The Brain and Nervous system

The pons, a saddle-like mass of coarse fibers, connects the medulla with the higher brain centers. The medulla, or spinalbulb, just below the pons and at the upper end of the spinal cord, is a switching center for nerve impulses to and from higher brain centers.

 It also contains centers which, as we will see, work through the autonomic nervous system to control heart action, changes in artery walls, breathing, and other activities that go on without our conscious effort. The cerebellum, or little brain, is divided into hemispheres like the cerebrum. The front and back areas control muscle tone. Equilibrium is the concern of an area behind the back lobe. The two main hemispheres coordinate voluntary movements.

It is characteristic of the intricate organization of brain and nervous system that the cerebellum receives nervous messages from the balance mechanism of the inner ears, from the muscles and joints, and from centers deep in the brain, and then sends impulses to the muscles adjusting their tone and coordinating their action. Are you able, with eyes closed, to touch the tip of your nose? Can you both rub your stomach and pat your head simultaneously? Then your cerebellum is still at work.

Protection for the Brain

The brain is an excellent example of built-in protection provided by nature for a vital organ, Despiteprocesses in the brain, brain tissue itself is quite sturdy stuff, tough and resilient. It is protected against injury in a number of ways. A tough bony cage, the skull, surrounds the brain completely. It takes a very strong blow to break the skull. The skull itself is protected by the scalp, which can absorb some tough blows. The scalp is made up of five layers which medical students remember by an acrostic: S is for skin (and hair in which in women constitutes considerable protection), and the skin of the scalp is the thickest in the body; C is for the cutaneous tissue, a layer under the skin; A is for the aponeurosis, a tough layer of fibrous tissue which helps the scalp slide around; L is for some loose tissue;

Still more protection is provided

 Inside the brain are four reservoirs, the ventricles, which contain cerebrospinal fluid. This fluid circulates around the brain. Thus, the brain practically floats on and in fluid. And engineers will tell you that this is an ideal "shock absorber" system. Finally, inside the bone of the skull the brain is wrapped in layers of tissue. One of these layers, the dura mater, is particularly tough and helps protect the brain against blows. But nature cannot provide infinite protection, and it has not foreseen the demands of modern society. It did not anticipate that man would ride motorcycles at 100 miles an hour, and might hurtle over the handle-bars.

Or that children would go out on hard turf and play football. Or those workmen would walk under skyscraper construction projects where a bolt falling from the fortieth floor would develop the speed of anartillery projectile. So we need additional protection: adequate helmets for motorcyclists and athletes, steel hats for workmen exposed to possible head injuries. Parents must realize, too, that babies fall off beds and, at some stage, jump out of cribs. These must be guarded against and a baby doctor can advise. Beyond protecting the brain from injuries, you can protect it so there is no interference with its efficient operation. 

THE BRAIN AND NERVOUS SYSTEM

THE BRAIN AND NERVOUS SYSTEM 

EVERYTHING YOU does in, and every awareness and impression you have of, life is the result of activity in the brain and nervous system. To call it a remarkable system is to understate the obvious. It is so complex that scientists are only making a beginning at penetrating its mysteries. And yet enough has been determined, and it is now possible to understand sufficiently the broad outlines of the makeup and functioning of the system in health and disease, to permit you to do much to preserve its health.

THE BRAIN 

Of all things known in the universe, the human brain is, by far, the most intricate. Although it weighs only about 12 ounces on the average at birth and in an adult only about 3 pounds, its storage capacity is phenomenal. It has been estimated that the brain can store more facts, impressions, and total information than are contained in all the 9 million volumes in the Library of Congress. It's another indication of the brain's complex organization that, if necessary, you can get along with only half of it. The fact is that after removal of much of one side of the brain because of tumor, doctors, lawyers, and others have been able to carryon with their regular work.

And in one study with 62 soldiers who suffered penetrating head wounds during World War II, the men, upon being retested for intelligence, showed little or no change in scores they had made in the Army General Classification Test upon first entering service. Although at various times there has been some belief that the brain is compartmentalized, with specific areas for specific functions, the evidencemany studies is that when some brain area is damaged, another area may be able to take over its functions. 

The brain has 15 billion nerve units which permit storage of memory images and all the learning we accumulate. In addition, it has huge numbers of connections which control the more than 600 muscles in the body. Other connections into the brain from the eyes, ears, and nerves in the skin permit us to record and remember what we see, hear, feel, smell, and taste.

The brain is made up of several parts. 

The cerebrum, largest and most familiar, takes the form of two hemispheres divided by a groove. The surface, or cortex, of the cerebrum is the gray matter we hear about, formed by the cell bodies of nerve cells. Fibers from these bodies lead inward and form the white matter of the cerebrum. Some of these fibers lead to the center of the brain; others extend from front to back and from side to side; and deep in the brain, complicated junctions are formed.

 Actually, most of the fibers cross over so that one entering the brain from the left side of the body crosses to the right side of the brain, which is why the right lobe of the cerebrum controls most of the left side of the body, while the left lobe controls the right side. At the base of the cerebrum are three structures: pons, medulla, and cerebellum.