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Text B. Conditioned Reflexes
All the visceral and somatic reflexes including the protective, feeding and others are formed by various internal and external stimuli. These stimuli produce reactions not depending on surrounding conditions. The great Russian physiologist Pavlov called them nnconditioned reflexes.
In human beings the nervous system has the additional ability to form cortical associations which increase the range of reactions. This function is obtained by all the human beings and formed upon signalization, ie the process in which an ineffective reflex stimulus forms the same reactions as the stimulus with which it has become associated. Pavlov called these individually obtained reflexes conditioned, because they are developed only in connection with some other reflexes.
It is through constant contacts of life that men develop many conditioned reflexes. They begin to develop already in infancy. During human development their number is much increased through training and education.
In experimental conditions it was determined by Pavlov that many new conditioned reflexes to stimuli not supplied by Nature could be established in dogs. But such stimuli had to be associated with those which formed an unconditioned response. Pavlov determined that in higher animals it was in the cortex that conditioned reflexes were formed.
The nervous cells of the cortex are the most delicate of all the cells of the human body.
It is at the moment of tiredness of the cortical nervous cells that the process of inhibition begins to act. This process does not allow new stimuli to pass to the tired areas of the brain. To provide the smooth work of the brain the nervous cells must be well supplied with oxygen and feeding substances. And for this purpose any human being must have regular complete rest, ie sleep.
When the process of inhibition extends over a great number of cells, spreads widely over the cortex and even over the subcortical areas of the brain one falls asleep.
When one sleeps the vital activity of the nervous system is restored. So sleep is of a great protective significance to the human being.
The man sleeps about one third of his life. Numerous investigations and experiments have shown that sleep is more necessary for the human being than food. One can live longer without food than without sleep.
During a sound quiet sleep the whole activity of the human organism changes, the body metabolism decreases, the respiratory and pulse rates become slower, the body temperature drops. Though the stimuli continue to come into the brain, ....
One of the scientific research institutes in Chechoslovakia carried out an interesting experiment. Six young persons-four men and two girls did not sleep for 124 hours. They were under the constant observation of the doctors who took their cardiograms, determined the pulse and blood pressure and carried out many other investigations.
Not to fall asleep they were allowed to do physical exercises, dance and play, but they were not allowed to take any stimulants. Vision, hearing and various reflexes were often examined during the experiment.
The experiment was successful. Its findings showed that prolonged sleeplessness increased the amount of sugar in the blood, decreased the level (amount) of vitamins B, and B6, produced considerable increase of white blood cells and decreased the amount of iron in the blood.