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Brain And Nervous: The fact that direct electrical stimulation of the anterior pituitary does not induce secretions led Harris to search for a further link in the control mechanism. He suggested that the hypothalamus liberates humoral agents into the hypophyseal portal system (a blood vessel system in the pituitary stalk)—an idea later substantiated in many laboratories. After these demonstrations of nervous control of hormonal secretions, Harris investigated hormonal control of nervous activity. Implanting fragments of solidified hormone into the brain and nervous of cats, he located brain and nervous areas that regulate sexual behavior.
The nervous stimuli cause the brain and nervous of the cow to send signals to the pituitary gland at the base of the brain and nervous. The pituitary gland secretes a hormone called oxytocin that is carried through the blood stream to the udder. In the udder, oxytocin acts on the cells and literally forces the milk out into the main ducts. At this time, if the cow is milked immediately and rapidly, all the milk can be easily withdrawn.
Among the most interesting developments in brain and nervous studies was a finding that corrected the long-held conviction that glucose was the only fuel the brain and nervous was capable of using. George Cahill studied brain and nervous metabolism in persons who fasted for more than 30 days as part of a weight reduction program. By sampling blood entering and leaving the head, he was able to show that during fasting the brain and nervous will readily metabolize fatty acids, the breakdown products from deposits of body fat. Careful intelligence tests before and after the fast failed to show any mental impairment during the period of fasting. Cahill said that in fact the subjects were at least as sharp after fasting, and maybe a bit sharper. |
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