Understanding Traumatic Brain Injury (TBI)
Scientists, doctors, attorneys, poets, and artists describe the brain in many ways. This organ controls thinking, sight, taste, touch, sound, and smell. It is also the area of our body that controls judgment, emotions, and the ability to distinguish between pleasant and unpleasant. Additionally, the brain controls motor functions (muscles), sleep, and our autonomic functions, such as heart rate. The brain has the make-up or texture of a sponge or gelatin. Some doctors referred to the brain’s texture as Jello-like. It weighs about three pounds. The brain has many important parts, which we will briefly discuss:
- Cerebral Cortex (also called the Cerebrum);
- Brain Stem;
- Membranes and Cerebrospinal Fluid;
The Cerebral Cortex, Cerebellum, and the Brain Stem comprise approximately 4/5 of the contents of the skull, with the remaining 1/5 consisting of Membranes and Cerebrospinal fluids. Although the skull is not technically a part of the brain, it is an important structure to understand. While its role is to protect the brain from outside forces, it can also contribute to brain tissue damage because of sharp ridges on the inside. According to one study, about 40% of those hospitalized with a TBI had at least one unmet need for services one year after their injury. The most frequent unmet needs were:
- Improving memory and problem solving;
- Managing stress and emotional upsets;
- Controlling one’s temper; and
- Improving one’s job skills.1
TBI can cause a wide range of functional changes affecting thinking, sensation, language, and/or emotions. It can also cause epilepsy and increase the risk for conditions such as Alzheimer’s disease, Parkinson’s disease, and other brain disorders that become more prevalent with age.2
- Corrigan JS, Whiteneck G, Mellick D. Perceived needs following traumatic brain injury. Journal of Head Trauma Rehabilitation 2004;19(3):205-16.
- National Institude of Neurological Disorders and Stroke. Traumatic brain injury: hope through research.
Cerebral Cortex or Cerebrum
The largest part of the brain is the cerebral cortex, also known as the Cerebrum. This structure is divided into two parts but connected by a bridge-like structure called the Corpus Callosum. These two hemispheres control speech, memory, and intelligence. The right hemisphere controls movement on the left side of the body and the left hemisphere controls movement on the right side. The Corpus Callosum carries nerve fibers from one side to the other, and therefore carries messages between the two cerebral hemispheres.
Lobes of the Cerebral Cortex
The two cerebral hemispheres are further divided into varies sections. There are four sections in the right hemisphere and four sections in the left hemisphere. These sections are called lobes. Each lobe plays a critical function, and all work together as an integrated system.
- The Frontal Lobe: Located just behind the skull of the forehead, the frontal lobe governs our ability to reason, make judgments, organize and integrate information, and control some motor/ muscle functions. It also holds the key to our personality and moods. It is easy to see why this lobe has come to be known as the area that manages our “executive functions.” An injury to this area can have a significant and negative effect on many activities in the life of a TBI survivor because it compromises the ability to organize time, projects and tasks. The location of the frontal lobe makes it more susceptible to injury in situations where one hits their head on a windshield, dashboard or steering wheel in a motor vehicle collision. Moreover, even in cases where the head does not hit a solid object, the frontal lobes may be injured by colliding with the bony ridges of the skull behind the eyes. Refer to chapter 3, “How the Brain Gets Injured” for more information on this.
- The Parietal Lobe: Located directly behind the frontal lobe, the parietal lobe provides and identifies sensory information, such as touch, heat, cold, and pressure, and distinguishes objects and sounds. It also provides naming, reading, writing, and mathematical problem solving functions. Another function of the parietal lobe is to help analyze visual information in 3-D space.
- The Temporal Lobe: The temporal lobe is located just above the ear and alongside both the frontal and parietal lobes. This part of the brain is related to hearing, smell, taste, and language comprehension. Recognition of tone, pitch, and music is also processed here. The temporal and frontal lobes focus on short-term memory and processing new information. These lobes are the most frequently injured lobes of the brain.
- The Occipital Lobe: Located at the back of the skull, the occipital lobe is involved primarily with vision. This lobe gives and receives impulses to interpret objects and store information related to vision. Injuries to the occipital lobe can impact a person’s ability to interpret spatial relationships, color perception and other aspects of vision.
Towards the back of the Cerebral Cortex and beneath the Occipital Lobes lies the Cerebellum. The Cerebellum has two hemispheres just like the Cerebral Cortex with a mid-line bridge connecting both hemispheres. The Cerebellum coordinates many functions involving balance, posture and equilibrium. The Cerebellum also regulates many automatic responses such as voluntary muscle movement. It operates “blueprints” of previously learned complex motor tasks, such as playing a musical instrument or doing a gymnastics routine.
The Brain Stem
Another major part of the brain, the Brain Stem, is located beneath the Cerebral Cortex but in front of the Cerebellum. Just as it sounds, this structure connects the brain to the spinal cord. It is through the brain stem that messages and nerve impulses going from the brain to the rest of the body must travel. Most of the important functions of the body are centered in the Brain Stem, including respiration, blood pressure, circulation, and helps regulate sleep cycles. Additionally, 12 cranial nerves begin in the Brain Stem and are responsible for activity such as smell, swallowing, hearing, vision, eye movement, facial sensation, taste and muscle movements in the face, neck, shoulders, and tongue.
Membranes and Cerebrospinal Fluid
As mentioned above, 4/5 of the skull is made up of the Cerebral Cortex, Cerebellum and the Brain Stem. However, there is another 1/5 of the brain consisting of membranes and cerebrospinal fluid which plays a vital and critical role in all brain activity. There are three layers of membranes covering the brain, called the Dura, Arachnoid, and Pia Membranes. Membranes are also known as Meninges. These membranes appear thin and clear and have a role of supporting and protecting the brain as well as assisting and separating its different parts. An injury to the membrane may be very important in certain types of TBI.
- Dura Mater Membrane: The outermost membrane just inside the skull is known as the Dura Mater or Dura. Very small blood vessels carrying nutrients to the brain travel through the Dura Mater. The veins in this blood supply have very thin walls. If the Dura is somehow disturbed during trauma, blood may escape into the space between the Dura and the skull and rapidly enlarge and form a clot. These clots are named by their location, such as an epidural or subdural hematoma. An epidural hematoma refers to a blood clot that is located outside the Dura. A subdural hematoma means the blood clot is located below the Dura. Blood clots of these types are very dangerous because they may distort and displace underlying brain tissue, compressing brain cells and the connecting tissues, and reduce blood flow. Because the brain is located in a closed space (the skull), a large blood clot that develops from bleeding blood vessels is a medical emergency since there is no room to allow for expansion or swelling following traumatic brain injury. Depending upon their size and location, hematomas and blood clots have to be removed surgically.
- Arachnoid Membrane: The second or the middle membrane is known as the Arachnoid Membrane. This middle membrane does not let any liquid pass through it. This allows for an uniform distribution of this fluid throughout the brain.
- Pia Membrane: The arachnoid membrane is separated from the third membrane, the pia membrane, by the subarachnoid space. This is where cerebrospinal fluid flows. Following traumatic brain injury, bleeding is possible in the subarachnoid space and may create a medical emergency.
- Cerebrospinal Fluid: Cerbrospinal fluid is a clear liquid ad serves to buffer the three membeanes frm each other but also the brain itself. The cerebrospinal fluid is critical because it carries nutrients between blood vessels and brain cells.
A few words are needed about the skull. The skull protects the brain from outside infections and bumps of daily life. The skull feels smooth on the outside when you run your hand over your head or across your forehead. However, as you can see from the illustration on this page, it is a very different story on the inside. The skull’s interior surface is not smooth. It is marked by sharp edges located very close to nerves, tissue, and blood vessels. When a brain collides with and rides over these bony structures during trauma, it is easy to see how it gets injured.
How the Brain Gets Injured
The brain can be injured in a variety of ways. We will look at 3 ways in particular:
- skull fracture or skull penetration;
- acceleration-deceleration injuries; and
- coup/contre-coup injuries.
- Skull Fracture: Let’s start with a basic understanding of the skull and traumatic brain injury. Brain injury can occur when the skull is fractured, resulting in brain swelling, brain contusion, or the entry point of bacteria and infection. Brain injury can also occur without a skull fracture, such as “shaken baby syndrome.” The skull is a very strong structure with rigid bones on its inside. It takes significant force to break or crack the skull. The brain, on the other hand, is a very soft gelatin-like tissue structure much like jello. A force that passes through the skull and penetrates the brain may cause severe injury. The skull is thinnest, and therefore the weakest, at the temporal lobe which is near the ear. As a result, many skull fractures occur in the area of the temporal lobe.
- Acceleration-Deceleration Injuries: The key to understanding the role of acceleration-deceleration forces in causing traumatic brain injury is to discuss “inertia.” This means that an object remains stationary or continues moving until acted upon by some outside force. In traumatic brain injury, the brain has inertia. For example, when a person falls backwards onto a hard floor, the back of the person’s head hits the floor and stops. The brain, however, is still moving until it strikes the inside of the skull. If the brain gets bruised, there is bleeding, also called a hemorrhage. This bleeding causes further damage to the brain. The skull does not need to strike an object in order for the brain to get injured. There are many situations in motor vehicle crashes where the forces are transmitted through the brain without the skull hitting the dashboard, windshield, steering wheel or window. Let’s look at acceleration-deceleration injuries in a rear-end motor vehicle collision. When a car is rear-ended there is a certain amount of force that is transmitted through the car. As a result, the occupants of the car begin to move forward. The brain which is inside the skull floats in a bath of cerebral spinal fluid and remains stationary by the membranes of the brain that attach to the skull. When the neck reaches the end point of moving forward, there may be rapid deceleration of the head, while the brain continues forward hitting into the interior structure of the skull. Contusions of the brain are usually more severe in parts of the brain closest to the skull, including the tips of the frontal and temporal lobes. The undersurface of these lobes are quite vulnerable because they are located next to the skull structures that are rough and irregular.
- Coup/Contre-Coup Injuries: Related to acceleration-deceleration injuries are coup/contre-coup injuries. These happen with a severe impact or after a fall when the head is struck. After the brain hits the inside of the skull it might actual bounce back and strike the opposite side of the skull, potentially resulting in two separate injuries to the brain.
Types of Brain Injury
We now have a sense of how the brain gets injured. Let’s review what happens on a cellular level in traumatic brain injury.
- Contusion of the Brain: Contusion of the brain’s surface occurs when the brain strikes the bone within the skull. Contusions occur at the tips of the brain: frontal (front), temporal (side), and occipital (rear). Large contusions may be seen on CT scans or MRIs as large bruises. Areas of contusion that are visible will be surrounded by a zone of swelling, known as “edema.” If this swelling is great enough, it may cause changes in consciousness, and in severe cases, may be life threatening. However, contusions are often microscopic or pin-point hemorrhages and are too small to be seen on currently used CT or MRI imaging tests. There is hope that in the near future technological advances with CT and MRI tests will allow better visualization of these hemorrhages.
- The contre-coup injury to the brain occurs when the brain strikes the skull on the opposite side of impact. Once the skull has stopped moving the brain continues striking the front of the skull. Contre-coup injury to the brain.
- The coup injury to the brain occurs when the brain strikes the skull on the opposing side of impact.
- Diffuse Axonal Injury: We mentioned previously in thechapter 2, “Brain Anatomy”, that the whole brain is a gelatin-like structure. However, each part of the brain has a different consistency and density. For instance, gray matter, which are the nerve cells, and white matter, the long connecting “tails,” or axons of the nerves have different weight. With traumatic brain injury, the brain undergoes a rapid deformation. When the brain is rapidly moved, different parts move at different speeds. This can cause nerves to be stretched or torn within the brain. This type of injury is often known as a shearing (stretched and torn) injury or “diffuse axonal injury” since the nerve fibers are sheared at the margin of the gray and white matter. A diffuse axonal injury can occur without a skull fracture or brain contusion. This stretching of the axon can kill the cell and destroy its connection to other cells. Torn axons cannot be repaired. Diffuse axonal injuries are often very difficult to diagnose because CT scans and MRIs may not be able to detect the microscopic lesions that occur from these types of injuries. Unfortunately, diffuse axonal injuries may result in prolonged or permanent behavioral, cognitive and overall disability.
- Excitotoxicity Injuries: At the time of a traumatic brain injury, those cells or neurons that are damaged will release an excessive amount of chemicals that are used to transmit messages to the next neuron. These chemical messengers are called “neurotransmitters.” When neurons are damaged, they may release large amounts of chemicals that may damage the next neuron, such as Glutamate and Aspartate. These chemicals stimulate neighboring neurons causing a chain of events within the neuron leading to eventual death of those cells. This is known as an excitotoxic effect. These types of injuries may not be seen immediately but can develop over several days following the initial head trauma. This delayed chemical process may help to explain the delayed onset of symptoms experienced by some survivors of traumatic brain injury.
Facts About Concussion and Traumatic Brain Injury
The word “concussion” is frequently used to describe an event in which the head is struck or strikes something, such as when athletes talk about having their “bell rung.” However, as a result of increased understanding of brain injury, concussion is now taken more seriously by medical personnel, coaches, and athletic trainers. A concussion represents a mild traumatic brain injury. The American Academy of Neurology has developed a standardized assessment of concussion, encourages its use for measuring three grades of concussion (I, II, III) and suggests appropriate bench time before returning athletes to play. A person sustaining a Grade I concussion might appear confused with no loss of consciousness and have difficulty maintaining a coherent conversation. The symptoms should resolve within 15 minutes. A Grade II concussion may have very similar symptoms. However, they last beyond the 15 minute time frame. Any loss of consciousness would be a result in a Grade III concussion and a person should be seen by a physician at once.