Brain
In
animals, the brain, or
encephalon , is the control center of the
central nervous system. In most animals, the brain is located in the head, protected by the
skull and close to the primary sensory apparatus of vision, hearing, taste and
olfaction. In humans, it is an organ of
thought. While all
vertebrates have a brain, invertebrates have either a centralized brain or collections of individual
ganglia. Brains can be extremely complex. For example, the
human brain contains more than 100 billion
neurons, each linked to as many as 10,000 others.
Encyclopedia
In
animals, the
brain, or
encephalon , is the control center of the
central nervous system. In most animals, the brain is located in the head, protected by the
skull and close to the primary sensory apparatus of vision, hearing, taste and
olfaction. In humans, it is an organ of
thought. While all
vertebrates have a brain, invertebrates have either a centralized brain or collections of individual
ganglia. Brains can be extremely complex. For example, the
human brain contains more than 100 billion
neurons, each linked to as many as 10,000 others.
Overview
Most brains exhibit a visible distinction between grey matter and white matter. Grey matter consists of the cell bodies of the neurons, while white matter consists of the fibers that connect neurons. The axons are surrounded by a
fatty
insulating sheath called
myelin, giving the white matter its distinctive color. The outer layer of the brain is grey matter called
cerebral cortex. Deep in the brain, compartments of white matter , grey matter and spaces filled with cerebrospinal fluid are found.
The brain innervates the
head through
cranial nerves, and it communicates with the
spinal cord, which innervates the body through
spinal nerves. Nervous fibers transmitting signal from the brain are called efferent fibers. The fibers transmitting signals to the brain are called
afferent fibers. Nerves can be afferent, efferent or mixed .
The brain controls a wide variety of functions. It is the site of reason and intelligence, which include such components as
cognition,
perception, attention,
memory and
emotion. The brain is also responsible for control of
posture and movements. It makes possible cognitive, motor and other forms of
learning. The brain can perform a variety of functions automatically, without the need for
conscious awareness, such as coordination of
sensory systems , walking, and
homeostatic body functions such as
heart rate,
blood pressure, fluid balance, and body temperature.
Many functions are controlled by coordinated activity of the brain and
spinal cord. Moreover, some behaviors such as simple
reflexes and basic locomotion, can be executed under spinal cord control alone.
The brain undergoes transitions from wakefulness to
sleep . These state transitions are crucially important for proper brain functioning. . Each brain state is associated with characteristic
brain waves.
Neurons are electrically active brain cells that process information, whereas
Glial cells perform supporting function. Brain cell metabolism consumes considerable amounts of energy. In addition to being electrically active, neurons constantly synthesise neurotransmitters. Neurons modify their properties under the influence of their input signals. This plasticity underlies
learning and adaptation.
The study of the brain is known as
neuroscience, a field of
biology aimed at understanding the functions of the brain at every level, from the
molecular up to the
psychological.
History
Early human views on the function of the brain regarded it to be a form of “cranial stuffing” of sorts. In Egypt, from the late Middle Kingdom onwards, in preparation for mummification, the brain was regularly removed, for it was the
heart that was assumed to be the seat of intelligence. According to
Herodotus, during the first step of mummification: ‘The most perfect practice is to extract as much of the brain as possible with an iron hook, and what the hook cannot reach is mixed with drugs.’ Over the next five-thousand years, this view came to be reversed; the brain is now known to be the seat of intelligence, although colloquial variations of the former remain as in “memorizing something by heart”.
Mind and brain
A distinction is often made in the
philosophy of mind between the mind and the brain, and there is some controversy as to their exact relationship, leading to the
mind-body problem. The brain is defined as the physical and biological matter contained within the
skull, responsible for all electrochemical neuronal processes. The mind, however, is seen in terms of mental attributes, such as beliefs or desires. Some believe that the mind exists in some way independently of the brain, such as in a soul or epiphenomenon. Others, such as strong AI theorists, say that the mind is directly analogous to
computer software and the brain to
hardware.
Comparative anatomy
Three groups of animals have notably complex brains: the
arthropods , the
cephalopods , and the
craniates . The brain of arthropods and cephalopods arises from twin parallel nerve cords that extend through the body of the animal. Arthropods have a central brain with three divisions and large
optical lobes behind each eye for visual processing. In craniates, the brain is protected by the
bones of the
skull. In vertebrates, increasing complexity in the
cerebral cortex correlates with height on the
phylogenetic and evolutionary tree. Primitive vertebrates such as
fish,
reptiles, and
amphibians have fewer than six layers of neurons in the outer layer of their brains. This cortical configuration is called the allocortex .
More complex vertebrates such as mammals have a six-layered neocortex , in addition to having some parts of the brain that are allocortex.
Consuming the brain and other nerve tissue of animals is not without risks. The first problem is that the brain is made up of 60% fat due to the myelin insulating the axons of neurons and glia. As an example, a 140 g can of "pork brains in milk gravy", a single serving, contains 3500 milligrams of
cholesterol, 1170% of our recommended daily intake.
Brain consumption can also result in contracting fatal transmissible spongiform encephalopathies such as Variant Creutzfeldt-Jakob disease and other
prion diseases in humans and
mad cow disease in cattle. Another prion disease called kuru has been traced to a funerary ritual among the Fore people of
Papua New Guinea in which those close to the dead would eat the brain of the deceased to create a sense of
immortality. Some
archaeological evidence suggests that the mourning rituals of
European
Neanderthals also involved the consumption of the brain.
It is not only humans who eat the brains of other animals. The two species of
chimpanzee, though generally
vegetarian, are known to eat the brains of
monkeys to obtain fat in their diet.
See also
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Further reading
References
External links
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- — Provided by New Scientist is a weekly international [i] science magazine [i] covering recent developments in sci ...
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- , interactive high-resolution digital brain atlas based on scanned images of serial sections of both primate and non-primate brains
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- Pinky and the Brain sing
