The brain is the seat of all the commands of the body. It is located in the cranial box formed by the bones of the skull, supported by the meninges and thus protected; this box is inextensible.
The brain includes several regions: the two cerebral hemispheres, the cerebellum, in relation to each other and to the organs or other parts of the body. The brainstem is under the cerebellum and communicates the brain with the spinal cord that is in the spine. In adulthood, the brain weighs about 1, 300 grams.
Neurons and nerves
All regions are interconnected by nerve cells called neurons and form an extremely complex network. Neurons have extensions, nerve fibers; they regroup to form the nerves.
The brain has billions of neurons at birth and they gradually die as they get older. Until recently, it was thought that neurons did not multiply. But even in old age, it has been found that in a certain region of the brain, new neurons appear.
The nerve fibers allow to pass information throughout the body in the form of an electric current, the nerve impulse.
On the one hand, there are motor nerve fibers in which nerve impulses move from the brain towards the muscles, for example to control movement, and on the other hand, sensory fibers that transmit information to the brain.
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