The Brain and Spinal Cord together form the Central Nervous System, with Twelve Cranial Nerves passing on each side from the Brain and thirty-one nerves from the Spinal Cord, called the Peripheral Nervous System (PNS).
While a complex chain of Nerves and Ganglia lying within the Chest and Abdomen, and acting to a large extent independently of the other two systems, though closely connected with them, make up the Autonomic Nervous System (ANS), and govern the activity of the Viscera.
The Cerebrum: forms the great bulk of the Brain and consists of two Hemispheres which occupy the entire vault of the Cranium and are incompletely seperated from each other by a deep median cleft, the Longitudinal Cerebral Fissure.
The Corpus Callosum: is a thick band of more than 200 million transverse nerve fibers, which is the only connection between the Hemispheres of the Cerebrum. It lies at the bottom of the Longitudinal Cerebral Fissure.
The outer 3mm or thereabouts of the Cerebral Hemispheres consists of Gray Matter largely made up of Ganglion Cells.
While in the deeper part the White Matter consists of Myelinated Nerve Fibers connecting different parts of the surface and passing down to the lower parts of the Brain.
Among the White Matter lie several rounded masses of Gray Matter, the Lentiform and Caudate Nuclei.
In the center of each Cerebral Hemisphere is an irregular cavity, the Lateral Ventricle, each of which communicates with that on the other side and behind with the Third Ventricle through a small opening, the InterVentricular Foramen, or Foramen of Monro.
The Basal Ganglia (Nuclei) consists of two large masses of Gray Matter imbedded in the base of the Cerebral Hemispheres. Between these two masses lies the Third Ventricle.
From which the Infundibulum, which projects downwards into the Pituitary Body, and above lies the Pineal Gland. This region lies above the important HypoThalamus.
The MidBrain or Mesencephalon, is a stalk about 20mm long connecting the Cerebrum with the Hindbrain. Down its center lies a tube, the Cerebral Aqueduct, or Aqueduct of Sylvius, connecting the Third and the Fourth Ventricles.
Above this aqueduct lie the Corpora Quadrigemina, and beneath it are the Crura Cerebri, strong bands of White Matter in which important nerve fibers pass downwards from the Cerebrum.
The Pons is a mass of nerve fibers, some of which run crosswise and others are the continuation of the Crura Cerebri (Cerebral Peduncles) downwards.
The Cerebellum lies towards the back, underneath the Occipital Lobes of the Cerebrum.
The Medulla Oblongata is the lowest part of the brain, in structure resembling the Spinal Cord, with White Matter on the surface and Gray Matter in its interior.
This is continuous through the large opening in the Skull, the Foramen Magnum, with the Spinal Cord. Between the Medulla, Pons, and Cerebellum lies the Fourth Ventricle of the Brain.
The Brain is made up of Gray Matter and White Matter. In the Cerebrum & Cerebellum the Gray Matter is arranged mainly in a layer on the surface, though both have certain Gray Masses imbedded in the White Matter.
In the other parts, the Gray Matter is found in definite Masses called Nuclei, from which the Nerves spring.
The Gray Matter consists mainly of cells in which all the activities of the Brain begin.
These Cells vary considerably in size and shape in different parts of the Brain, though all give off a number of Processes, some of which form Nerve Fibers.
The Cells on the surface of the Cerebral Hemispheres, for example, are very numerous, being set in layers five or six deep. In shape these Cells are Pyramidal, giving off processes from the Apex, from the Center of the Base, and from various projections elsewhere on the Cell.
The Gray Matter is everywhere penetrated by a rich supply of Blood Vessels and the Nerve Cells and Blood Vessels are supported in a fine network of fibers, known as Neuroglia.
The White Matter consists of nerve fibers, each of which is attached, at one end, to a cell in the Gray Matter, while at the other end, it splits up into a tree like structure round another Cell in another part of the Gray Matter in the Brain or Spinal Cord.
The Fibers have insulating sheaths (Myelin)of a fatty material, which in mass, gives the White Matter its color.
They convey messages from one part of the Brain to the other (Association Fibers), or grouped into bundles, leave the Brain as Nerves, or pass down into the Spinal Cord, where they end near and exert a control upon Cells from which in turn spring the Nerves to the body.
Both Gray and White Matter are bound together by a felt work called Neuroglia. The general arrangement of fibers can be best understood by describing the course of a Motor Nerve Fiber.
Arising in a cell on the surface in front of the Central Sulcus, such a Fiber passes inwards towards the center of the Cerebral Hemisphere, the collected mass of fibers as they lie between the Lentiform Nucleus and Optic Thalamus being known as the Internal Capsule.
Hence the Fiber passes down through the Crus Cerebri, giving off various small connecting Fibers as it passes downwards.
After passing through the Pons it reaches the Medulla, and at this point crosses to the opposite side (Decussation Of The Pyramids).
Entering the Spinal Cord, it passes downwards to end finally in a series of branches which meet and touch (Synapse) similar branches from one or more of the Cells in the Gray Matter of the Cord.
The maximum mass of Brain tissue is reached at the age of 20, and then steadily decreases. The Cerebrum is associated with Intellectual Faculties and also exerts a guiding influence over the rest of the Nervous System.
However, it is not necessary for actual life. The Cerebellum maintains Balance, is concerned with the Regulation of Muscular Movements and in preserving the Equilibrium of the Body.
Between 1820 and 1840 it became established that in people who have lost the power of Speech during life, the Brain shows some disease in the Left Frontal Lobe after death.
In 1861 Broca made the first definite discovery in Cerebral localization by proving that the faculty of speech is governed by a center in the region of the Inferior Frontal Gyrus named (after him) Broca's Convolution.
His discovery was followed later by the important observation of Hughlings Jackson that certain forms of Epilepsy, associated with movements beginning in a definite limb are caused by disease affecting the part of the Brain that borders on the Central Sulcus.
This discovery was confirmed and extended by many experimenters and physicians. Grunbaum and others have shown that definite areas near the Central Sulcus are associated with the movement of definite parts.
The Occipital Lobes are associated with the Sense of Sight. The Temporal Lobes with Hearing and the Inner Surface of the same Lobe with the Senses of Taste and Smell.
The purely Intellectual Faculties are probably associated with The Frontal Lobes, which seem to govern nothing else.