The brain is 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 one, even if diffuse neural tissue is present. It is located in the head, usually close to the primary sensory organs for such senses as vision, hearing, balance, taste, and smell. The brain of a vertebrate is the most complex organ of its body. In a typical human the cerebral cortex (the largest part) is estimated to contain 15–33 billion neurons, 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 either by generating patterns of muscle activity or by driving 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.
From a philosophical point of view, what makes the brain special in comparison to other organs is that it forms the physical structure that generates the mind. As Hippocrates put it: "Men ought to know that from nothing else but the brain come joys, delights, laughter and sports, and sorrows, griefs, despondency, and lamentations." Through much of history, the mind was thought to be separate from the brain. Even for present-day neuroscience, the mechanisms by which brain activity gives rise to consciousness and thought remain very challenging to understand: despite rapid scientific progress, much about how the brain works remains a mystery. The operations of individual brain cells are now understood in considerable detail, but the way they cooperate in ensembles of millions has been very difficult to decipher. The most promising approaches treat the brain as a biological computer, very different in mechanism from electronic computers, but similar in the sense that it acquires information from the surrounding world, stores it, and processes it in a variety of ways.
This article compares the properties of brains across the entire range of animal species, with the greatest attention to vertebrates. It deals with the human brain insofar as it shares the properties of other brains. The ways in which the human brain differs from other brains are covered in the human brain article. Several topics that might be covered here are instead covered there because much more can be said about them in a human context. The most important is brain disease and the effects of brain damage, covered in the human brain article because the most common diseases of the human brain either do not show up in other species, or else manifest themselves in different ways.
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... were divided as to whether the seat of the soul lies in the brain or heart ... Aristotle favored the heart, and thought that the function of the brain was merely to cool the blood ... the "father of medicine", came down unequivocally in favor of the brain ...
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... He studied the instrument under Aubrey Brain, father of Dennis Brain ... In 1955, Civil joined the Philharmonia himself, becoming principal horn player when Brain died in a car crash in 1957 ...
... For instance, in African countries, the health systems have been severely affected by brain drain, so various measures have been suggested and tried to limit the migration of health workers to rich countries ... have argued the country should cultivate a sense of security and hope among the elite to curb brain drain because people are not so confident of their countries' future ... And in India, although suffering severe brain drain every year, the Indian government has not to adopted strict policies because they believe that the overseas talent will eventually ...
Famous quotes containing the word brain:
“Let every woman ask herself: Why am I the slave of man? Why is my brain said not to be the equal of his brain? Why is my work not paid equally with his? Why must my body be controlled by my husband? Why may he take my labor in the household, giving me in exchange what he deems fit? Why may he take my children from me? Will them away while yet unborn? Let every woman ask.”
—Voltairine Decleyre (18661912)
“In the beginning was the secret brain.
The brain was celled and soldered in the thought”
—Dylan Thomas (19141953)
“An honest fellow enough, and one that loves quails, but he has not so much brain as ear-wax.”
—William Shakespeare (15641616)