1. PHYSIOLOGY OF
REFLEXES

2. Definition
Classification
Characteristics of reflexes
Monosynaptic reflexes
Polysynaptic reflexes
Others

3. Definition
Coordinated
involuntary motor response
initiated by stimulus,
applied to peripheral receptors.

4. • Basic unit of integrated reflex activity is
REFLEX ARC.
it has 5 components :
1. Receptor - muscle spindle ( DTR)
2. Afferent - 1a , II fibers
3. Centre - spinal cord
4. Efferent - motor nerve
5. Effector - extrafusal fibers.

6. Definition
Classification
Characteristics of reflexes
Monosynaptic reflexes
Polysynaptic reflexes
Others

7. Classification of reflexes
REFLEXES
No. of
Functional Conditioned
Clinical Anatomic synapses
classification
classification classification Asynaptic Unconditioned
Flexor
Superficial Monosynaptic
Extensor
Deep Segmental Bisynaptic
Righting
Visceral Intersegmental Polysynaptic
Postural
Pathological Suprasegmental
Withdrawal

8. Clinical classification
• Superficial - stimulating superficial structures
Examples
• Deep – stimulating receptors deep in muscle.
Examples
• Visceral – stimulating receptors in viscera.
Examples
• Pathological – present only during abnormality

9. Anatomic classification
• Segmental – reflex arc pass thru one anatomic
segment . Ex : knee jerk
• Intersegmental – involve > one segment
Ex : crossed extensor response.
• Suprasegmental – involve interaction with
suprasegmental components.
Ex: postural reflexes (head-limb)

10. Number of synapses
• Asynaptic axon reflex
• Monosynaptic stretch reflex
• Bisynaptic reciprocal innervation
• Polysynaptic superficial reflex

11. Functional classification
• Flexor reflexes
• Extensor reflexes
• Righting reflexes
• Postural reflexes
• Withdrawal reflexes

12. Others
• Unconditioned reflexes – inborn or inherent
reflexes .
• Conditioned reflexes – acquired reflexes.
Secretion of saliva when food is kept in mouth is
unconditioned reflex and,
secretion even with thought is ‘conditioned’.

13. Definition
Classification
Characteristics of reflexes
Monosynaptic reflexes
Polysynaptic reflexes
Others

14. MONOSYNAPTIC REFLEXES
• Stretch reflex
• Inverse stretch reflex
• Reciprocal innervation
• Clonus

15. Stretch reflex
• When a skeletal muscle with intact nerve
supply is stretched, it contracts – stretch reflex.
• Stimulus – stretch
• Response – contraction
• Sense organ – muscle spindle

17. Muscle spindle
• Proprioceptor present in skeletal muscle.
• 6-14 muscle fibers - Intrafusal fibers (IFF) - in a
spindle shaped fibrous sheath.
NBF - nuclear bag fibers
NCF – nuclear chain fibers

19. • Afferents : I a and II fibers
I a - from central part of all fibers (annulospiral ends)
II – only from NCF ( flower spray ends )
• Efferent :
gamma fibers to both NBF and NCF.
alpha motor neurons supply extrafusal fibers
I a and gamma 1 – dynamic response
II and gamma 2 – static response

21. Functions of muscle spindle :
• Maintains length of muscle fibers (EFF) at rest
or activity – gives feed back to higher centers
for comparing with intended movement.
• Monitor velocity of muscle contraction.

22. Gamma efferent discharge
• IFF are not strong enough or not plentiful enough
to cause shortening of muscle.
• It causes shortening thru reflex arc (indirectly) –
shortening of IFF – stretch of NBF and 1a aff -
reflex muscle contraction through alpha fibers .
• If muscle is stretched during the gamma
stimulation, additional AP s are stimulated and
rate of discharge of 1a afferents increases .

23. (gamma motor neurons increases sensitivity of
muscle spindle to stretch)
Normally there is increased gamma discharge in
parallel to alpha. Due to this alpha-gamma
linkage, spindle also shortens along with muscle.
Due to this continues response of spindle
through out muscle contraction , the physiologic
oscillation is reduced and muscle contraction is
smoothened.

24. • Factors influencing gamma discharge –
 noxious stimulus of skin
 anxiety
 Jendrassik’s maneuver : strong simultaneous
motor act causes increased gamma discharges and
thru irradiation influences other levels.
when voluntary act precedes by 0.5 sec, jerk
is inhibited (negative reinforcement)

25. Higher centers also influence muscle tone
through influencing gamma efferents – brain
stem nuclei, cerebellum and motor cortex.
Cortex inhibits gamma neurons and
cerebellum facilitates them.

27. Importance of stretch reflex
• Production of muscle tone – “partially contracted
state of muscle”.
• Maintenance of posture – in erect posture gravity
tends to flex hip/knee - this slight initial flexion
stretches the extensor , causing its contraction
reflexly.
due to this man remains standing.
Mainly in anti-gravity muscles
Non fatigueble
Simple reflex arc (short latency)

29. • DTR are monosynaptic reflexes.
• Electrical analogue for DTR is the HOFFMAN’s
reflex or H – reflex,

31. INVERSE STRETCH REFLEX
[Auto inhibition / lengthening reaction / clasp knife
reflex ]
• When a limb is passively flexed, in spasticity, lot of
resistance occurs due to contraction of antagonist
muscle. ( in this muscle, the spindle is activated by
stretch which inturn causes contraction of the same
thru 1a )
• When flexed with force it gives off (clasp knife) .
This is due to activation of GTO of antagonist
muscle.

34. • Impulses from GTO thru 1b afferents – reach
motor neurons supplying same muscle thru an
inhibitory interneuron in b/w ( golgi bottle
organ) . Therefore it relaxes
• GTO detects force of contraction and helps in
preventing tearing of muscle

36. RECIPROCAL INNERVATION
• Stimulation of afferent nerve results in
contraction of agonist muscle with relaxation
of antagonist muscle.
• This is the physiological basis for normal
movements and Crossed extensor reflex

37. CLONUS
• Regular, rhythmic contractions of muscle,
subjected to sudden maintained stretch.
• Mechanism – in UMN lesions, the inhibitory effect
of CST on gamma neurons is lost. So gamma eff
discharges are increased. So, spindles are already
hyperactive

38. • When muscle is stretched passively, bursts of
impulses from them discharges all the motor
neurons at once .
The consequent contraction stops the spindle
discharges, but due to sustained stretch the
spindles are again stimulated and it continues

39. Definition
Classification
Characteristics of reflexes
Monosynaptic reflexes
Polysynaptic reflexes
Others

40. POLYSYNAPTIC REFLEXES
Response with fewer synapses is earlier than with
more synapses (due to synaptic delay)
Some activities reverberate until they become
unable to cause a propagated transsynaptic
response and dies out.
These are common in brain and SC

41. WITHDRAWL REFLEX
• Mechanism is ‘reciprocal innervation’ .
Severe pain leads to crossed extensor
response.
Sherrington pointed out the survival value of it.
 flexion of stimulated limb- is to get away
 extn. Of other limb – to support the body.

44. SUPERFICIAL REFLEXES
• Stimulating areas of skin or mucosa causes
contraction of corresponding muscles due to their
surface origin.
• Corneal / conjunctival reflex
• Abdominal reflex
• Gluteal reflex
• Anal reflex
• Bulbocavernous reflex
• Cremastric reflex
• Plantar reflex

45. • Reflex arc for these reflexes is not definitely
known. It seems to be long and complex –
including many interneurons.
Afferent- carried thru posterior columns and STT
End up - in mid brain, thalamus or fore brain
Efferent – carried down thru CST, or extra
pyramidal tracts – to anterior horn cell.
• In UMN lesions , superficial reflexes lost ( path may
be damaged) and DTR are exaggerated (release
phenomenon)

47. Definition
Classification
Characteristics of reflexes
Monosynaptic reflexes
Polysynaptic reflexes
Others

48. MASS REFLEX
• When central excitatory state is marked, the
excitatory impulses irradiate not only to many
somatic areas of SC , but also to autonomic areas.
• Ex : In chronic paraplegias, mild noxious stimulus
cause – in addition to withdrawal response in all 4
limbs- urination, defecation, sweating and BP
fluctuations

49. • Mechanism – when central inhibitions are
lost, it leads to increased activity through
reverberating circuits (irradiation)
Also due to prolonged effects of sympathetic
mediators.

50. SPINAL SHOCK
• WHEN spinal cord transection is complete , there
is a period immediately after the accident when
all spinal reflexes below the level of transection
are reduced or suppressed.
• Over wks-months , the reflexes gradually return
and are exaggerated.

51. • Mechanism –
(of shock)- sudden withdrawal ,of tonic
facilitatory influences from the brain.
(of recovery) – denervation super-sensitivity
and increased post synaptic receptors.

52. Definition
Classification
Characteristics of reflexes
Monosynaptic reflexes
Polysynaptic reflexes
Others

53. Characteristics of reflexes
• Irradiation • After discharge
• Delay • Fatigue
• Summation • Fractionation
• Occlusion • Reciprocal
• Subliminal fringe innervation
• Facilitation • Rebound
• Recruitment phenomenon

54. Irradiation
• Strong stimulus
• Spread to neighboring neurons producing a
wider response.
• Mechanism – collaterals
Withdrawal response
Crossed extensor response
Mass reflex
Reinforcement

55. Delay
• Total reflex delay / reaction time
• Central delay
• Mechanism – due to synapse
Ex : KNEE JERK - reaction time – 19-24 msec
central delay – 0.6-0.9 msec

56. Summation
• Subliminal stimuli – insufficient response
• Spatial summation – applied simultaneously
• Temporal summation – in series
• Mechanism – persistence of excitability in the
path of reflex arc, which summates with the next.

57. Occlusion
T : tension produced by simultaneous stimulation
of 2 afferents.
t1 : by afferent 1
t2 : by afferent 2
T < t1 + t2
Mechanism : due to common motor nerves shared
by both afferents.

58. t1+t2 T

59. Subliminal fringe
Reverse of occlusion
T > t1+t2
Mech – separate stimuli – inadequate for some
motor neurons ( subliminal )
- simultaneous stimuli – these subliminal
ones get summated.

60. Facilitation
If reflex is elicted repeatedly at proper
intervals, the response becomes progressively
higher .
Mechanism : passage of 1st impulse facilitates the
transmission of next one – by decreasing synaptic
resistance , the next subliminal stimulus becomes
liminal. (facilitation)

61. Recruitment
Direct motor nerve stimulation – tension quickly
rises to maximum.
Sensory afferent stimulation – gradual rise
Mechanism – inteneuron ( ?? )

62. After discharge
After a reflex contraction , if stimulus
discontinued – relaxes gradually ( not at once )
Mechanism – interneuron go on discharging . And
also impulse takes longer time to reach muscle
thru interneuron.

63. Fatigue
If a reflex is elicited repeatedly, it becomes feebler
and disappear.
Mechanism – seat of fatigue is CNS (mainly synapse)
Synapse > motor end plate > muscle.

64. Fractionation
Direct motor N stimulation – higher amount of
contraction , than reflexly thru afferent N
Mechanism – strength of impulse lost while crossing
synapse, so only part of ( fraction of ) motor pool
is stimulated

65. Reciprocal innervation
In a reflex , when protagonists contracts,
antagonists relax to same degree.
Mechanism – bisynaptic – inhibitory interneuron
present.
i afferent – at single joint.
ii, iii, iv - at several joints

67. Rebound phenomenon
(just as muscle is excited , it can also be inhibited
reflexly – reflex inhibition- tone decreased and
muscle elongated)
Following it, if stimulus is stopped – tone is
increased much more , instead of going to normal
resting tone .
Mechanism - ??