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The brain

The brain allows us to perceive and interpret the outside world. Its significance in vital processes such as our heartbeat, breathing and nutrition makes it an organ that is essential to life.

The anatomy of a compartmentalised organ

The appearance of the brain, a greyish-pink mass that is wrinkled like a walnut, does not do justice to its remarkable capacities. The brain accounts for around 2% of a person’s body weight and is made up of billions of nerve cells called neurones. It is one part of the encephalon (along with the diencephalon, brain stem and cerebellum) and is made up of two hemispheres of approximately equal sizes. The surface of these hemispheres is almost entirely covered with folds, known as gyri, separated by superficial ridges. The brain is mainly made of a whitish material (white matter), while its surface is covered with a thin layer of greyish material (cerebral cortex or grey matter). This difference in colour is due to the fact that the cortex mainly contains the neurones’ cellular bodies, whereas the white matter consists of a mass of axons that connect the various cortical areas together. At the centre of the brain, four ventricles (large C-shaped cavities) communicate with each other. The cerebrospinal fluid (or cephalorachidian fluid) inside these ventricles and around the brain, acts as a cushion and protects the brain from trauma.

Essential to all vital functions

The cerebral cortex or mantle is at the top of the nervous system hierarchy. It enables human beings to be aware of themselves and of their feelings, to communicate, memorise, move and understand. This essential organ regulates all vital functions. It is divided into four lobes: the frontal lobe, the parietal lobe, the occipital lobe and the temporal lobe. These lobes are then divided into numerous regions (over 50 in total) named Brodmann areas. Some areas have been associated with specific functions, such as speech for example, while more complex functions, such as memory, seem to involve several areas. The brain receives information from the entire human body through the nerves (sensory pathway), integrates and analyses them, then responds by emitting new signals that travel back down through the nerves (motor pathway) towards the relevant body parts.

The brain, our senses and food

The digestive system supplies the nutrients required for the brain cells to function. The brain can, in turn, act on feelings of hunger and fullness in response to changes in the concentration of certain nutrients and hormones in the blood, such as sugar and insulin. The stomach, for example, can also send the brain a signal saying that it is filling up, causing the brain to trigger the feeling of satiety. Yet food does not only involve hunger and satiety, it is also the origin of feelings of taste and pleasure. Gustative messages from the tongue are transmitted to the brain and analysed in the gustative area of the cortex. The brain can then recognise the various flavours of food, as each foodstuff stimulates a sub-group of neurones in this gustative area. Other events are also triggered in the brain, such as reflexes connected with digestion or the production of saliva or gastric juices.