A reflex action is an automatic and rapid response to a stimulus, which minimises any potential damage to the body. 
It is essential for survival of organisms. 

Reflex actions are therefore RAP:

  • Rapid
  • Automatic
  • Protective

reflex arc diagram

The Pathway:

Let us use the example of someone touching something very hot. 

1) Receptors in the skin detect a stimulus (something hot i.e. change in temperature)

2) The receptors send an electrical signal along the sensory neurone 

3) The sensory neurone then sends these electrical impulses to a relay neurone in the spinal cord

4) The relay neurone connects the sensory neurone to a motor neurone

5) The electrical impulses then travel along the motor neurone towards the an effector muscle

6) The effector muscle produces a movement which is rapid, automatic and protective

7) In this case, the effector muscle moves the hand away from the hot object

Sequence:

Receptor
⬇︎
Sensory Neurone
⬇︎
Relay Neurone
⬇︎
Motor Neurone
⬇︎
Effector Muscle
⬇︎
Response