1. Definition Classification Properties of Reflex Action

2. Reflex Action Definition
Automatic involuntary motor response to a sensory stimulus based on a reflex arc is called reflex action
The arc consists of an afferent part – receptor ( superficial or deep )and an afferent neurone
Center – usually in the spinal cord or brain stem
Efferent part – efferent nerve and an effector organ – usually a skeletal muscle , may be a muscle – ( smooth, cardiac or skeletal ) or gland ( exo or endocrine ). Usually it is skeletal muscle response which is considered.
Example

3. Classification
1.Based on the number of synapses involved – Monosynaptic – Deep or Stretch reflex –Knee jerk
Disynaptic – negative stretch reflex, reciprocal innervation
Polysynaptic - Flexor or withdrawal reflex
Asynaptic – local axon reflex

4. 2.Based on development – phylogeny
Unconditioned
Present at Birth
Number Few
Due to Existing Reflex arc
Abolished with difficulty, permanent
Function protective, Instinctive
example touching a hot stove
species specific
Predictable
Training not required

5. 2.Based on development – phylogeny
Conditioned reflex
Acquired
Many superimposed easily
some good some bad
Salivation at thought of food
Based on past Experience
on existing arcs
individual specific
Learned
Habits and learning
Unpredictable

6. Classification
3.Based on clinical importance and site of presence of receptors –
Superficial – flexor reflex – Plantar reflex Babinski’s response , conjunctival, corneal and abdominal
Deep – stretch reflex
Visceral – Urinary bladder actions

7. Classification 4.Segments of spinal cord involved
segmental – one segment of same side involved
Intersegmental – segments of both sides or more than one segment involved
Suprasegmental – higher segments involved

8. Classification 5.Depending on the purpose – functional
a.Protective – flexor reflex
b.Postural – antigravity – extensor reflex
c.Righting reflex
d.Conditioned reflex
e.Sexual reflex
f.Locomotor
g.Systemic – CVS, respiratory etc.

9. Classification 6.Response confined to one or more muscle groups
a.Simple –
b.coordinated
c.Convulsive

10. Classification 7.Depending on site of centre a.Spinal b.Bulbar
c.Mesencephalic
d.Diencephalic
e.Cortical

11. Properties of reflex action
Reflex action combines the properties of both synapse and receptors – demonstrated in spinal and better in decerebrate animal. Most of the properties apply to flexor or withdrawal reflexes as there are multisynaptic.

12. Properties of reflex action
1.Specificity – A sensory stimulus always give rise to a specific response – eg. Showing light in to the eye gives rise to constriction of the eye etc .Specificity of the reflex action makes the predictability of the response .However, super imposed conditioned reflexes may mask them

13. Properties of reflex action
2.Synaptic delay – reflex time is the time between the stimulus and response and is dependant on number of synapses and the delay of conducting the impulses across it .

14. Properties of reflex action
3.Unidirectional conduction – Impulses are transmitted in one direction only – from the receptors towards to the center in the sensory and from the centre towards periphery in motor nerves .
4.Excitation – some reflexes are excitatory
5.Inhibition- some reflexes are inhibitory in nature

15. Properties of reflex action
6.Reciprocal Innervation – Muscle contracts reflexly with the contraction of agonist and relaxation of an antagonists . In knee jerk – contraction of extensor of knee is accompanied by inhibition of flexor of the knee.
Basis - due to an inter neuron placed in the reflex arc
branch of the afferent connects to the excitator
(develops EPSP) to the agonist
and another to a Golgi bottle neuron or Renshaw cell neurone which it stimulates .
This in turn inhibits the antagonist by forming IPSP due to release of an inhibitory transmitter to the neuron supplying the antagonists .
This ensures the smooth contraction of the agonist
Diagram

16. Properties of reflex action
7.Irradiation A feeble stimulus gives rise to weak contraction and a strong stimulus gives rise to a strong contraction due to inclusion of adjacent motor neurone .A small pin prick – only finger withdrawn. A bold cut , entire hand is withdrawn.

17. Properties of reflex action
8.Recruitement and after discharge – When a muscle contracts to direct stimulation there is a quick simple muscle twitch.
When it is reflexly contracting instead of quick and short lived contraction, it builds momentum and is sustained with a slow decline.
This is due to recruitment and after discharge .
Basis- Parallel circuits in the reflex arc of varying length.
Diagram

18. Properties of reflex action
9.Rebound – For a short time following the elicitation of a reflex action ,the excitability of the agonist is reduced and that of antagonist is increased.

19. Properties of reflex action
10.Summation – both Spatial and Temporal summations are seen in the reflex actions. When two relax actions give the same effect , elicitation of both of the simultaneously gives a greater response – spatial summation .
When the stimuli are given repeatedly also the response is more. – temporal summation

20. Properties of reflex action
11.Due to convergence and divergence in the reflex pathways subliminal fringe and occlusion are seen similar to synapse )
12.Facilitation
13.Fractionation
14.Fatigue – Repeated elicitation of reflexes leads to reduced response due to fatigue .

21. Functions
1.Major functions of CNS and ANS are reflex in nature. For eg. posture, equilibrium, locomotion, visceral activities.
2.In CNS itself , learned activities may become patterned for reflex performance .For eg.walking – learned becomes a locomotor reflex only command for start and stop are actually voluntary.
Human beings are given the capacity to convert reflex to delibration- intelligence .The response can be stopped, altered , augmented. Brain development ensures that more and more actions come under delibration so that there is coordination and the organism is elevated from lower to higher status ( wisdom )

22. Functions 3.Economy of energy as spinal cord itself takes
care of most of the actions
4.Homeostasis –
5.Clinical application for diagnosis – When elicited with properly- absence indicates LMN lesion and exaggeration UMN Lesion
Role of higher centres . Release phenomenon .
Site of lesion can be located.
Abnormal plantar – Babinski’s – Pyramidal lesion