The brain, The Three-pound Miracles | The brain of human being is only a small part of the human body, but it is an extremely important ones. The human brain weighs only about three pounds and looks like a mass of jelly. The volume of the brain is about three pints (in metric units about 500 cubic centimeters [cc]). This is because of pound of water has a volume of one pint, and the brain, like the rest of human body, contains a good deal of water. Yet there is a computer in that three-pound jelly-like mass. The computer in the human brain is more powerful and more complicated that any computer that scientists engineers have been able to build.
Not all animal brains are as large or as complicated as the human brain. All vertebrates (vertebrates are animals with skeletons and backbones) have brains, but their brain are not all the same size. The brain of primitive vertebrate such as fish, frogs, and snakes are much smaller than human brain, and they are tube-like in shape. These tube-like brain have three parts of about equal size: the forebrain, the midbrain and the hindbrain.
Mammals are higher vertebrates which are warm blooded and nurse their young. Some examples of mammals are elephants, deer, dogs, mice and people. They have brain that are somewhat different from the brains of primitive vertebrates. The forebrain is greatly developed in mammals especially a part called the cerebrum. Human beings are mammals, and they have an extremely large cerebrum. This cerebrum is divided into two cerebral hemispheres. (A spare is a round ball, and a hemisphere is half of a spare.) there is a bridge of tissue called corpus callosum between the two hemispheres.
The cerebrum is located in the forebrain. It is the largest and one of the most important part of the brain. However, there are other parts to the forebrain, particularly the group of organs called the limbic system. The human midbrain is small and folded inside the rest of the brain. So it is difficult to see. The hindbrain has two important parts , the medulla,oblongata and the cerebellum . these are at the bottom of rear of the brain, near the place where it is attaches to the spinal cord. There are also a number of small glands located at the brain. The thalamus and hypothalamus are two of these. Another one is a tiny gland called the pineal gland. The French philosopher Rane Descartes thought that it was the place where the body was in contact with the soul. We now think the pineal gland was once a third eye that our reptilian ancestors had millions of years ago. The tuatara, a strange lizard-like animal that lives only in New Zealand, has pineal gland that functions as a third eye. This third eye is able to distinguish light and darkness.
The human brain is a computer (when it is computing we are thinking). It is also a switchboard and command center as well. It receives messages from your eyes, ears, nose and tongue. It also receives impulses telling us when we are touching things. When our body injured, it sends a message of pain to the brain. All the messages go to the brain through the nervous system. The nervous system consists of special cells called nerve cell. Messages and commands are sent from one cell to another by electrical impulses.
The brain itself consists of about 50 billion nerve cell. Each one of these cell is in touch 10.000 other brain cells. From the brain, messages travel out through a part of the nervous system called the spinal cord. The spinal cord consists of many nerve cell which from a long string or fiber inside our backbones (spines). From the spinal cord, nerves travel out to various parts of the body, all the way to the tips of our fingers and toes. The brain sends commands through the nervous system to our muscles and causes us to walk, run, pick something up, shake hands, and so on. Actions like running or picking something up require thinking. We do these things on purpose.
The brain and the nervous system also cause us to do some things without thinking—such as breathing or digesting our food. We do not have to command our brain to do these things. We also do not have to command our hearts to beat because the brain and the nervous system do it for us. Breathing and digesting our food called autonomous functions, and they occur whether ot not we think about them.
Scientists know less about the brain than they do about most other parts of the body. However, they have learned some things about the brain, and in the next two readings you will read about what they have learned.
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