The brain is the control centre for virtually every vital activity necessary for survival including movement, sleep, hunger and thirst. In addition, all human emotions including love, hate, anger, elation and sadness are controlled by the brain. It also receives and processes signals that are sent to it from other parts of the body and from sources external to the body.
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The brain comprises three distinct but connected parts; the cerebrum, the cerebellum and the brain stem.
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The largest part of the human brain is the cerebrum which makes up approximately 85% of the brain’s weight and has a large surface area called the cortex. It is an intricately developed part of the brain which accounts for the superior intelligence of humans, compared with other creatures. The cerebrum is divided by a fissure into identical right and left hemispheres.
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In turn each cerebral hemisphere is divided by fissures into five lobes. Four of these lobes are named from bones of the cranium; the frontal, parietal, temporal and occipital lobes. The fifth lobe, the insula, is located internally and is not visible at the outside of the brain.
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The cerebellum lies in the back part of the cranium beneath the cerebral hemispheres and is composed of two hemispheres connected by white fibres called the vermis. Three other bands of fibres (the cerebellar peduncles) connect the cerebellum to other parts of the brain.
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The cerebellum is essential to the control of movement of the human body and acts as a reflex centre for coordination and maintenance of equilibrium. It is this part of the brain which controls all activity, from manipulating a pair of knitting needles to a batsman smashing a ball to the boundary.
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The brain stem is all the structures lying between the cerebrum and the spinal cord and is divided into several components including the Thalamus, Hypothalamus, Midbrain, Medulla Oblongata, Pons, Limbic System and Cranial Nerves.
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These components regulate, or are involved in, many vital activities necessary for survival. The Hypothalmus, for example, is concerned with eating, drinking, temperature regulation, sleep, emotional behaviour and sexual activity, and within the Modulla are the vital control centres for cardiac and respiratory functions as well as other reflex activities, including vomiting.
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Oxygen and glucose are supplied to the brain by two sets of cranial arteries known as the Vascular System. Below the neck, each of the common carotid arteries divides into an external branch to supply the forward portion of the brain. The rest of the brain is supplied by the two vertebral arteries and these join together with the two internal carotid arteries to form the Circle of Willis at the base of the brain. Of all the blood pumped by the heart, 25% is circulated within the brain tissue by a large network of cerebral and cerebellar arteries.
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