This document discusses the physiology of reflexes. It defines a reflex as a coordinated involuntary motor response initiated by a stimulus to peripheral receptors. Reflexes are then classified in several ways, including by clinical features (e.g. superficial vs deep), anatomy (e.g. segmental vs intersegmental), number of synapses involved (e.g. monosynaptic), and function (e.g. flexor vs extensor). Key monosynaptic reflexes are then discussed in more detail, including the stretch reflex mediated by muscle spindles, and its role in producing muscle tone and maintaining posture.

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
3. Centre
4. Efferent
5. Effector
- 1a , II fibers
- spinal cord
- motor nerve
- extrafusal fibers.

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

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

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,