Ivan Pavlov and the reflexes embedded in the nervous system

Posted in Animals, Biology, Historical articles, History on Monday, 23 April 2012

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This edited article about Ivan Pavlov originally appeared in Look and Learn issue number 693 published on 26 April 1975.

The brain, picture, image, illustration

A pictorial diagram of the brain showing the nervous system

If you accidentally touch something hot, such as a stove, you immediately pull your hand away. You do this because of an automatic movement called a reflex.

You don’t think about the pain you feel and then decide to pull your hand away. Pulling your hand away just happens – long before you are really aware of the fact that you are hurt.

Other examples of reflex action are when your eyes water and you blink your eyelids if a speck of dust blows into the eye.

Reflexes also come into action if a light is suddenly shone at you. The pupils of the eyes immediately become smaller and you automatically close your eyelids.

If you see or smell some very attractive food, reflexes cause your mouth to water. Sometimes reflexes are strong enough to cause mouth watering at the very thought of food!

You do not even need to be awake for reflexes to get to work.

Tickle the sole of a sleeping person’s foot, and he or she immediately pulls the tickled foot away.

Most reflex actions are caused by an impulse which is carried by the nerve of that part of the body touched to a central nerve centre.

From this nerve centre another impulse is sent down to the muscles controlling the limb or other part of the body that was touched and causes it too move.

If it was a limb, it is drawn away. The same happens with the eyelid when the speck of dust blew into the eye.

The nerve centre controlling reflex actions is rather like a telephone exchange. But instead of connecting subscribers, it links the different parts of the body to the brain.

Cross one leg over the other and smartly tap the top leg, just below your kneecap. Your leg will jump as your hand touches it – another example of your “reflexes.” Now do it again – and this time try and “will” your leg not to jump up. You can’t!

Why should this be so?

When you tapped your leg you caused a nerve message to go straight to the muscles which made your leg jump.

More than thirty years ago a famous Russian biologist named Ivan Pavlov found that animals could have completely new reflexes “built in” to them at will.

He kept ringing a bell every time he showed a fat juicy steak to a dog. Saliva immediately started to drip from the dog’s mouth.

Then Pavlov rang the bell without showing the dog a steak. The dog still dribbled saliva from its mouth!

Pavlov had conditioned the dog to show the signs of hunger every time a bell rang.

This is called a conditioned reflex. Conditioned reflexes are the secret of training circus animals.

Performing animals do their tricks not because they “think” about it, but because they respond automatically to the sight of food offered to them during training.

At the same time they hear their trainer’s voice or the crack of a whip.

They will then do their tricks later in the circus ring when only the voice or the whip is heard, without being offered the food!

It is surprising how many of the things which human beings and animals do throughout their lives are done automatically, without the help of any conscious will or effort.

The moment a musician sees a note of music, his finger presses a key on the piano. The bull sees a piece of cloth flutter in the matador’s hands and charges – at the cloth, not its enemy!

When a dog is angered, it bares its fangs and the hair on its back stands on end – another example of automatic reflexes.

Exactly how and where inside animals, these “built-in” mechanisms work is still not clearly understood by biologists.

We do know, however, what can cause them, what “stimulus,” such as light, or heat, or touch, can make the appropriate connections on the nerve switchboard.

And, as Pavlov proved, if reflexes aren’t there to start with, animals can be given “conditioned” reflexes to make them behave in unusual ways.

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