The Cerebrum is the newest part of the Brain, and that part which is responsible for Higher Mental Function. The Cerebrum is subdivided into Lobes; Four in all, one on each side and Two in the MidLine.

Grossly, the Brain is exactly the same on right and left, while functionally there are differences between the right of the Brain and the left side.

Most Anterior are the Frontal Lobes, next come the Parietal Lobes, and the most Posterior Lobes are the Occipital.

The Temporal Lobe is tucked like the thumb of a mitten into the area just above the Ear. Each of these Lobes has special functions.

The outermost surface of the Brain is composed of Nerve Cells and is called the Cortex. The Processes (Axons) of these Nerve Cells passing upward and downward comprise the White Matter, which is the greatest volume of the Brain.

Deep inside the Brain, just above the BrainStem, are several masses of nerve cells with very important functions.

The most important of these is the Thalamus, which is a way station for relay of messages to the Cortex and has important functions in processing information as well.

Another of these buried areas of Gray Matter is the HypoThalamus, which has important connections in Behavior and in Hormone Function. The third of these areas of nerve cells is called the Basal Ganglia. These cells are very important in coordination of motor movement.

The Cerebrum sits on the BrainStem, and the Cerebellum, especially important in coordination of Motor Movement, is located in the angle between the BrainStem and Cerebrum. The BrainStem has many important functions.

Most of the Cranial Nerves come from the BrainStem, and all of the fiber tracts passing up and down from Peripheral Nerves and Spinal Cord to the higher parts of the Brain must traverse the BrainStem.

The BrainStem is especially important in control of Subconscious and Reflex Activities such as Breathing, Heart Rate and Blood Pressure.

Ventricular System

If the Brain is cut in cross section, it is seen to have Four Cavities within it. Inside the Cerebrum there are Two large Lateral Ventricles that connect in the Midline to the Third Ventricle.

The Third Ventricle is connected by a very narrow passage called the Aqueduct to the Fourth Ventricle, which lies between the BrainStem and the Cerebellum.

Within these Ventricles a structure called the Choroid Plexus is located. The Choroid Plexus produces the CerebroSpinal Fluid, which is a clear, watery fluid that both supports the Brain and provides its Extracellular Fluid.

This fluid circulates through the Ventricles and descends in the Spinal Canal to circulate around the Spinal Cord and the Spinal Nerves, returning upwards to pass over the entire Surface of the Brain and be absorbed into the Veins.
(Also See: Ventricles)

Functional Anatomy

The Frontal Lobes are important in two major areas. The Anterior part of the Fronral Lobe is called the PreFrontal Cortex and is especially important in Highest Mental Function and in the Determination of Personality.

The Posterior part of the Frontal Lobe controls Motor Movement and is divided into a PreMotor and Motor Area. In the Motor Cortex are located the Nerve Cells that actually Produce Movement, and in the PreMotor Area are several portions of the Brain that Modify Movement.

The Frontal Lobe is divided from the Parietal Lobe by the Central Sulcus. Immediately behind the Motor Cortex is the Primary Sensory Cortex.

This controls Sensation, such as Touch, Pressure, Localization of objects that Touch the Skin. Just behind this area is a very large Association Area that controls such fine sensation as Judgement of Texture, Weight, Size, and Shape.

The Occipital Lobe is concerned with Vision. On the Medial Surface of the Lobe is located the Calcarine Cortex, which contains the cells that have to do with Primary Visual Reception.

The rest of the Occipital Lobes are Association Areas that help in the Recognition of Size, Shape and Color.

The Temporal Lobe has numerous functions. The Auditory Cortex is located on the Superior Internal portion of the Temporal Lobe and an area called the Hippocampus forms the Lobe's Medial portion.

This Hippocamus and related structures are very important in behavior. The medial part of the Temporal Lobe is connected to the HypoThalanus and then to the Frontal Lobes, with interconnections to many other parts of the Brain.

On the left side of the Brain in right-handed individuals is located the Speech Area. The Hemishpere containing Speech is called the Dominant Hemisphere.

Motor Speech is located at the base of Frontal Lobe, in Broca's Area. This is the part of the Brain that controls the movement necessary for Speech.

On the Lateral portion of the Lobe there is an important area that has to do with Hearing Speech, and in the base of the Parietal Lobe are Association Areas that have to do with Understanding and Carrying out the Complex Actions required for Speech.

The Brain gets its Primary Blood Supply from the Two Internal Carotid Arteries and the Two Vertebral Arteries.

The Vascular connections at the Base of the Brain form the Circle Of Willis, which is composed of a Vascular loop consisting of the Two Anterior Cerebral Arteries and the Anterior Communicating Artery in front and the Posterior Communicating Artery and the Posterior Cerebral Arteries behind.

There are numerous variations and congenital abnormalities associated with the Circle Of Willis.

The Internal Carotid Artery divides IntraCranially into two main branches. One is the Anterior Cerebral Artery, which passes forward and immediately above the Optic Chiasm to enter the Longitudinal Fissure of the Cerebrum.

It furnishes blood to the major part of the Medial Aspect of the Cerebral Hemisphere and gives off several vital Perforating branches at the base of the Brain that supply blood to the head of the Caudate, the Anterior part of the Lentiform Nucleus, the Internal Capsule, the Anterior Columns of the Fornix, and the Anterior Commissures.

The loss of these important Perforators leads to deep Coma.

The Middle Cerebral Artery is the larger of the two terminal branches of the Internal Carotid Artery and passes laterally through the Sylvian Fissure to the surface of the Insula, where it divides into numerous Parietal and Temporal Cortical branches.

During its course through the Sylvian Fissure it gives off important Perforating Arteries called Medial and Lateral Striate Arteries, which pass upwards through the Putamen of the Lentiform Nucleus, and also supplies blood to the Globus Pallidus and the Internal Capsule.

These arteries that frequently rupture in cases of spontaneous Cerebral hemorrhage are known as the Arteries Of Charcot.

The Vertebral Arteries enter the IntraCranial cavity and transverse the base of the Medulla, giving off two PosteroInferiore Cerebellar Arteries, which supply blood to the BrainStem and the PosteroInferior surface of the Cerebellum.

The Vertebral Arteries then join to become the Basilar Artery. The Perforating branches from the Basilar Artery to the remainder of the BrainStem are vital to many life functions.

The AnteroInferior Cerebellar Artery arises from the Basilar Artery at the Ponto-Medullary junction and gives blood to the AnteroInferior surface of the Cerebellum.

There is frequently an important loop that passes into the internal Auditory Canal from the AnteroInferior Cerebellar Artery and returns to the BrainStem to supply blood to the Pons.

Close to the Basilar summit arises the Superior Cerebellar Artery, which has perforating branches to the BrainStem and to the superior surface of the Cerebellum.

The Posterior Cerebral Arteries are the terminal branches of the Basilar System. They also have extremely important Perforating Central Arteries, which supply blood to the Cerebral Peduncle, the Posterior Perforated Substance, the Posterior part of the Thalamus, and the Mammillary Bodies during their course around the BrainStem.

The Posterior Choroidal branches pass through the upper part of the Choroid Fissure, then to the Posterior part of the Tela Choroidea of the Third Ventricle, and then to the Choroid Plexus.

The Posterior Cerebral supplies Blood to the Uncus, Hippocampal Gyrus, Medial Temporal Lobe, Occipital Lobe and to a small portion of the Posterior Parietal Lobe.

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Cranial Nerves

It arises from numerous Rootlets from the Anterior Portion of the Medulla Oblongata. The Rootlets are arranged in double bundles and unite in the Anterior Condylar Canal, where they emerge from the Cranial Cavity.

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CerebroSpinal Fluid Circulation

Most of the CerebroSpinal Fluid is formed within the Lateral Ventricles of the Cerebrum by the Choroid Plexus.

CerebralSpinal Fluid is a clear, colorless liquid of low specific gravity that in health has between two and three Lymphocytes per cubic millimeter.

Its volume is between 100 and 140 ml in adults, and the normal pressure varies from between 70 and 200 mm of water with the patient on his side.

Total protein in adults varies from 20 to 45 %mg with glucose varying from 50 to 75 %mg. Chlorides are between 120 and 230m eq/lit.

From the Lateral Ventricles, fluid traverses the InterVentricular Foramina into the Third Ventricle.

Here, presumably, the Choroid Plexus of the Third Ventricle contributes fluid, which then passes through the Aqueduct Of Sylvius into the Fourth Ventricle, where further additions are made by the Choroid Plexus in the roof of the Fourth Ventricle.

The fluid then enters into the SubArachnoid Space through a median aperture called the Foramen Of Magendie and lateral apertures called Foramina Of Luschka.

Some fluid passes downward into the Spinal SubArachnoid Space, but the major portion rises through the Tentorial Notch and finds its way slowly over the surface of the Hemispheres to be absorbed mainly through the Arachnoid Villi and Granulations into the Venous System.

There appear to be mechanisms of CSF absorption, mainly through the PeriNeural Lymphatics, and in addition, in abnormal pressure states it appears possible for CSF to be absorbed through the Ependyma.

Each blood vessel, as it enters the Brain tissue, incorporates a Prolongation of the SubArachnoid Space by which CerebroSpinal Fluid can come in contact with the Neurons themselves.

Any obstruction to the Ventricular System, either by blockage of the foramen of Monro, the aqueduct of Sylvius, or of the Foramen of Magendie and Luschka, will create a Non-Communicating type of HydroCephalus, in which the Ventricular System will dilate.

Pressure within the Ventricular System in Hydrocephalus can increase in an acute and fatal manner. If absorption is interfered with there develops a HydroCephalus classified as Communicating.