For those without medical training, trying to comprehend the intricate operations of the brain can seem overwhelming. Rest assured; it’s not necessary for a devoted caregiver to know how the brain works and what happens when it is injured, especially during the tense, confusing, and exhausting first few days or weeks after an injury. If you would rather not puzzle your way through the operations of the brain, feel free to skip this chapter. Doing so will not diminish your understanding of the rest of the book.
For readers seeking a basic knowledge of the brain, this chapter describes:
The Healthy Brain
The human brain is three pounds of a grooved, pinkish-gray, walnut-shaped, jelly-like substance. As vulnerable to sticks and stones as Jell-O, our most vital organ is guarded by four layers of defense.
The brain floats in a nourishing and cleansing pool of liquid called cerebrospinal fluid. Wrapped around the brain and bathed by this fluid are three sheet-like, shock-absorbing membranes or meninges, which extend down through the body with the spinal cord. Enclosing the brain and the meninges are the eight, quarter-inch-thick skull bones. These bones are covered by muscles, skin, hair, the occasional hat, and—not nearly often enough—a helmet.
The brain houses a complex network of billions of microscopic nerve cells called neurons. Each neuron, which is separated from its neighbors by an infinitesimal gap, has three parts. We need only be familiar with the long, wiry axon, which transmits signals to and from adjacent neurons.
When you wake up with a yawn, ponder the day ahead, smell the coffee brewing, stretch your muscles, and climb out of bed, signals speed from one neuron to the next, propelled by an electrical pulse that triggers the release of chemicals known as neurotransmitters. The possible pathways for nerve messages circulating at unfathomable speed around the brain are endless, some sixty trillion. They rearrange themselves constantly as we go about our daily activities.
Located at the base of the brain is a mass of thick nerve fibers called the brainstem. It connects the brain to the spinal cord, which passes messages between the body and the brain. The brainstem also houses the control centers of those activities that usually occur automatically, such as breathing, heartbeat, digestion, and, of particular note for our purposes, arousal or consciousness.
The brain is nourished by blood—which contains oxygen—through four arteries at its base. If one artery becomes blocked or damaged, the other three expand to maintain a sufficient flow of blood and oxygen. The brain is harmed by a lack of blood and oxygen much faster than any other body part. Without oxygen, neurons die.
Each component of the brain has its unique role. Matching the areas of the brain to their particular functions demands a degree of medical terminology and explanation beyond this elementary discussion.
Our more complex abilities, such as speech and memory, are performed by two or more components cooperating. For example, the brain has no single memory center. Our memories likely are stored as pathways among the billions of neurons.
After hours of reading about brain injury, I can’t match Jessica's deficits with the damaged portions of her brain. This is not to say that physicians are unable to predict likely impairments based on the location and gravity of an injury. What I’m suggesting is that caregivers without a medical degree be cautious in making their own prognoses.
The Injured Brain
Most brain injuries are caused by some form of trauma, such as a car collision, a bicycle accident, a gunshot wound, an assault, a sports mishap, a fall, or the concussive blast of an improvised explosive device on the battlefields of Iraq and Afghanistan. These are called traumatic brain injuries or TBIs.
There are two types of traumatic brain injury: (1) closed head and (2) open head. Sometimes, TBIs are accompanied by a brainstem injury and/or a coma. They also can be magnified, sometimes fatally, by secondary damage. A few other ways to describe a traumatic brain injury include diffuse axonal, acceleration/deceleration, coup contrecoup, and focal.
Finally, there are acquired brain injuries or ABIs, which cover those brain injuries that arise due to something other than trauma.
Let’s try to make some sense of this medical jargon, starting with the most common form of traumatic brain injury, closed head.
Closed Head Injuries
The majority of traumatic brain injuries are closed head. The skull is left intact and the trauma to the brain is not visible. Closed head injuries usually occur when some form of trauma causes the head to rapidly switch direction. This propels the brain ricocheting back and forth against the sharp interior knobs of the skull bones, traumatizing tissue.
Open Head Injuries
In an open head traumatic brain injury, an external force tears open the scalp, cracks the skull, rips apart the membranes, and pierces the brain.
Brainstem Injury
In a brainstem injury, the bundles of nerves that control the body’s automatic processes are twisted or torn as the brain caroms around the skull.
Secondary Damage
Recovery from a brain injury does not start immediately after the initial trauma. Secondary—sometimes even fatal—damage can occur hours, days, or weeks later. In fact, this secondary damage, if not addressed, can be more harmful than the initial blow.
Secondary damage occurs when the bleeding and swelling of injured brain tissue crowd into the finite space of the rigid skull. This elevates the patient’s intracranial pressure. As pressure rises within the skull, three life-threatening events can happen:
Other secondary dangers doctors watch for after a brain injury include:
Trauma physicians have a number of options to stabilize the patient and limit secondary brain damage. They can:
Diffuse Axonal Injury
An injury is labeled diffuse when multiple areas of the brain are involved. This typically occurs after a sudden acceleration or deceleration of the skull, as happens, for example, in a motor vehicle crash. When Jessica’s car was struck by the rapidly traveling SUV, her body was held in place by her seat belt, but her brain was launched like a basketball, rebounding off the inside of her skull many times.
With a diffuse axonal injury, a vast number of neurons are twisted, stretched, and/or compressed. Since the damage occurs on a microscopic level, the devastation—though considerable—may not appear on CT (computed tomography) scans, the doctor’s number one tool in detecting a brain injury.
Coup Contrecoup Injury
Another form of traumatic brain injury is the coup contrecoup injury, which causes a cerebral contusion or a bruise to the brain.
A coup injury occurs at the site of the brain that either slams into the skull when the head stops abruptly or absorbs the impact of an object, such as a brick wall or a baseball bat.
A contrecoup injury occurs when the force of the coup injury is strong enough to propel the brain to the opposite side of the skull. In this case, the brain is bruised in two areas.
Coup and contrecoup traumas are called focal injuries in which the harm is limited to one or two areas, as opposed to the widespread damage of an acceleration-deceleration diffuse axonal injury.
Acquired Brain Injury
Unlike traumatic brain injuries, which are triggered by an external force, acquired brain injuries result from some internal event, such as a stroke, heart attack, aneurysm, tumor, infection, disease, poisoning, or substance abuse that disrupts the normal operations of the brain’s neurons.
Acquired brain injuries also occur when there is an interruption in the supply of blood and oxygen flowing to the brain. Without oxygen, neurons begin to die after about four minutes.
At our elementary level of discussion, the consequences of a brain injury—traumatic or acquired—for the survivor are similar.
Note: Recently, the definition of acquired brain injury has been broadened by some to include all damage to the brain acquired after birth, including traumatic injuries. Obviously, this can cause some confusion when using and interpreting this term.
The Healing Brain
The medical world has developed ways to keep people with horrendous brain injuries alive, but it has not yet found ways to return these patients to their pre-injury condition. The human brain has an amazing ability to heal itself, but once neurons are dead, they are gone for good. Once the connections among neurons are severed, they cannot be reattached. This is why all survivors of a serious brain injury suffer some permanent impairment.
This does not mean that people living with a brain injury cannot improve their condition. Nearly all survivors—through hard work—are able to regain some capabilities lost to their injuries.
How are they able to do this?
For maximum benefit, survivors should begin formal rehabilitation as soon as they are responding to commands. This enables professionally guided therapy to work in sync with the natural healing of the brain.
Recovering from a serious brain injury is a mammoth undertaking. In the initial days of their recovery, survivors often are as helpless as an infant. The connections among billions of neurons in their brain have been severed. Messages cannot pass. The activities dependent on these messages—even a task as simple as getting out of bed—are unmanageable.
Jessica complained of an aching leg whenever she lay on her left side. She endured this pain because she couldn’t recall how to change her position in bed. For Jessica to once again be able to switch from her left side to her right side she had to relearn and practice this simple maneuver until she had mastered it.
Given that it takes a lifetime to accumulate the information stored in one’s brain, it’s not surprising that recovery can be a lifelong process. The brain is the slowest part of the human body to heal. The spontaneous recovery of damaged neurons takes months. The rewiring of the brain can take much longer.