Information about the medical term Coma. Part 1!

Coma

A coma is a deep state of unconsciousness, during which an individual is not able to react to his or her environment. Someone in a coma cannot consciously respond to stimulation. Coma can be caused by an underlying illness, or it can result from head trauma. A comatose person is still very much alive, but he or she is not simply asleep. The brain wave activity in a comatose person is very different from that of a sleeping person; you can wake up a sleeping person, you can't wake a person in a coma.

A coma usually does not last for more than a few weeks. Many people recover their full physical and mental functioning when they emerge from a coma. Others require various forms of therapy to recover as much functioning as possible. Some patients never recover anything but very basic body functions.

Sometimes, following a coma, a person may enter what is known as a persistent vegetative state; patients in persistent vegetative state have lost all cognitive neurological function but are still able to breathe and may exhibit various spontaneous movements. They may even be awake and appear to be normal but, because the cognitive part of their brain no longer functions, they are not able to respond to their environment. A vegetative state can last for years.

There are other terms, in addition to coma and vegetative state, that are used to describe varying levels of unconsciousness and a person's ability to respond to stimuli. These include stupor, in which a person is unconscious but will eventually respond to repeated, vigorous stimulation; and obtundation and lethargy, which are used to describe a person who is not entirely unconscious but does not respond to stimuli.

Usually, coma and other altered states of unconsciousness are considered neurological emergencies, and actions need to be taken quickly to avoid permanent damage.

The Human Brain
The human brain is made up of three basic parts: the cerebrum, the cerebellum, and the brainstem. The cerebrum is the largest part of the brain and makes up about 85% of the brain's total weight. It's divided into two hemispheres, the cerebral hemispheres, one on each side of the head. The cerebrum is where all of the body's most complicated mental and sensory functions are controlled—intelligence, reasoning, memory, emotions, vision, the ability to feel, etc.

The cerebellum is a smaller part of the brain that lies behind the cerebrum. It plays an essential role in coordination, posture and balance. The brainstem is the stemlike 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 being awake and alert.

Unconsciousness
As with most mental processes that occur in the brain, the biology of consciousness—also called arousal—is very complicated and not well understood. There are many tissues located deep within the brain that play a role in how conscious and alert a person is.

Researchers believe that one of the important physiological processes that keeps a person conscious is the transfer, or neurotransmission, of chemical signals from the brainstem to the cerebral hemispheres of the brain. This continuous neurotransmission needs to be happening in order for a person to be aware of their environment. Abnormalities that interrupt it can lead to coma or other states of unconsciousness.

Abnormalities that can cause coma include injury or damage to the brain that leads to swelling (edema) in the brain, which results in an increased intracranial pressure (pressure within the skull). Increased pressure, whether it is localized in one particular spot or spread over the whole brain, decreases the flow of blood and can lead to unconsciousness.

Injury or damage to the brain can also cause some areas of the brain to shift within the skull and exert pressure on surrounding tissues and structures, including blood vessels. When a part of the brain shifts position like this, the event is called a brain herniation, and it can lead to coma and death if not treated immediately.