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.
Other articles related to "brain":
... 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 ... 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 contribute to the nation ...
... Neuroscience and brain imaging has shown increasing potential for helping science understand happiness and sadness ... findings that depression can be diagnosed very accurately just by looking at fMRI brain scans ... by identifying neural correlates for emotions, scientists may be able to use methods like brain scans to tell us more about all the different ways of being "happy" ...
... He studied the instrument under Aubrey Brain, father of Dennis Brain ... was engaged by Thomas Beecham to play second horn to Dennis Brain in the Royal Philharmonic Orchestra, and when Brain left for the Philharmonia, Civil took. 1955, Civil joined the Philharmonia himself, becoming principal horn player when Brain died in a car crash in 1957 ...
... philosophers were divided as to whether the seat of the soul lies in the brain or heart ... favored the heart, and thought that the function of the brain was merely to cool the blood ... Hippocrates, the "father of medicine", came down unequivocally in favor of the brain ...
... capital flight, more commonly referred to as "brain drain", is the large-scale emigration of a large group of individuals with technical skills or knowledge ... Brain drain is usually regarded as an economic cost, since emigrants usually take with them the fraction of value of their training sponsored by the government or other organizations ... Brain drain is often associated with de-skilling of emigrants in their country of destination, while their country of emigration experiences the draining of skilled individuals ...
Famous quotes containing the word brain:
“It is more than likely that the brain itself is, in origin and development, only a sort of great clot of genital fluid held in suspense or reserved.... This hypothesis ... would explain the enormous content of the brain as a maker or presenter of images.”
—Ezra Pound (18851972)
“The within, all that inner space one never sees, the brain and the heart and other caverns where thought and feeling dance their sabbath.”
—Samuel Beckett (19061989)
“So immense are the claims on a mother, physical claims on her bodily and brain vigor, and moral claims on her heart and thoughts, that she cannot ... meet them all and find any large margin beyond for other cares and work. She serves the community in the very best and highest way it is possible to do, by giving birth to healthy children, whose physical strength has not been defrauded, and to whose moral and mental nature she can give the whole of her thoughts.”
—Frances Power Cobbe (18221904)