Brain test

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The brain - the main organ of central nervous system most chord, its cephalic end; in vertebrates it is inside the skull. The anatomical nomenclature of vertebrates, including humans, the brain as a whole is most often referred to as the encephalon - Latinized form of the Greek word; originally Latin cerebrum has become synonymous with the big brain (telencephalon).
The brain consists of a large number of neurons, linked by synaptic connections. Interacting through these connections, neurons form electrical impulses that control the activity of the whole organism.
Despite progress in the study of the brain in recent years, much of his work still remains a mystery. The functioning of individual cells is well explained, but an understanding of how the interaction of thousands and millions of neurons in the brain functions as a whole, only available in a very simplified form and requires further in-depth studies.
The brain - the main department of the central nervous system. Talking about the presence of the brain in the strict sense it can only be applied to vertebrates, since the fish. However, somewhat loosely, the term used to refer to similar structures of highly organized invertebrates - so, for example, the insects 'brain' is sometimes called cluster peripharyngeal ganglia nerve ring.

brain weight as a percentage of body weight is in modern 0,06-0,44% of cartilaginous fish, bony fish at 0,02-0,94%, tailed amphibians at 0,29-0,36%, tailless 0 50-0,73%. In mammals, the relative brain size is much greater, in large cetaceans of 0.3%; from small cetaceans - 1.7%; primates 0,6-1,9%. In humans, the ratio of brain weight to body weight on average is 2%.
The largest has dimensions of the brain of mammals cetaceans, proboscidians primates. The most complex and functional brain is considered to be the brain of Homo sapiens.
The brain is enclosed in a solid shell of the skull. In addition, it is covered with shells (Latin meninges.) Of connective tissue - hard (lat. Dura mater) and soft (lat. Pia mater), between which is a vascular or arachnoid (Latin arachnoidea.) Shell. Between the shell and the brain and spinal cord surface is cerebrospinal (often it is called spinal) fluid - cerebrospinal fluid (lat liquor.). Cerebrospinal fluid is also contained in the ventricles of the brain. The excess of this fluid is called hydrocephalus. Hydrocephalus can be congenital (usually) and acquired.
The brain of higher vertebrates consists of a number of structures: the cerebral cortex, basal ganglia, thalamus, cerebellum, brainstem. These structures are interconnected by nerve fibers (conductive path). The part of the brain consisting mainly of cells called the gray matter of the nerve fibers - white substance. White color - the color of myelin substance coating fibers. Demyelination fibers leads to serious disturbances in the brain (multiple sclerosis).