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Biology 202, Spring 2005
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Why Are Humans Vulnerable to TBI (Traumatic Brain Injury)? And How Do We Really Define Brain Death?

Jasmine Shafagh

After a recent family member's loss due to what doctors call brain death, I started to question whether or not the brain is truly safe. After billions of years of evolution, one would think that humans have evolved into a present, ideal state of being. With current technological innovations, doctors are also more capable of curing and treating patients for sustained and prolonged life. However, despite the extensive medical attention which can be provided for patients, there is always a limit to our own bodies' capacities and threshold for maintaining life. As I mentioned above, my uncle recently passed away due to a traumatic fall from a flight of stairs. The traumatic brain injury (TBI) that he suffered caused his brain stem to cease functioning, and this, in turn, made him brain dead. Before this incident occurred, I never truly understood the fragility that comes with life and living in our own bodies. As I said before, doctors can only do so much to sustain our lives when injuries occur. But how come our own bodies, specifically our brains, have been created to be so susceptible to traumatic brain injuries in the first place? And how can one truly define brain death as opposed to the "body's death"?

According to a source, "The brain is the hub of the central nervous system and controls all bodily functions and processes," (4). More important than the actual brain is the brain stem, which is at the base of the brain and continually carries signals from and to the body. By sending these signals, the brain stem controls our consciousness, fatigue levels, heart rate and blood pressure. Thus, if the brain stem ceases to function, due to bleeding, swelling, bruising and tearing of brain tissue (from a traumatic brain injury), an individual can enter a state of coma (unconsciousness) because he or she can no longer control the body. Coma is defined as "damage to the brain's thinking and life support centers," (5). Thus, the brain stem can be considered as the body's life support center because it does control consciousness, our heart rate and blood pressure! (5).

So now that we understand why an individual can get brainstem damage and enter comas, we should know how these damages occur in the first place. "Traumatic brain injury (TBI) is sudden physical damage to the brain," (2), which is the leading cause of death for persons under the age of 45 in the United States. TBI occurs most commonly due to motor vehicle accidents, falls, or sports injuries! (3). Because of the high number of fatalities due to TBI, there is no doubt that our brains are extremely susceptible to both penetrating head injuries and closed head injuries, (or that people are engaging in more risky behavior these days.) Penetrating injuries are caused by damage occurring along the route that a particular object has taken into or through the brain. Closed injuries occur when there is a certain blow or pressure against the head, damaging the interior of the brain (1). Both can cause either primary damage (fractures, hematoma, and lacerations) or secondary brain damage (edema, epilepsy, increased intracranial pressure) (1).

While the dangers associated with penetrating injuries are obvious (such as a gunshot wound), many people do not understand the severity of closed-head injuries. They are not aware that the brain continues to move after the skull hits a stationary object and becomes still. The brain's continued movement inside the skull causes bruising, bleeding, or damaged nerves on the inside of the skull, all of which lead to more severe problems like increased intracranial pressure, hemorrhaging, and brain stem dysfunction (2). In the most severe TBI cases, the abundant brain swelling and intracranial blood pressure put an enormous amount of added pressure on the brainstem (the part of the brain that controls consciousness), causing the brainstem to cease functioning and the individual to become brain dead and fall into a permanent coma, (as explained above) (2).

Then why, might we ask, is the human brain so susceptible to TBI and other brain injuries? First of all, we must always remember that "While the brain is by far the most complex object on earth, it is soft and vulnerable with a consistency of firm pudding," (3). The human brain, because it is so soft, can be vulnerable to TBI in many ways. First of all, the cerebral cortex can easily be bruised when the head or brain comes in contact with hard objects. Secondly, the gray matter can also easily suffer from diffuse axonal injury. (Because the brain has nerve cells in the grey matter that send signals through their axons to the white matter, sudden impact to the brain causes the axons of the nerves to twist or become damaged so they can no longer transport the necessary signals) (3).

Thirdly, some of the resulting types of brain injury are: Edema (swelling, which increases the intracranial pressure and prevents oxygenated blood from entering the brain,) Hematoma (Blood clot formed by tissue injuries,) or Hydrocephalus (when blood gets into the cerebrospinal fluid and inhibits fluid "absorption sites," enlarging the ventricles and adding extra pressure in the brain (3).

Ultimately, once these irreversible damages occur to the brain stem, individuals are considered brain dead. Because the brain stem controls breathing, blood pressure, heart rate, and consciousness by sending signals to the rest of the body, damaged brain stems can no longer send signals to the rest of the body to make it function. Brain stem death, in general, can be caused by: TBI, brain hemorrhaging, thrombosis of blood vessels, cerebral anoxia, or brain tumors (7).

However, although brain stem dysfunction is a necessary condition for determining brain death, how can one truly distinguish death between one's body, and one's brain? While doctors today can maintain the functioning of our vital organs such as our heart and lungs for long periods after the brain has ceased working, ultimately, without those mechanical supports, the body itself would give out. The individual has reached a point where the "life-maintaining centers of the brain stem tissue" have stopped working, giving him/her a dead brain but viable body (if sustained through medical equipment) (6). In other words, once the dead brain cells cease functioning and regenerating, the brain can no longer control the body, and the body, without medical help, will eventually give out (7). But how long can one really sustain a body through hospital machines and ventilators? And when is it time to let go? To make these questions easier to answer and handle, laws have been passed, stating that once brain death has occurred, the individual being cared for is legally dead.
So how do you actually check for brain death? To do this, doctors must make sure that the following symptoms exist in patients: no electrical activity in the brain, no blood flowing into the brain, and the absence of the functioning of the brain stem (7). Doctors check if these symptoms exist by checking if: the patient's pupils don't respond to light, the patient doesn't breathe on their own, natural eye movements do not exist, the patient has no gag reflex, the patient doesn't respond to pain, or if the patient's eyes do not move when cold water is poured into the ears (8). In other words, brain death is "the irreversible loss of all function of the brain," (7).

However, even if an individual is brain dead, how come hospitals can not keep patients on life support? Why is it that the end of brain function creates death, even if the body continues to work on machines? Don't our bodies continue functioning with medications if we have severe medical problems? Then why can't the machines be considered "medications" that sustain life? The reason for this phenomenon is the human's extraordinary reasoning capacities. Lawmakers and doctors have come together to distinguish brain death as actual death due to the reasoning that if the brain doesn't work, the rest of the body can not work on its own. This point makes sense if we consider that "behavior can be operationally defined as the net sum of muscle and gland activity both of which constitute the output of neural function," (9). Thus, from a neurobiological perspective, if the neural function (brain stem function) ceases, our behavior ceases to exist, and thus, we become brain dead. This is in accordance with current laws used to distinguish brain death. At that stage in life, humans are only carrying out the life processes (i.e. "behaving") with the help of machines. Because the brain stem can't function, individuals can no longer control their own actions. As a result, they eventually become brain dead.

In sum, it seems as if the human brain is truly not a safe place because it is so vulnerable to traumatic brain injuries. Also, because the human brain is such a complex region, any small laceration or contusion can create devastating and long-lasting damage. With regards to the controversial issue of brain damage, I now have a better understanding as to how one can determine brain death and distinguish it from the body's death. In connection with our course material, I have truly come to understand that the brain does equal our behavior. As with brain damage and death, if the brain does not work, our behavior ends and we are considered dead. Thus, brain activity determines our behavior! From my research and new understanding of this topic, I advise people today to be extra cautious with their daily activities and to truly comprehend the fragility of the human brain and life.


1) American Speech-Language Hearing Association , has good information about traumatic brain injury.

2) National Institute on Deafness and Other Communication Disorders , has good information about classification of brain injuries.

3) Brain Injury Information and Medical/Legal Advice , has information about different types of brain injuries and on legal information about brain death and injury.

4) Online Neurology Channel , an overview of TBI information.

5) Brain injury Resources Center , has good information about comas and brain death.

6) Neurology and Brain Death , explains brain death.

7) What Is Brain Death? , explains brain death in detail.

8) Institute of Child Health, Brain Stem Death , explains brain stem death.

9) Klemm W. R., and Robert P. Vertes, eds. Brainstem Mechanisms of Behavior. New York: Wiley-Interscience, 1990.

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