Reflexes:

It is of  interest  to know,  that all sensory information does not have to go to the  -  brain before we can react to a stimulus. Our responses to certain stimuli are simple unvaried  and quick. For instance, if  a finger  is  too close to a burning match, receptor cells on the skin send the infarmation on a nerve to  the spinal cord, and a 'reflex action' is taken  to move the  finger away fm  the fire. Such 'reflex drcuits' are well distributed and one is shown in Fig.  

Now  let us see what happens when a pin pricks the finger. 

1  The pin p-rick  is the stimulus which activates a receptor cell at that point. 

2  A nerve impulse  is transmitted away from the skin along a sensory neuron to the spinal cord. 

3  The impulse is now passed  through the inter neuron to the motor neuron and finally passes to the-muscle  which pulls the hand back from the painful event. 

The brain is not normally involved in such simple reflex actions. Only after the event, is the brain informed and we become conscious  of what has happened. The time gap between the stimulus and the response is about 1115^th of a second and this is often crucial for survival. For instance,  a person who is driving a car has to apply his brakes to avoid a sudden collision with another car. His reflex action timing is important if he  ( has to avoid the accident. Similarly,  the reflexes of an airplane pilot have to be fast to avoid disaster. Human capacity to handle equipment and machines is limited by  the time taken by one's  reflexes.