3D-HuBEd No.3 -BRAIN-

The brain is a center of a nervous system and important organ which controls activities of a body, not only conscious and unconscious activities but advanced functions like thinking, memory, feelings and language. The weight of this complex organ which comes of age is only 1.4kg, but includes more than a billion of nerve cells. The brain is largely divided into three parts: a brain stem which controls body functions such as respiration or digestion, a cerebellum which controls motion of a body, a cerebrum which does intellectual activity. In these parts, the cerebrum is especially important. It is divided into two parts: the left and the right cerebral hemisphere. The left consists of a cerebral cortex and the right consists of cerebral medulla. These functions are different in each part.

Refer to chapter 0 for more information on how to use this textbook.

　　3.1 The structure of whole brain
　　3.2 Functions of cerebrum
　　3.3 The basic unit of nerve, synapse

3.1 The strucure of whole brain

The brain and the spinal cord consist of grey matter that has many nerve cells and white matter that is a gathering of nerve fiber. The brain is divided into a cerebrum, a cerebellum, a brain stem. A spinal cord is connected to the medulla oblongata included by brain stem.

The human cerebrum is highly developed and covers the interbrain and the midbrain. It has many gathers and increases its surface area. Adult male's one weighs 1350g and female's one weighs 1250g. It is divided into the left and the right hemisphere by the fissura interhemisphaerica and 2-3 millimeters thick cortex(grey matter) covers the internal marrow (white matter). Three membranes( hard membrane, arachnids membrane, soft membrane) cover outside the cortex. A marrow is a set of nerve fibers which are out from cells. There are basal ganglias which are some cores of nerve cells in the marrow.

Under the cerebrum, a cerebellum sticks to the back side of it and a brain stem extends from the center of it. The brain stem extends to the interbrain, bridge, medulla, oblongata and the spinal cord.

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Functions of cerebru

The cerebrum plays very important parts in human life about consciousness, intelligence, will and memory. As shown before, a cerebrum is divided into the left and the right hemisphere and each consists of the cerebral cortex and the basal ganglia. In the cerebral cortex, each part has its own functions such as language, motions of a body, thinking, feelings and divides the works.

3.2.1 Division of the works by the parts of a cerebral cortex

Since a surface of a cerebral cortex have many big and small complex gathers, the quantity of the surface is more than two thousands square centimeters. There is a cerebral cortex which has most nerve cells in the brain between the bottom of the surface which is 2-5 millimeters thick. The cerebral cortex has 10-14 billions of cells in all. Any part of the left and the right hemisphere of the cerebral cortex does not differ much in the structure, but differs much in the function. For example, about the speech center, there is the Broca motor speech field in the anterior lobe of the cerebrum and the Wernicke auditory speech field in the bottom of a parietal lobe. The right and the left hemisphere also differs in function. For example, a dominant brain of a right-handed person is the left hemisphere. The sense organ of the human peripheral nerve and the area of muscle which controls it is located to project whole body on the cerebral cortex.

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