The human body is an extremely intricate, divinely computerized and a highly evolved vehicle. It is much like man-made vehicles in that it must be in perfect running condition in order to get a “good performance.”
The nervous system consists of three major parts that must be in a healthy condition in order to work smoothly together. First let’s consider the brain
Brain
The encephalon. That part of the central nervous system contained in the cranial cavity, consisting of the cerebrum, cerebellum, pons and medulla oblongata.
Cerebrum
The chief portion of the brain, occupying the whole upper part of the cranium, and consisting of the right and left hemispheres; the endbrain; telencephalon
Cerebellum
The inferior part of the brain lying below the cerebrum and above the pons and medulla, consisting of two lateral lobes and a middle lobe.
Pons
A convex white eminence situated at the base of the brain. It consists of fibers and nuclei which receive impulses from the cerebral cortex, and sends fibers to the contralateral side of the cerebellum by way of the brachium pontes.”
Medulla oblongata
The upper, enlarged part of the spinal cord, extending from the cord opposite the foramen magnum to the pons.”
The above gives a brief general description of the brain, showing where the various sections lie in the cavity, but let’s go in a little deeper to see how the different sections of the brain work together.
The following information is taken from The New Modern Home Physician, (Wm. H. Wise and Co., Inc., 1947):
- “The large masses of nervous tissue forming the brain has an average weight of forty-nine ounces in a male adult.
- The structure of the brain shows extraordinary complexity.
- The larger part consists of the cerebrum in the form of two hemispheres, right and left, which are connected together by a broad band of fibers running transversely, and known as the corpus callosum.
- Below this come, in succession and on either side, masses of gray nervous matter, the optic thalamus and corpus striatum, and a stalk, the crus, literally a limb.
- Then there is the pons or bridge, and lastly the medulla oblongata or bulb which is continuous with the spinal cord (q.v.).
- Behind and below the cerebral hemispheres is the cerebellum, or little brain, which also consists of two hemispheres. These are connected with each other by a central part called the vermiform process and also through the pons.
Nervous Matter
Nervous matter is of two kinds, gray and white. The former consists of nerve cells and their processes, and the latter of medullated nerve fibers, that is to say, nerve fibers which have a protective white sheath. Both the fibers and the cells are supported by a kind of connective tissue called neuroglia.
The outer surface of the cerebrum and of the cerebellum is composed of layers of gray matter, and this is infolded, forming convolutions, affording thereby an increase in the area of the brain surface.
The optic thalamus, as stated, is composed of gray matter, and besides this there are other masses in the base of the brain, in the crus, the pons and the medulla. It is in the cells of the gray matter that nerve energy originates. The nerve fibers of the white matter merely transmit such energy.
Within the brain there is a series of cavities known as ventricles, which communicate with each other and have a canal that runs down the center of the spinal cord. These are filled with a watery fluid, called the cerebrospinal fluid. The brain is covered by three membranes, the pia mater, in close contact with the brain substance, the arachnoid and the dura mater. The last is in two layers, one lining the interior of the skull, and the other supporting the brain and sending folds into the deep fissures in the brain in order to accomplish this.
The space beneath the arachnoid is filled with cerebrospinal fluid, which is in communication with the fluid in the ventricles of the brain through certain openings at the back of the medulla oblongata. This fact is of importance in connection with the occurrence of hydrocephalus (q.v.). It will be appreciated also that, as a preventive against injury, the brain has the advantage of resting on a water cushion.
The deeper fissures seen on the surface of a cerebral hemisphere mark its division into lobes. The fissure of Rolando (after the Italian anatomist, Lugi Rolando), which, beginning a little behind the top of the head, runs obliquely downwards and forwards, marks the boundary between the frontal lobe in front and the parietal lobe behind. The occipital lobe lies behind the parietal, and below these is the temporal lobe. The mention of these lobes simplifies reference to the functions of the brain. The gray matter on its surface contains millions of nerve cells, which are grouped according to the work they do. In front of the fissures of Rolando is the area concerned with initiating voluntary movements, subdividing into parts serving the leg, arm and face in this order from above downwards. The left side of the brain serves the right side of the body, however, and vice versa.
Sensation is to some extent served by this area, but more by the parietal lobe. Tactile sensations and those of pain and temperature are, however, appreciated by the optic thalamus; but this is under the control of the cerebral cortex or outer surface, and if this control is lost pleasing sensations become more pleasing and painful more painful. In the optic thalamus, also, it would appear that movements expressive of emotion originate, smiling, for example, or grimacing from pain.
The center for hearing is in the temporal lobe, and the smell seems to be related to a part of the brain at the anterior extremity of this lobe. The centers for vision are in the occipital lobe. The speech centers appear to be in the lower frontal and parietal lobes on the left side for a right-handed person. The cerebellum is of importance in preserving equilibrium, and in coordinating the movements of muscles so as to permit the performance of complicated actions.
From the brain comes twelve pairs of nerves, whose names and actions are as follows: (1) olfactory, subserving smell; (2) optic, nerve of vision; (3) oculomotor, supplying most of the muscles which move the eyeball and the muscle which contracts the pupil; (4) nerve supplying the muscle which turns the eyeball downwards and outward; (5) trigeminal, nerve supplying sensation to the face, etc., and to the muscles of mastication; (6) nerve supplying the muscle which turns the eyeball outward; (7) facial, nerve supplying the muscles of the face; (8) auditory, subserving hearing; (9) glossopharyngeal, a nerve of taste, also supplying sensation to the inside of the throat and activating some muscles there; (10) vagus, or wandering nerve, supplying the heart, lungs, stomach and other viscera, etc., (11) spinal accessory, supplying muscles in the neck; (12) hypoglossal, supplying the muscles moving the tongue.
The blood supply of the brain is derived from the internal carotid and the vertebral arteries. The venous blood and cerebrospinal fluid drain into the large venous channels, known as sinuses, which, in turn, pour their contents mainly into the internal jugular vein. At various points on the surface of the skull these sinuses are connected with external veins, which, if they become infected, may communicate infection to the veins within. One of the sinuses, the sigmoid, lies on the inner side of the mastoid process, and not infrequently becomes infected in suppurative disease of the middle ear.
