What is the difference between unconsciousness and coma?
The conscious state of mind results from good brain function called cortical activity and combination of active ascending reticular activating system (ARAS), which is responsible for keeping us awake. The ARAS gets inputs from all parts of body, as far as the sensory and motor functions of the body.
For example, what is the environment, whether it is day or night, where you are standing , walking, and doing some work, what is the position of your body, what you are seeing, what you are hearing, etc. This ARAS is composed of multiple brain cells, and nerve fibres interlaced like the web of the Internet, which receives, sends all the inputs to it. It is to be enforced, that ARAS is AWAKE even during sleep.
The other part of the story is that there should be a recipient of this ARAS output. It is called cerebral cortex. Unless the cortex is OK one cannot understand what this ARAS transmits. It is like a projector and screen phenomena. During unconscious state, there may be a transient loss of awareness, but response to painful stimuli, depending on the degree of loss of consciousness.
Sleep is a transient loss of consciousness. Hence the rule, the inflicted pain relieves unconsciousness may not be applicable in all cases.
But, in coma, the situation is different. There is a definite structural or functional defect in the ARAS, or cerebral cortex, where there is no response either at ARAS or at cerebral cortex. Unless these two systems are together, the interpretation of consciousness will not be entertained.
During simple unconscious state, the Electro Ecephalo gram (EEG), which is a test to detect the activities of the brain cerebral cortex, may be normal. But in coma, the EEG is abnormal, and suggestive of some abnormal brain activity like delta, and theta activities. Sometimes, a normal activity of the brain called alpha activity may be present throughout the brain area, which is abnormal, called alpha coma. Structural brain lesions, like head injury, injury to the brain stem, or metabolic situations like uremia, and diabetic keto acidosis, poisoning etc, lead to coma.
PROF Dr. V. NAGARAAJAN
Tamil Nadu Govt. Dr MGR Medical University
Madurai, Tamil Nadu