In our relationship with the world, we are stimulated all the time and respond to the elements of the environment. At each external stimulus (such as the smell of food or the sound of a horn) and even internal stimulus (such as pain or hunger), the organism reacts, that is, in a way “answers these questions:
Where does the stimulus come from?
How does my body react to this stimulus?
Will it do me good or bad?
Have I had this feeling before?
This process occurs in the central nervous system so instantaneously that our consciousness cannot identify all its stages, nor the thousands of stimuli the body receives at all times.
To better understand how we perceive external stimuli and how we respond to them, it is critical to recognize the system that forms the body's communication network.
Why do we need a nervous system?
Your brain is the most important organ in your body. It controls everything you do, your movements, your thoughts and your memory. It often does not act directly, but can control small amounts of blood chemicals, which in turn have a strong effect on another part of the body.
Although it sounds very simple, the brain is immensely complicated. It is a mass of whitish tissue, quite soft to the touch, which occupies about half the volume of the head. It is positioned at the top of the head, above the eyes and ears, extending back and to the bottom of the head.
Almost as important as the brain is the rest of the nervous system. The spinal cord extends from the brain downward along the spine. The brain and spinal cord form the central nervous system.
Along the length of the spinal cord come out nerves similar to wires that split and connect with almost every part of the body. Nerves carry messages from the sense organs to the brain, as well as instructions from the brain to other parts of the body. The brain functions as a complicated but very compact telephone network, with a complex flow of incoming messages selected and then directed to its appropriate destination.
Because it is such an important organ, the brain needs good accident protection. By standing, the human being keeps the brain and head away from shocks and beats. Even so, very reliable protection is required. That's why the brain is housed in the skull, a hard bony box.
Although thin-walled, the skull is very sturdy due to its rounded shape. One of the strongest forms known is a rigid ball. An egg, for example, is extremely tough considering how thin its shell is. Thus, the soft and delicate brain is protected from direct external damage by the sturdy skull. However, even though the skull is rigid and strong, a violent shake could shake the brain and cause damage. More protection is then required, which is given by three membranes, called meninges, which completely cover the brain. The outermost membrane is called the Dura mater, which provides good protection and support due to its strong and leathery constitution.
Next to the brain is another membrane called sink, much thinner, which accompanies every depression and every elevation of the brain surface. Between these two membranes there is a third, spongy constitution, the arachnoid. The spaces in this membrane are filled with a liquid in which the entire brain floats, providing the final protective layer. There are still large spaces within the brain that are also filled with the same arachnoid fluid, so the delicate brain tissue does not deform when we move our head.