Reflex action

Word reflex derived from latin word refluxes which means bending back.

Reflex action can be defined as a quick or immediate response towards stimulus. It is also called involuntary or automatic response because it occurs without the involvement of brain. Here the response is stereotyped means response to same stimulus are always similar.

 There are two types of reflex action:

1)      SIMPLE OR UNCONDITIONAL REFLEX ACTION: Simple reflexes are inborn or unlearned.

              Eg:  Secretion of saliva in mouth seeing sweet or sour food.

             Closing of eyes when an object approaches.

           Sudden withdrawl of body part which comes in contact with object that are extremely hot, cold or        pointed.

2)      CONDITIONAL OR COMPLEX REFLEX ACTION: When a response brought about by learning or experience without the involvement of brain it comes under the category of conditional reflex action.

Eg: Ringing a bell


Mechanism of Reflex Action:

A reflex mechanism involves a receptor organ, an effector organ, sensory and motor neuron. The message travels out of the spinal cord along a motor neuron to the effector organ which shows the response. Reflex refers to a behavior that is mediated via reflex arc.



Reflex arc is the route followed by nerve impulse to produce reflex act from the peripheral organ through afferent nerve to the Central Nervous System (C.N.S.) and then through efferent nerve to effector organ. It is followed by such route:

                                                      Sensory organ


                                                     Sensory neuron


                                                         Spinal cord                  

                                                          Motor neuron

                                                           Effector organ


Reflex arcs can be classified according to the degree of complexity of neuron organization within the reflex arcs:

Monosynaptic (Monosegmental neuron): Sensory neuron has single synaptic connection with motor neuron.

Relay neuron (Association neuron): It makes synaptic connection with nerves that pass upwards into the association areas of brain.

If the controlling center of the reflex arc is located in the brain it is called cerebral reflex. If it is located in the spinal cord, it is called spinal reflex.

The reflex arcs are of two types:

1) Somatic reflex arc involving effector organs located in (soma) body structures.

 e.g. skeletal muscles.

2) Visceral reflex arc involves effectors located in the visceral organs.

 e.g. glands or smooth muscles.

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