflex
• Reflex Arc
• Classification of Reflex
• Stretch Reflex
• Inverse Stretch Reflex
• Reciprocal Innervation
• Withdrawal Reflex
• Properties of Reflexes
• Summary
DEPT. OF PHYSIOLOGY, GMCM

89. 1. Adequate Stimulus
• The quality of the stimulus that triggers a reflex is
generally very precise and is called the adequate
stimulus for the particular reflex.
• e.g. stretch of the muscle is the adequate stimulus for
stretch reflex.
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90. 2. Final Common Pathway
• The motor neurons that supply the extrafusal
fibers in skeletal muscles are the efferent side of
many reflex arcs.
• All neural influences affecting muscular contraction
ultimately funnel through them to the muscles.
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91. 3. One way conduction
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92. 4. Convergence
• Many to one projection.
• Termination of several neurons on one target neuron.
• e.g. many group Ia afferent fibers from muscle spindle
converging on a single α motor neuron.
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95. Divergence
• One to many projection
• Single presynaptic neuron divide into many branches.
• e.g. termination of pain fibers in withdrawal response on
many motor neurons via different sets of interneurons in
the spinal cord.
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97. 4. Occlusion
Response to simultaneous stimulation of two
presynaptic neurons < sum total of response obtained
when they are stimulated separately.
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98. Decrease in response since pre synaptic fibers overlap and
share post synaptic neurons.
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99. 5. Subliminal Fringe
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100. Neurons are in the subliminal fringe if they are not
discharged by an afferent volley, but have their
excitability increased.
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101. 6. Inhibition
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102. 7. Summation
• Spatial Summation
• Temporal Summation
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104. 8. Habituation
• Progressive decrease of the amplitude or frequency of
a motor response to repeated sensory stimulation.
• Not caused by sensory receptor adaptation or motor
fatigue.
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105. 9. Sensitization
Increased response of the target neuron to an afferent
stimulation, when the previously habituated stimulus is
paired with a noxious stimuli.
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106. Properties of Reflex
1. Adequate stimulus
2. Final common pathway
3. One way conduction
4. Reaction time
5. Summation
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107. 6. Occlusion
7. Subliminal fringe
8. Habituation
9. Sensitization
10.Reciprocal inhibition
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108. 11.Irradiation of stimulus
12.Recruitment of motor units
13.After discharge
14.Local sign
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109. DEPT. OF PHYSIOLOGY, GMCM 110
Specific Learning Objectives
• Reflex
• Reflex Arc
• Classification of Reflex
• Stretch Reflex
• Inverse Stretch Reflex
• Reciprocal Innervation
• Withdrawal Reflex
• Properties of Reflexes
• Summary
DEPT. OF PHYSIOLOGY, GMCM

110. DEPT. OF PHYSIOLOGY, GMCM 111

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112. DEPT. OF PHYSIOLOGY, GMCM 113
Specific Learning Objectives
✓Reflex
✓Reflex Arc
✓Classification of Reflex
✓Stretch Reflex
✓Inverse Stretch Reflex
✓Reciprocal Innervation
✓Withdrawal Reflex
✓Properties of Reflexes
✓Summary
DEPT. OF PHYSIOLOGY, GMCM

113. NEXT CLASS!
saran.adhoc@gmail.com
DEPT. OF PHYSIOLOGY, GMCM 114