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Overview of Stroke

During a stroke, blood flow into the brain is interrupted, causing a rapid loss of brain functions. All the parts of the brain rely upon constant blood flow to bring oxygen to the tissues, so if there is any disruption or significant reduction of blood to the brain, a stroke can occur. The severity of the stroke depends on the type of stroke, where within the brain the stroke occurs, and how long that part of the brain has gone without blood and oxygen.

There are two main categories of strokes, ischemic and hemorrhagic. The majority of strokes are ischemic, in which the loss of blood flow to the brain is caused by an obstruction in the vascular system that blocks the blood supply. In hemorrhagic strokes, the blood supply to the brain has been dramatically reduced due to severe internal bleeding. Hemorrhagic strokes may occur if a blood vessel ruptures, for example. Sometimes, hemorrhagic strokes also develop in areas where there is ischemia. As the blood pressure builds behind the blockage in a blood vessel, for example, it may rupture the vessel and cause significant leakage of blood into the body. This means that the blood has essentially escaped from circulation and can no longer travel to the brain or other tissues.

The brain is a very complicated organ and much about how it works is still not well understood, however, scientists have identified general structures in the brain that contribute to different categories of function. For example, in the front of the brain, just behind the forehead, lies the cerebral cortex. The cerebral cortex mediates consciousness, defining how we perceive and respond to our environments, and controls language, thought, memory, and attention. Opposite of the cerebral cortex is the occipital lobe, which processes visual information. In the top of the brain, between the cerebral cortex and occipital lobe is another sensory processing center called the parietal lobe. This part of the brain helps mediate coordinated movements of the body in response to what the eye sees, allowing for basic levels of hand-eye coordination. The temporal lobes above the ears are critical for processing sounds, as well as some visual information. The temporal lobes also seem to be involved in speech, acquiring memories, and organizing information. In the lower part of the brain lies the cerebellum, which is crucial for processing input from all of the senses and helping to coordinate motor control. The brain is connected to the spinal cord via the brain stem, which helps manage a number of fundamental physiological processes, including regulation of heart rate, body temperature, blood pressure, digestion, breathing, and swallowing reflexes.

The brain is the center of the nervous system, where all information gathered by our five senses is integrated and interpreted. It helps us properly respond through thought, speech, movement, and reflexes. It regulates every aspect of our physiology, keeping our hearts beating and lungs breathing. Clearly loss of any aspect of these functions can be devastating and a stroke can cause brain tissue damage such that the function is permanently lost. A stroke is a very serious and potentially life-threatening emergency.

Symptoms of Stroke

People at risk for strokes sometimes have smaller, mini-strokes that are caused by brief interruptions in blood supply to the brain. These are termed transient ischemic attacks (TIAs) and are normally caused by blockage of a blood vessel by a blood clot or other debris in the vascular system. Because these blockages are momentary, the symptoms are temporary and they usually do not cause permanent damage. The symptoms may include a sudden numbness on one side of the body, often an arm, leg, or side of the face. During a TIA, a person may develop a severe headache, have difficulty seeing out of one or both eyes, and may experience a loss of coordinate or balance that prevents them from walking. Depending on where the ischemia has occurred, TIA can also make a person feel confused and have difficulty speaking or understanding what others are saying. The symptoms of TIA normally last on average of a minute and no more than five minutes. Although the symptoms pass, medical attention should still be sought following a TIA because more than a third of patients that experience them go on to have strokes. Because of this, TIAs are also sometimes called "warning strokes," and treatment following a TIA can potentially prevent stroke and permanent brain damage.

Because the durations of the symptoms are very short, there is no permanent injury to the brain. This is the major difference between a TIA and a stroke. During a stroke, the symptoms are not only sudden, they last more than five minutes. The symptoms of stroke can easily be remembered by the acronym FAST, which stands for:

  • Facial weakness. Is there notable drooping of one side of the face, particularly in the eyes or mouth? Does the person have difficulty smiling? Is there numbness in the face?
  • Arm weakness. Is the person unable to lift both arms? Is there numbness in the arms?
  • Speech difficulty. Is the person unable to understand what you say? Is the person's speech slurred or unintelligible?
  • Time. If the answer is yes to any of the above three sets of questions, then an ambulance should be called immediately.

Because the symptoms of stroke depend on where within the brain the stroke occurred, not all of the symptoms may be present. If any of the symptoms described above are experienced, medical attention to be sought immediately, as any delay can put the person at risk for permanent damage to the brain.

Risk Factors of Stroke

The main risk of stroke is permanent damage to the brain. The symptoms are caused by blood and oxygen starvation of a particular part of the brain that is rapidly losing function, and if blood flow cannot be restored, loss of function will be permanent. Depending on the severity of the stroke, survivors of stroke may continue to deal with the impact of their stroke for the rest of their lives. If permanent damage occurred to their brain, they may have new physical, mental, or emotional disabilities. Some of the symptoms of the stroke itself may persist, including paralysis of the face and limbs. This may be as mild as feelings of weakness that may day to day activities difficult to accomplish or may affect their ability to walk. There may also be vision loss, chronic pain, and difficulties with speech. The ability to think clearly, make decisions, and solve problems may be permanently impaired. Should a stroke occur in a part of the brain that controls fundamental parts of our physiology, such as breathing and regulation of heartbeat, it may be permanently incapacitating or fatal.

Survivors of strokes are also at a risk for developing depression and sudden mood changes. These emotional issues may be partly due to the stresses and trauma surrounding having a stroke, but also because of changes to parts of the brain that help control mood and how we respond to the things that happen around us. Dementia can also result if the brain has lost the ability to interpret what the senses perceive.

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Article Last Updated: 08/26/2015