The human brain is made up of three basic parts: the cerebrum, the cerebellum, and the brain stem.
The cerebrum, the largest part of the brain, makes up the largest portion of the brain's total weight and is divided into two hemispheres—one on each side of the head. The cerebrum is the area in which the body's most complex mental and sensory functions are controlled—memory, intelligence, reasoning, emotions, vision, and our ability to feel things.
The cerebral cortex is the extensive outer layer of gray tissue that covers the cerebrum and is responsible for higher thinking skills.
The cerebellum, a smaller part of the brain, is behind the cerebrum and plays a vital role in coordination, posture and balance.
The brain stem is the part of the brain that connects the cerebral hemispheres to the spinal cord and is responsible for controlling many basic bodily functions, such as breathing, blood pressure, and waking and sleeping.
When the brain is damaged, there are levels of injury—a continuum which encompasses slight memory loss all the way to brain death.
Unconsciousness and its various levels constitute severe brain injury.
Coma: "A coma is a deep state of unconsciousness during which an individual cannot react to his environment," says Dr. James C. Grotta, professor of neurology at the UT Medical School at Houston. "That person is still alive, but he is not 'just asleep.' A sleeping person can be awakened. A comatose patient cannot. The brain wave activity is quite different in each of these cases." It is not unusual for a person in a coma to recover to some degree, he says.
Persistent Vegetative State: Patients in PVS have lost the neurological functions associated with thought, learning and reasoning, but are still able to breathe and go through wake-sleep cycles, Grotta says. Though they are not aware of their surroundings, they can open their eyes, or turn their heads. They may show movements and facial expressions, but neurologists believe those to be reflexes only and not connected to thought or emotion. A person can live for years in a vegetative state.
Researchers believe that one of the important physiological processes that maintain a person's consciousness is the transfer of chemical signals from the brain stem to the cerebral hemispheres of the brain. This continuous neurotransmission needs to occur in order for a person to be aware of his/her environment. Abnormalities that interrupt it can lead to coma, PVS, or other states of unconsciousness.
UPDATED: 4-06-2005
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Dr. James Grotta holds the Roy M. and Phyllis Gough Huffington Distinguished Chair in Neurology at UT Medical School.
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Men who bike more than three hours a week should be aware that standard bicycle seats, ridden for extended periods, can cause temporary numbness and, in some, more serious problems, such as erectile dysfunction.
Such problems are caused by compression of an artery and a nerve connected to the penis. New seat designs to minimize compression are now available.
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