How It Works and How It Is Injured

based on an article by Heidi Huddleston, R.N. in the 1996 BIAK Resource Journal

The brain is an extremely complex organ located at the top of the spinal column and resting upon the axis of the brain stem. Its firm gelatin-like consistency is cushioned by several layers of membrane (dura) and is cushioned in a fluid (cerebrospinal fluid) which allows it, in a sense, to float within a hard non-expandable shell of bone (skull).

The brain, which is made up of billions of interconnecting nerve cells (neurons), coordinates both the physical and mental activities of the body by receiving and interpreting messages and then responding to them. We are, thus, able to move, breathe, communicate, exhibit emotions and process information.

The Role of Various Parts of the Brain

The brain stem may be considered the most vital part of the brain since it is the area which is responsible for controlling the basic functions necessary for survival-breathing, heart rate and consciousness.

The cerebellum is the second largest part of the brain. It is, in essence, a relay station. It does not actually initiate any activity; rather it is responsible for the coordination or "smoothing out" of muscle activity.

The cortex is the largest and uppermost part of the brain. It is divided into two sides (hemispheres) each having its own primary functions. It is the left side, however, which is usually the dominant hemisphere. In most people, therefore, it is this side which controls speech, written language, reading, listening and calculating. The right hemisphere is primarily responsible for higher cognitive skills and functions such as rhythm, drawing, copying and visual memory. In left-handed individuals, however, this dominance may be either incomplete or completely reversed.

It is also helpful to understand what might be referred to as a "cross-over effect" in which the side of the brain responsible for motor or sensory function is usually opposite the affected side. For instance, use of the right side of the body is a left-sided brain function and the use of the left side of the body is a right-sided brain function.

As well as being divided into a right and left hemisphere, the cortex is divided into four sections (lobes), each having its own primary functions.

Located at the front of the brain, the frontal lobes have a role in behavior, social functioning, voluntary movement and expressive language.
Below and slightly behind the frontal lobes are the temporal lobes responsible for processing information, receptive language hearing and memory.
Above are the parietal lobes which play an important part in sensory functions and reading.
At the back of the brain are the occipital lobes which are primarily involved with vision.
Therefore, if you are told that there is damage to the frontal lobes, you might expect behavioral or expressive language problems whereas if there is damage to the temporal lobes, you might expect memory problems.

In a typical injury such as the type seen when a motor vehicle's forward motion stops suddenly, the initial injury often results from the steering wheel or windshield. The head subsequently may be thrown back towards the rear of the vehicle so that the brain may rebound from the site of impact and strike the inner surface of the opposite side of the skull (a coup/contre coup injury) resulting in yet further damage.

The size and weight of the brain resting on the thin spinal column makes it susceptible to twisting and turning on its axis, the brain stem. This can result in a loss of consciousness which, if it lasts for more than brief period of time, is called a coma.

Another result occurring when the brain is subjected to rapid deceleration is shearing. The inside of the skull is actually quite coarse. Tiny shock waves move through the brain tissue shearing and tearing nerve fibers and blood vessels often too small to be seen by the naked eye.

In addition to injury incurred at the time of the accident, further damage can follow as a result of several secondary effects. Bleeding inside the skull (hemorrhaging) can cause a mass of blood (hematoma) to accumulate. If this mass of blood is enough to put pressure on the brain tissue, additional damage may result. Bleeding can also interrupt or cut off blood flow to other parts of the brain (ischemia) resulting in a lack of oxygen to the areas (anoxia or hypoxia). Yet another cause of damage to the brain is swelling (edema). Because the brain is surrounded by the skull, there is no room for the brain to expand. Both bleeding and edema may increase intracranial pressure, so it is vitally important that it be closely monitored. Since injury to the brain most often involves injury by more than one mechanism and results in damage to multiple parts of the brain, it is referred to as diffuse damage.

Although there are many problems associated with traumatic head injury, some of the most common are: physical impairments such as paralysis, weakness (paresis) and contractures; cognitive difficulties such as loss or impairment of ability to use or comprehend words (aphasia) and difficulty in expressing oneself clearly (dysarthria); and behavioral problems. In order to assist you in making sense of some of the changes you may encounter after a brain injury, it is helpful to have a basic understanding of the physical functions of the brain.

Source: 2007 Resource Journal

Address information

Brain Injury Alliance of Kentucky 7321 New LaGrange Road, Suite 100 Louisville, Kentucky 40222