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Adrenaline's effects on Reflexes
Reflexes are the ability to act quickly and without conscious thought is called a reflex. Reflexes actually help guide most of the body's work, even when we are asleep.
  One important task of the reflexes is to help the body adjust to changes.
  Adrenaline, a hormone, stimulates the body mechanisms that help us take emergency action. Each receptor responds to one kind of sense impression, such as heat or cold, pressure, or sound. It sends its responsive message, or impulse, through nerve fibers to a motor cell. This cell, in turn, sends an impulse to a muscle or gland, which responds to the original sense impression by some action.
  A simple example of a reflex reaction is the "knee jerk," used by doctors to test the soundness of nerves. If the patient's nerves are sound, he responds with a sudden and uncontrollable kick.   When you exercise violently, the blood uses up oxygen more rapidly than normal. An excess of carbon dioxide accumulates in the blood and is carried to nerve centers.

How Reflexes Are Changed

All reflexes are subject to change. In the human adult most reflex actions are modified; few are pure. The motor paths which carry impulses for the winking reflex also conduct impulses for voluntary winking and closing of the eyelid. We may have an impulse to sneeze and at once inhibit this reflex. The process by which a new connection is established between a stimulus and a reflex is known as conditioning.  
  Famous studies of experimental conditioned reflexes were made by the Russian physiologist, Ivan Pavlov.
After a time the reflex which brought saliva to the dog's mouth at the taste of meat could be started by ringing the bell without giving the animal any meat.

Conditioned Reflexes Influence Habits

Some scientists regard conditioned reflexes as of fundamental importance in human development, especially in child training. They describe habits as consisting merely of patterns or systems of conditioned reflexes. The simple conditioned response, however, differs from an original response and from an established habit in being less regular and permanent.   
The girl's normal reflex from the pain of the bite became conditioned by her mother's excitement so that it resulted in extravagant terror at the mere sight of a spider.   
Disgusted, he threw the apple away and for some time afterward refused to eat apples in any form.