Someone has a stroke every 40 seconds in the United States, according to the U.S. Centers for Disease Control and Prevention (CDC).

A stroke, also called a “brain attack,” can cause brain damage, long-term disability and death. A stroke is always a medical emergency.

Strokes can occur at any age although it’s more commonly associated with adults, especially male adults. Nine in 10 of these persons are victims of an ischemic stroke. The others fall prey to a hemorrhagic stroke.

An ischemic stroke is triggered by a blood clot or plaque that blocks an artery in the brain. The sudden loss of blood circulation to an area of the brain results in a corresponding loss of neurologic function, hence the paralysis to one side of the body associated with this kind of stroke.

An ischemic stroke damages or kills brain cells within minutes, triggering symptoms in the parts of the body they control.

Many people with ischemic strokes are 60 years old or more, since the risk of stroke increases with age. Women are more likely to become victims of a stroke compared to men. This being the case, it would be wise to know exactly what an ischemic stroke physically does to the brain.

Our brains, especially its cells called neurons, depend on an immense network of arteries to bring it fresh blood from the heart and lungs. Human blood carries oxygen and nutrients to the brain, while at the same time taking away carbon dioxide and cellular waste.

If an artery is blocked, neurons can’t produce enough energy and will eventually stop working. If the artery remains blocked for more than a few minutes, the neurons may die. This is why immediate medical treatment is critical in an ischemic stroke.

Several kinds of diseases cause an ischemic stroke. The most common problem is narrowing of the arteries in the neck or head.

This condition is most often caused by atherosclerosis where cholesterol deposits gradually narrow the arteries. When an artery becomes too narrow, blood cells can congeal and form blood clots. When sufficiently large, these blood clots can block the artery where they are formed (thrombosis). They can also dislodge and become lodged in arteries closer to the brain (embolism).

Blood clots in the heart are another cause of stroke. These blood clots can occur as a result of irregular heartbeat, a heart attack or abnormalities in the heart valves, among others.

In contrast, the rarer but far deadlier stroke, the hemorrhagic stroke is caused by a diseased blood vessel that bursts and bleeds into the brain. The resulting intracranial hemorrhage is a serious medical emergency. The buildup of blood within the skull can lead to increases in intracranial pressure, which can crush delicate brain tissue or limit its blood supply.

If the amount of blood rapidly increases, the sudden rise in pressure can lead to unconsciousness or death. A hemorrhagic stroke usually occurs in selected parts of the brain such as the basal ganglia, cerebellum, brain stem or cortex.

Doctors say the most common cause of hemorrhagic stroke is high blood pressure or hypertension. High blood pressure by itself often causes no symptoms and this means many people with an intracranial hemorrhage aren’t aware they have high blood pressure, or that it needs to be treated.

While accounting for only 10 percent of all strokes, hemorrhagic strokes are far deadlier and cause four in 10 deaths.