1.c.7 – Perception and response: an important sequence?

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December 30, 2009 — Riccardo Sabellotti - Giacinto Sabellotti

percezione

Perception and response: an important sequence?

Even living in the same environment, we can find in very different situations: shifting from day to night and vice versa;  from warm to cold, from drought to rain; from insulation to the company, and predators can become preys. The life depends on these environmental changes and all the bodies, in some way, react to these stimuli. For reaction is therefore meant the creation of a change and this change may be physiological, as the reaction of the immune system in the presence of an infection, or behavioral, as a quick flight in presence of a predator. When a stimulus of the outside world leads to a consequent reaction, one can say that the stimulus was perceived; i.e. a signal that triggered a response was somehow received.
Considering the obvious and vital importance of this process, it is immediately understood how, during evolution, a myriad of systems for perceiving any sort of stimuli and to respond to them with a speedy reaction, has developed.
The unicellular beings are already able to respond to a wide variety of chemical and physical stimuli: for example, when they are in contact with nutrients, they produce the enzymes necessary for their absorption.
Even the plants are sensitive to different types of chemical and physical stimuli; their activities, for example, change from day, during which produce the substances they need through photosynthesis, to night, during which such activity stops. Plants are moreover able to do much more: it was found that in the presence of an invasion by pests, some plants not only have a chemical reaction of defense, but also emit in the air substances that, perceived by the other plants, activate their defenses enabling them to anticipate the attack. It is therefore a genuine chemical communication consisting of stimuli and appropriate reactions.
In the animal world, where for surviving it is necessary to identify a prey or a predator, the greater need to perceive and react led to the formation of the sense organs and nervous system. Thanks to the bodies specialized in the perception of certain stimuli, the animals manage to locate their prey or their predators, feel the presence of their own kind and many other things. Very early in their history, animals have developed a system to manage the amount of information from their senses and to give a comprehensive interpretation: this is the nervous system, which is formed by neurons, very specialized cells capable of transmitting electrochemical signals at high speed to one another.
The neurons form in the body real communication channels, through which the stimuli perceived by the senses are transmitted to the brain, that is a sort of centre of coordination determining the most appropriate reaction. This latter, in some cases, may necessarily result in a given motion.
The brain then manages the sensations and accordingly guides the movements of the body, but also performs many other functions; among them, two have a fundamental importance: memory and learning.

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