other neurons. The human brain has more than 15 billion neurons.
brain damage Degeneration or death of nerve cells within the brain that may be centered in one area, causing specific defects, or that may occur in a diffuse pattern, leading to mental problems or severe physical handicap.
Localized brain damage can occur as a result of a head injury or from a stroke, tumor, or brain abscess. It may also be caused by damage to the brain at birth. The basal ganglia may be damaged by carbon monoxide poisoning. Diffuse brain damage is more severe and may be caused by lack of oxygen at birth from cardiac or respiratory arrest or from poisoning, drowning, electric shock, or prolonged convulsions. It may also be caused by toxic substances or environmental poisons, brain infections, or as a rare reaction to immunization.
unlike nerves in the limbs or trunk, nerve cells and tracts in the brain and spinal cord do not recover their function if they have been destroyed. However, there may be some improvement after brain damage as certain parts of the brain take over the function of damaged cells, for the loss. It is not fully understood how this occurs. The ability of a brain-damaged patient to recover depends on the cause and site of the damage and the individual's personality and motivation.
brain death Complete and irreversible cessation of all brain function, usually measured by lack of electrical signals on electroencephalograms taken over a period of at least 12 to 24 hours, even if the heart and lungs continue to function with help from a machine. This time period is important because brain activity may be temporarily depressed by some forms of drug reactions or poisons. If there is a suspicion of intoxication with CENTRAL NERVOUS SYSTEM DEPRESSANTS, the diagnosis of brain death cannot be made.
Brain dead means the patient cannot breathe spontaneously, has no memory, consciousness, knowledge, thought, touch, sight, or any other sense. The brain is irreparably destroyed and begins to deteriorate.
The concept of brain death does not apply to patients who exist in a persistent vegetative state or to other severe degrees of brain damage. Decisions concerning these patients must be made based on other criteria.
While the legal definition of brain death (also called irreversible coma) may vary from state to state, it is usually taken to mean the absence of reflexes, movements, and independent breathing.
This legal definition may become important when considering whether the patient's organs should be donated and in determining whether or not to turn off a ventilator. Because blood supply to organs is important if they are to be transplanted with the best chance for success, they should be taken after the brain is dead but while the heart and lungs are still functioning.
The American Bar Association, the American Medical Association, the National Conference of Commissioners on Uniform State Laws and the President's Commission for the Study of Ethical Problems in Medicine have proposed a model statute to come up with a more standard definition of death. This proposed statute (called the "uniform determination of death act") says:
An individual who has sustained either (1) irreversible cessation of circulation and respiratory functions or (2) irreversible cessation of all functions of the entire brain, including the brain stem, is dead. A determination of death must be made in accordance with acceptable medical standards.
The concept of brain death has been accepted by the Roman Catholic Church and by those attending the First World Meeting on Transplantation of Organs. In 1972, the American Neurological Association accepted brain death as a definition of death.
brain development in children Research has revealed that the first three years of life are critical in the development of the brain and that there is far more to brain development than luck or heredity. Not only does environment affect how large and how fast a child's brain grows, but it helps direct the actual wiring of the brain's circuitry.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.