Lobes of the Brain
The three main components of the brain—the cerebrum, the cerebellum, and the brainstem—have distinct functions. The cerebrum is the largest and most developmentally advanced part of the human brain. It is responsible for several higher functions, including higher intellectual function, speech, emotion, integration of sensory stimuli of all types, initiation of the final common pathways for movement, and fine control of movement.
The cerebellum, the second largest area, is responsible for maintaining balance and further control of movement and coordination.
The brain stem is the final pathway between cerebral structures and the spinal cord. It is responsible for a variety of automatic functions, such as control of respiration, heart rate, and blood pressure, wakefullness, arousal and attention.
The cerebrum is divided into a right and a left hemisphere and is composed of pairs of frontal, parietal, temporal, and occipital lobes.
The left hemisphere controls the majority of functions on the right side of the body, while the right hemisphere controls most of functions on the left side of the body The crossing of nerve fibers takes place in the brain stem. Thus, injury to the left cerebral hemisphere produces sensory and motor deficits on the right side, and vice versa.
One hemisphere has a slightly more developed, or dominant, area in which written and spoken language is organized. Over 95% of right handed people and even the majority of left handed people have dominance for speech and language in the left hemisphere [Mohr JP, et al: In: Barnett HJM, et al (eds). Stroke. Pathophysiology, Diagnosis, and Management. New York, Churchill Livingstone, 1992:331] Thus, a left hemisphere stroke will be more likely to produce aphasia and other language deficits.
Layers of the Cerebrum – Gray and White Matter
The entire cerebrum is composed of two layers. The 20-millimeter thick outermost layer, called the cerebral cortex (or gray matter), contains the centers of cognition and personality and the coordination of complicated movements. As shall be seen, the gray matter is also organized for different functions.
The white matter is a network of fibers that enables regions of the brain to communicate with each other.
Cerebellum and Brainstem
A stroke involving the cerebellum may result in a lack of coordination, clumsiness, shaking, or other muscular difficulties. These are important to diagnose early, since swelling may cause brainstem compression or hydrocephalus.
Strokes in the brainstem are usually due to basilar occlusion, although in many cases the clinical syndrome may fit the criteria for a lacunar stroke [Mohr JP and Sacco RL, 1992]. Brainstem strokes can be serious or even fatal. People who survive may be left with severe impairments or remain in a vegetative state.
Acute Ischemic Stroke: New Concepts of Care
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