Introducing of Brain
Introducing of Brain
The human brain is perched like a flower on the top of a slender stalk, which in a six-foot man is not quite a yard long. The top three inches of the stalk, a thick white cable of nerve fibres known as the brain stem, lies entirely within the skull and is partly buried by the bulging halves or hemispheres of the brain. The rest of the long stalk, the spinal cord, is a direct continuation of the cable outside the skull.
It runs down through holes in the vertebrae of the spine and ends at the small of the back. Many branches extend from the central stalk, like the roads that feed traffic in and out of a motorway. Through their finest fibres they reach into the remotest places, and into every nook and cranny from the roots of hairs and teeth to the tips of the tocs.
The brain itself is three pounds of “messy substance shut in a dark warm place”—a pinkish grey mass, moist and rubbery to the touch, about the size of a coconut. Shock-absorbing fluid cushions it against bumps, sharp blows and other impacts. It is wrapped in three membranes, including an extra-tough outer envelope, and is set snugly into its crate of bone.
Under the microscope a single brain cell with its fibers may resemble the crown of a tree. Growing out from each branch are smaller branches, and from each of them comes a succession of smaller and smaller offshoots down to the most delicate twig. The brain contains some thirteen thousand million such cells, five times more than the total number of people in the world.
These units form masses of twisted fibers, a tangle which one investigator has called the “cerebral jungle.” Until recently most investigators assumed that nerve fibers occupied fixed positions or at least moved only as they grew, like the roots of plants.But New studies indicate that brain tissue is far more active than this. As you read his sentence, fibers in your head are swaying like swept by tides .Tentacles of protoplasm are slowly moving forward, retreating, swelling and shrinking, waving from side to side.
What is the brain for?
Judging by what we know today, it is the great organ of adjustment. It plays the basic biological role of keeping us adjusted to unpredictable events in the outside world, of preserving our identities in an environment of swift and ceaseless chemical change.
The brain keeps us alive by balancing the processes of birth and decay. These basic reactions have top priority. Everything else either helps in carrying them out, or else waits its turn. We pay a high price when the balance of any vital process is upset. For example, sugar is one of the body’s energy providing substances and we must have just the right amount, no more and no less. We walk a biological tight-rope between coma and convulsion, the possible results of relatively slight changes in blood sugar levels.
But the brain usually receives advance notice of impending trouble. It receives a steady flow of information about current sugar levels, and makes adjustments as effectively as a pilot guiding an aeroplane through a storm. If there is too much sugar, the sus is burnt up and excreted. If there is too little, the liver is instructed to release the proper amount of reserve sugar. Notice what such control implies. The brain must “know” the desired sugar level, about a sixtieth of an ounce for every pint of blood, on age, It must go by similar standards in regulating breath
of us inhale and exhale eighteen to twenty times a in hole and heartbeat rates (about seventy times a minute), and ng body temperature at 98.4 Fahrenheit.
They must also be in constant communication with all the parts of the body. Indeed, its function is to act as the headquarters most elaborate communications network ever devised.
Its activities are the result of the combined and patterned activities of millions of nerve cells. A nerve cell is a living wire which produces and conducts rapid electrical impulses. It keeps itself “loaded” and ready for action with the aid of a built in battery which runs on an oxygen-sugar mixture and recharges automatically. It fires—that is, emits up to several hundred impulses a second when triggering impulses reach it from sense organs from other nerve cells.
These outside signals enter the body of the cell through special receiving fibers which are usually short, fine and highly branched. The slenderest fibers, about 1/25,000 of an inch in diameter, have speed limits of a foot a second or two thirds of a mile an hour. But in large gauge fibers, which are about ten times thicker, nerve impulses flash along at speeds up to 150 yards a second, a respectable 300 miles an hour.
Thick, fast fibers generally connect remote parts of the nervous system; thin, slow fibers connect neighbouring regions. Thus, if a cell communicates with several other cells at varying distances, the messages all tend to arrive at about the same time. This means that widely scattered parts of the nervous system can be stimulated, inhibited or alerted at once-a distinct advantage in co-ordinating very complex behavior.
The brain uses this network to adjust us to the outside world.
- Generally speaking, its operation can be divided into three parts:
- (1) it receives input in the form of messages from the sense organs;
- (2) it organizes the input on the basis of past experience, current events and future plans;
- (3) it selects and produces an appropriate output, an action or series of actions.
The brain keeps in constant touch with the flow of events. It is stirred up by lights, sounds, odours and other disturbances in the environment. Each sensation produces electrical impulses in nerves leading to the brain, “shocks” which stream into higher nerve centers and cause cell after cell to fire in a series of chain reactions.
The sense organs most remote from your brain are those loca in your toes. Fibers originating in these outlying stations carry messages concerning heat, cold, muscle tension, touch and pain.
They are joined by more and more fibres from your foot, leg, knee and thighs.
By the time the collected fibbers reach the lower part of the lower part of the spinal cord they form a thick cable. The cable continues to thicken as its climbs and is joined by millions of fibbers from other organs of the body on the way up to the brain. It subjects the brain to constant prodding. Although its lines are less busy during sleep, even then the brain is occupied with various duties keeping your heart and lungs going, dreaming, and listening with a somewhat reduced vigilance. The brain does relax, but as long as it is alive it finds no rest.
Brain and Organs
The brain’s informers are sense organs, sentinels located at strategic points throughout the body. Embedded in the skin are some 3,000,000 to 4,000,000 structures sensitive to pain, 500,000 touch or pressure detectors, more than 200,000 temperature detectors. These tiny organs plus the ears, eyes, nose and tongue are some of your windows to the outside world. Reports about the state of things inside your body come from other built-in sense organs which give rise to sensations of muscular tension, hunger, thirst, nausea.
The brain has other sensory maps. On the cortex at the back of the head are visual maps, screens made up of a mosaic of nerve cells. Every pattern you see about you, every tree and building and face, produces patterns on these screens as various cells in the mosaic. Other sensory fibers lead to the smell areas of the cortex, which are buried deep down in the walls of the chasm between the cerebral hemispheres. Each sense thus has its map on the Cortex, its exclusive zone in the highest center of the nervous system. In this way, the brain sorts the information upon which its activities are based.
In nerve messages, as in dot-dash telegraph codes, patterns of pulses stand for the items of information being sent. But the interpretation of nerve signals depends first of all on the place they arrive at. No matter how accurately senses how meaningful the signals are, they will be misinterpreted if they arrive at the wrong place. A happy-birthday telegram means just that, even if it should happen to reach the wrong person. But a slip-up in the nervous system is something else again.
Suppose you were listening to fast music and nerve signals somehow got switched to the wrong line, arriving at the areas of the visual areas of the cortex instead of the hearing areas. You’d see music as a mad rush of flashing lights, moving forms, vivid colours. Such mix-ups actually occur, and may result from “cross talk’’ between nerve fibers. Cross talk is familiar to telephone repair man If insulation wears off neighbouring wires in a telephone cable electricity leaks away and you may find yourself listening to someone else’s conversation.
Similar leaks in the nervous system may account for many peculiar sensory disorders. Current escaping from a touch fiber to a near by sound fiber, for example, might make you hear crashing noises when you bumped your elbow. Somehow certain drugs increase cross talk among sensory fibers, and nerve injuries may produce the same effect.
There is no reason to doubt that a certain amount of crosstalk takes place in the normal nervous system; the nerve signals travelling through neighbouring fibers interact in some way. We do not yet know the significance of this effect. But new evidence indicates that cross talk between fibers of the right and left eyes have something to do with the mechanism whereby we see objects as three dimensional solids… )
The brain is continually adjusting and readjusting the tensions of many muscles so that you maintain your posture and balance. Simply standing up represents an acrobatic feat which is no less remarkable because it is performed automatically. Everyone naturally sways a bit in an upright position, and a failure in the balance-controlling centers of the brain would send you sprawling.
There is one powerful muscle which, if uncontrolled, would snap your leg back at the knee, pressing your calf hard against your thigh. Another muscle would keep your leg stiff as a ramrod. The brain receives messages specifying the tensions of more than two hundred pairs of opposing muscles, every one of which must be properly adjusted to keep you standing.
Things become more complicated during a walk over uneven ground-and even more complicated when you dive from a high board, lower a sail in a storm or ride a surf board. Every action, Sever simple, is made up of many individual muscle contractions and large scale movements. These movements must follow one another at just the right time and in just the right order. The brain does the timing. It co-ordinates all sequences of movements so that we move smoothly and not in a series of jerks. When it comes to pursuing the activities of everyday life, we are thus reasonably sure of ourselves and our positions in the world.
The hand, working under the direction of the brain, is capable of an unlimited variety of skilled manipulations. A master pianist can play a dozen notes a second with one hand. One famous surgeon used to put a piece of silk thread in a match box and impress reporters with the following trick. Working within the cramped space of the half-closed match-box, he nonchalantly tied the thread into complicated surgical knots using only the thumb, index and middle fingers of his left hand.
Every set of coordinated movements, from such highly skilled performances to routines like walking and driving a car, involve the integrating powers of the nervous system. All activities direct or indirect, successful or unsuccessful are attempts to keep the fire of life burning steadily and as long as possible. And this includes all our attempts to understand life itself.
Our adjustments are never perfect. Things are too complex and too uncertain for that. Still, we do not and cannot stop trying, and the brain coordinates our continuing efforts.
JOHN PFEIFFER
Introducing of Brain Introducing of Brain Introducing of Brain Introducing of Brain Introducing of Brain