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The Brain
The Brain Wikipedia
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. Only a few invertebrates such
as sponges, jellyfish, adult sea squirts and starfish do not have a brain; diffuse or localized nerve nets are present instead. The brain is located in the head, usually
close to the primary sensory organs for such senses as vision, hearing, balance, taste, and smell. The brain is the most complex organ in a vertebrate's body. In a
typical human, the cerebral cortex (the largest part) is estimated to contain 15–33 billion neurons,[1] each connected by synapses to several thousand other
neurons. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action
potentials to distant parts of the brain or body targeting specific recipient cells.
Physiologically, the function of the brain is to exert centralized control over the other organs of the body. The brain acts on the rest of the body both by generating
patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows rapid and coordinated responses to changes
in the environment. Some basic types of responsiveness such as reflexes can be mediated by the spinal cord or peripheral ganglia, but sophisticated purposeful
control of behavior based on complex sensory input requires the information integrating capabilities of a centralized brain.
The operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions is yet to be
solved.[2] Recent models in modern neuroscience treat the brain as a biological computer, very different in mechanism from an electronic computer, but similar in
the sense that it acquires information from the surrounding world, stores it, and processes it in a variety of ways, analogous to the central processing unit (CPU) in
a computer
Brain
From Simple Wikipedia, (the free encyclopedia)
The brain is the part of the body which lets us, and other animals, make sense of
the world. It gets input from sense organs, and changes behaviour in response to
this information. In humans, the brain also controls our use of language, and is
capable of abstract thought.[1] The brain is the control center of the whole
body.[2] The brain is made up of a special type of cells. They are connected with
each other and with the nerves in our body. In all animals the delicate brain is
protected in some way. In ourselves, and all vertebrates, it is protected by
the bones of the skull.
Human Brain
The human brain is the main organ of the human central nervous system. It is located in the head, protected by the skull. It has
the same general structure as the brains of other mammals, but with a more developed cerebral cortex. Large animals such as
whales and elephants have larger brains in absolute terms, but when measured using a measure of relative brain size, which
compensates for body size, the quotient for the human brain is almost twice as large as that of a bottlenose dolphin, and three
times as large as that of a chimpanzee, though the quotient for a treeshrew brain is larger than that of a human's.[3] Much of the
size of the human brain comes from the cerebral cortex, especially the frontal lobes, which are associated with executive
functions such as self-control, planning, reasoning, and abstract thought. The area of the cerebral cortex devoted tovision,
the visual cortex, is also greatly enlarged in humans compared to other animals.
The human cerebral cortex is a thick layer of neural tissue that covers most of the brain. This layer is folded in a way that
increases the amount of surface area that can fit into the volume available. The pattern of folds is similar across individuals but
shows many small variations. The cortex is divided into four lobes – the frontal lobe, parietal lobe, temporal lobe, and occipital
lobe. (Some classification systems also include a limbic lobe and treat the insular cortex as a lobe.) Within each lobe are
numerous cortical areas, each associated with a particular function, including vision, motor control, and language. The left and
right sides of the cortex are broadly similar in shape, and most cortical areas are replicated on both sides. Some areas, though,
show strong lateralization, particularly areas that are involved in language. In most people, the left hemisphere is dominant for
language, with the right hemisphere playing only a minor role. There are other functions, such as visual-spatial ability, for which
the right hemisphere is usually dominant.
Despite being protected by the thick bones of the skull, suspended in cerebrospinal fluid, and isolated from the bloodstream by
the blood–brain barrier, the human brain is susceptible to damage and disease. The most common forms of physical damage
are closed head injuries such as a blow to the head, a stroke, or poisoning by a variety of chemicals which can act
as neurotoxins, such as ethanol alcohol. Infection of the brain, though serious, is rare because of the biological barriers which
protect it. The human brain is also susceptible to degenerative disorders, such as Parkinson's disease, and Alzheimer's disease,
(mostly as the result of aging) andmultiple sclerosis. A number of psychiatric conditions, such as schizophrenia and clinical
depression, are thought to be associated with brain dysfunctions, although the nature of these is not well understood. The brain