The Brain and How Strokes Occur

Imagine, for a moment, you're going through your day and suddenly you have a pounding headache and, although you're in familiar surroundings, nothing looks familiar.

Suddenly, you're aware of a spreading warmth between your legs. You've wet your pants. You've also fallen to the floor. No matter how hard you struggle to get up, you can't. Neither your arm nor your leg will move. You try calling for help, but the words coming out of your mouth are gibberish. If you're alone, a frightening thought overwhelms you: What if no one finds me?

This scenario describes what it might be like if you suffer a stroke. A frightening proposition, indeed, especially in those first hours and days. You wonder if you will live. Will you be impaired? How long will rehabilitation take? How complete will recovery be? These are just a few of the questions that might race through your mind or the minds of loved ones.

Unfortunately, there are no standard answers to these questions. However, for most individuals, the ability to understand and adapt to this new reality depends largely on their attitudes and efforts as well as on support from family, friends, healthcare professionals, and caregivers.

In this chapter, we'll discuss the complexities of strokes and how they occur. In order to better understand how strokes affect the brain, let's first review the basics of how the brain works.

Brain Anatomy

The upper brain, or cerebrum, is divided into two hemispheres. The cerebrum contains the cortical area, used for thinking, and the subcortical area, a complex network of nerves that act as relay centers and linking pathways. Each hemisphere has four separate lobes: frontal, parietal, temporal, and occipital. Frontal lobes — located in the front of the brain — control thinking, behavioral functions, and body movement. Parietal lobes assist in sensation, concrete thinking (such as math), abstract thinking, vision-space orientation, and language. The temporal lobe is part of the emotional and memory center and also contains language functions. The occipital lobe is the part of the brain that interprets what we see.

The back part of the brain, the cerebellum, controls balance and coordination. Under the cerebrum lies the brain stem. It controls involuntary and automatic survival processes we don't need to think about, such as heart rate, body temperature, breathing, sleeping cycles, and the regulation of some hormones.

How Blood Flows to the Brain

Blood moves from the heart to the brain through the large carotid arteries, which travel up each side of the neck along the windpipe. Once inside the skull, the carotid arteries divide into front and side branches. These blood vessels supply the front two-thirds of the brain's outer surface. The vertebrobasilar arteries travel upwards and serve this region as well as the coordination centers and the brain stem.

How the Brain Sends Signals

The wiring of nerves in the brain is complex. Although the two hemispheres of the brain look identical, they handle separate functions. Each hemisphere controls movement and sensation on the opposite side of the body. For example, if you put your left hand under hot running water, the right cerebral cortex interprets the stimulus as pain. To reach forr an ice cream cone with your right hand, the left side of the brain generates a signal. The left part of the brain is dominant in right-handed people, while the right portion of the brain is dominant in left-handed individuals.

Stroke: "Brain Attack"

A stroke is a "brain attack" in the same way a blockage of blood flow to the heart is a "heart attack." A stroke occurs when an area of the brain is deprived of blood flow. Most commonly, this happens when blood vessels are blocked by a clot or have become too narrow for blood to pass through. A stroke may also occur when a blood vessel bursts and leaks blood into the brain, causing damage. A lack of blood pumped to the brain, the result of a heart attack, may also cause a stroke.

When blood flow to the brain stops suddenly, a person will fall unconscious in about twelve seconds. Since the brain relies on the glucose and oxygen carried by blood cells for energy, brain cells will begin to die after about four minutes without these nutrients. This is a critical situation. Unlike other body tissues that have the ability to repair themselves over time, brain tissue is highly specialized and is less able to recover.

If Someone Is Having a Stroke

Are you aware of the signs of a stroke? Do you know what action to take if you think a loved one or friend is having a stroke?

Symptoms include: numbness or weakness in the face or limbs, sudden confusion and trouble speaking, trouble seeing, sudden dizziness or loss of balance, and sudden headache. Getting emergency medical care quickly is critical. The majority of strokes (80 percent) occur as a result of blood clots in the brain. Individuals having this type of stroke are often candidates for a clot-busting drug called tPA, tissue plasminogen activator. The drug can significantly reduce brain damage and the resulting disability after a stroke. However, the drug must be given within three hours of the onset of symptoms. Therefore, it's also important to tell hospital personnel when the stroke patient's symptoms started.

Unfortunately, most people delay calling for help, according to a 2010 study completed by researchers at the Michigan Department of Community Health. The researchers reported that in a survey of 4,800 people, only a fraction said they would call 911 if they observed a relative or friend showing symptoms of stroke.

Remember also that you may be the person who needs to call 911. A stroke can injure a person's brain, and he or she may not be able to tell you of their symptoms. Therefore, the best thing you can do if you think someone is having a stroke is to call for an ambulance immediately. The difference can save a life and reduce the chance for permanent disability.

Those conducting the Michigan study also urge the public to call 911 for an ambulance rather than transport a stroke victim themselves to a hospital emergency room. Patients who are transported by ambulance can begin receiving treatment immediately upon the arrival of emergency medical personnel. Also, patients transported by ambulance reach hospitals sooner and receive treatment sooner than those who are taken to the hospital by relatives or friends.

Major Causes of Stroke

Thrombosis

The leading cause of stroke is thrombosis, or blood clots. Clots develop gradually when the inner lining of blood vessels become clogged with the build-up of cholesterol and fatty substances. This clogging is similar to the deposit of lime scale in water pipes: Eventually enough scale accumulates to narrow or totally shut off the flow of water. In blood vessels, a build-up of cholesterol from years of eating a high-fat diet may have the same effect. Progression toward a stroke may be either sudden or incremental. Symptoms and conditions may alternately worsen or improve over hours or weeks.

Embolism

The second major cause of stroke, embolism, occurs when a clot...