The middle cerebral artery is one of the three major arteries that supply blood to the cerebral cortex. It supplies portions of the frontal, parietal and temporal lobes, as well as some deeper structures beneath the cortex. A stroke can affect the entire area of its blood distribution, or can block only one of its branches, leading to a lesser degree of damage. According to the Internet Stroke Center of Washington University, the middle cerebral artery is the artery most often involved in strokes.
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The motor area, which controls all the muscles in the body, is located in the posterior portion of the frontal cortex. Representation of the body is in order; in other words, the nerves controlling the face are next to those controlling the neck, and so on. According to "Adam's and Victor's Principles of Neurology," complete occlusion, or blockage, of the middle cerebral artery leads to paralysis of the entire opposite side of the face and body. Partial occlusion can affect only some areas, leading, for example, to paralysis of one arm, or to paralysis of the arm and leg, while sparing the face. Paralysis may improve over time and the patient can regain some of the functions lost due to the stroke.
The body's sensory input travels to a strip located in the anterior portion of the temporal lobe, paralleling the motor strip which is located in front of it. Strokes in the middle cerebral artery can lead to loss of all sensation in the other side of the body, or to loss of sensation only in some areas, such as the face, neck and arm.
The visual signals from the eyes pass through the temporal lobe on their way to the part of the cortex responsible for vision. Strokes of the middle cerebral artery can cause loss of half of the visual field in both eyes, on the opposite side to the stroke. The defect might be partial--for example, the patient might lose vision in quarter of the visual field. Another visual symptom is difficulty with gaze, that is, with moving the eyes together to the direction the patient wants to look at.
The left hemisphere is dominant in most people, containing the control centers for language. A stroke affecting the left hemisphere can cause several different symptoms. Some patients have halting speech. Others can speak fluently, but their speech is meaningless. Both comprehension and production of language can be affected. These deficits can be extremely disabling, but can improve over time.