| Revision as of 16:33, 8 March 2004 edit62.49.16.208 (talk) gms -> g (also do not agree with phrasing of "weighs only 50 g when suspended in CSF")← Previous edit | Revision as of 18:56, 8 March 2004 edit undoBird (talk | contribs)957 edits reverted plagiarized material. did not realize it was plagiarized when first posted. Also, brain image was copyrighted.Next edit → | ||
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| ''The accuracy of this article has been questioned'' | ''The accuracy of this article has been questioned'' | ||
| In the ] of ]s, the '''] ]''' is the center of the human nervous system. | |||
| ] | |||
| In the ] of ]s, the '''] ]''' is the most complex computational structure developed among all species on ]. Humans' unique capacity for ] ] results both from a larger brain size typical of a larger animal, and from ], which is an increase of brain size in relation to body size. | |||
| ==Overview== | |||
| Human encephalization is especially pronounced in the ]. The human brain not only is larger in proportion to the human body than brains of other animals of the same size; much more of the human brain is neocortex than in other animals. Profound capacities for language, planning, extended memory, empathy and fabrication all can be related to structural features of enlarged ]s that form about a third of the neocortex. In humans, the ], ] and ] make up a smaller proportion of the brain than those of older species. | |||
| Humans enjoy unique neural capacities, but much of the human neuroarchitecture is shared with ancient species. Basic systems that alert the nervous system to stimulus, that sense events in the environment and that monitor the condition of the body are similar in some ways to those of the most basic ]s. Human consciousness involves both the extended capacity of the modern neocortex in particular as well as profoundly developed protypical structures of the ]. | |||
| ==Anatomy== | |||
| The adult human brain usually weighs about 1 - 1.5 kg in an average volume of 1,600 cm³. | |||
| A bulbuous ] is formed of convoluted ] internally supported by deep brain ] and separated by a prominant ]. A well-developed ] is visible at the back of the brain. Brain stem structures are almost completely enveloped by the cerebellum and telencephalon, with the only the ] visible as it merges with the ]. | |||
| The blood supply to the brain involves several arteries that enter the brain and communicate in a circle called the ]. Blood is then drained from the brain through a ] that drain into the right and left ]s. | |||
| The brain is suspended in ] (CSF) which also fills spaces called ] inside it. The dense fluid protects the brain and spinal cord from shock; a brain that weights 1,500 g in air weighs only 50 g when suspended in CSF. (Livingston, 1965). Fluid movement within the brain is limited by the ], ] and the ]. | |||
| The brain is easily damaged by compression, so the fluid surrounding the central nervous system must be maintained at a constant volume. Humans are estimated to produce about 500 ml or more of cerebrospinal fluid each day, with only about 15 percent of the body's estimated 150 ml of CSF at any given time located in the ventricles of the brain. The remainder fills the subarachnoid space which separates the soft tissues of the brain and spinal cord from the hard surrounding bones (skull and vertebrae). Elevated levels of CSF are associated with ] and a ] disease know as ]. Increased fluid pressure can result in permanant brain injury and death. | |||
| ==Function== | |||
| The human brain is the seat of cognitive processes related to perception, interpretation, imagination and memory, of which a person might or might not be aware. Beyond cognitive functions, the brain regulates autonomic processes related to essential body functions such as respiration and heartbeat. | |||
| Extended neocortical capacity allows humans extensive control over ]al behavior, but neural pathways between emotive centers of the brain stem and cerebral motor control areas are shorter than those connecting complex cognitive areas in the ] with incoming sensory information from the ]. Powerful emotional pathways can modulate spontaneous emotive expression regardless attempts at cerebral self-control. Emotive stability in humans is associated with planning, experience and an environment that is both stable and stimulating, especially during early developmental years. | |||
| The ] discovery of a primary motor control area mapped to correspond with regions of the body led to popular belief that the brain was organized around a ]. A distorted figure drawn to represent the body's motor map in the pre-frontal cortex was popularly recognized as the brain's homonculus, but function of the human brain is far more complex. | |||
| The human brain appears to have no localized center of conscious control. Like the brains of other vertebrates, it derives ] from interaction among numerous systems within the brain. Executive decision-making functions rely on cerebral activities, especially those of the ], but redundant and complementary processes within the brain result in a diffuse assignment of executive control that can be difficult to attribute to any single locale. | |||
| Mid-brain functions include routing, selecting, mapping and cataloguing information, including information perceived from the environment and information that is remembered and processed throughout the cerebral cortex. ] functions housed in the mid-brain play a leading role in modulating arousal of the cortex and of autonomic systems. | |||
| Voluntary muscular movements are transmitted through neural networks of the cerebrum to ], as part of a complex feedback system that regulates movement. Complex muscle movements such as a series of notes played on a keyboard or a series of footsteps can be initiated as a packaged concept from the cognitive functions of the cerebral cortex to be executed as a series of steps with the help of the ]. | |||
| Nerves from the brain stem complex where autonomic functions are modulated join nerves routing messages to and from the cerebrum in a bundle that passes through the ] to related parts of a body. Twelve ], including some that inervate parts of the head, follow pathways from the ] outside the ]. | |||
| A definite description of the biological basis for consciousness so far eludes the best efforts of the current generation of researchers. But reasonable assumptions based on observable behaviors and on related internal responses have provided the basis for general classification of elements of consciousness and of likely neural regions associated with those elements. Researchers know people loose consciousness and regain it, they have identified partial losses of consciousness associated with particular neuropathologies and they know that certain conscious activities are impossible without particular neural structures. | |||
| Correlation of particular conscious activities with likely neural structures suggest three levels of consciousness in humans. A ] represents the most basic level of consciousness shared with animals as primitive as amoeba. A ] similar to that of other vertebrates lets humans see and hear their environment. An ] allows us to develop profound narratives describing our own lives and environment. | |||
| ==Related topics== | |||
| * ] | |||
| * ] | |||
| * ] | |||
Revision as of 18:56, 8 March 2004
The accuracy of this article has been questioned
In the anatomy of animals, the human brain is the center of the human nervous system.