Nervous system, text 3. <small>The basic function, the interaction of the main parts.</small>

Thus, the sensory organs register changes that take place outside and inside our body. Information about the changes is transmitted in the form of "inward" / sensory/afferent nerve signals/nerve impulses/action potentials via the PNS into the CNS.

Once inside the CNS, the signals are spread to a large number of reception centers where, more or less unconsciously, they are analyzed, processed and compared with memories of past experiences and affect the emotional mood. The results of these, often "lightning fast", processes are used as a basis for planning the decisions that will govern the continued behavior.

Before the decisions are implemented, the likely outcome of the planned behavior change is calculated and evaluated. This "impact assessment", which can also be more or less unconscious, is extraordinarily important in terms of rational behavior, not least when it comes to our interaction with other people.

When decisions about the continued behavior have been made, "outward" motor/efferent signals are sent from the CNS, via the PNS, to the so-called effector cells or effector organs, i.e. to muscle cells and glandular cells, usually it takes less than a second from when the nervous system receives a sensory stimulus until the decision on the continued behavior is executed.

At the same time, there is a constant and unconscious check that the behavioral programs are really carried out in the way that the brain decided, e.g. that a certain movement is carried out according to the plan. Control is exercised through feedback "feed back". The brain is notified that a movement is carried out correctly from a number of different sensory organs inserted into the muscles and skin. In the musculature are the spindles that tell the brain how long our muscles are, and how their length changes and how fast the change is. In the tendons of the muscles are located the tendon poles that measure the force of a muscle contraction. In the skin around joints, in the sole of the foot and palm of the hand there are strain gauges that register how the skin is stretched during different movements. With the help of this information, the brain can then determine whether the program has gone according to plan or not. In the latter case, the error is promptly corrected. The control functions are very fast and take less than 1/2 second.

Simple well-rehearsed behaviors that respond to changes in a familiar environment can be triggered very quickly in less than a 1/4 second, being more or less reflexive and without "impact analysis". More complex behaviours, and especially those which have to come into force with a certain time delay and then in a series of different stages, obviously require longer preparation time.