The nervous system of living organisms, due to its properties, not only regulates the activity of the whole organism and reaction to internal or external changes, but also provides an opportunity for the development of the psyche. One of the key functions of nerve cells is irritability. Why is it needed?
Irritability (excitability) is the property of cells, tissues, organs and intracellular formations to respond to various changes in factors of the internal and external environment (stimuli) by a shift in functions and structures. The perception of irritation is denoted by the term reception (perception). This property ensures the adaptability of living organisms to changing environmental conditions. Irritability of primitive organisms (microbes, protozoa), as well as certain cells (sperm, white blood cells) is reflected in taxis - the ability to move relative to the stimulus. In plants, excitability is manifested in the form of motor reactions, as well as in reactions to gravity, the chemical composition of the environment, electrical or mechanical stimulation, light, and the Earth's magnetic field. Plants, as you know, do not have the sense organs inherent in animals and humans, but they have receptor proteins and cells by which plants respond to stimuli. An example of irritability in plants is sunflower following its head after the sun. In a normal state, a plant cell has a negative electrical potential ranging from -50 to -200 mV. In response to the stimulus, a positive reaction occurs that can exceed the resting potential or equal to it. If the external effect on the cells was superstrong, this can lead to the death of the plant. People and animals are characterized by a variety of reactions to various kinds of stimuli, which is provided by reflexes, higher nervous activity and consciousness. The excitability of complex organisms is manifested mainly in a sensitive perception of the events of the surrounding world with the help of sensory organs (receptors). Effects on receptors through nerve impulses transmit information to the corresponding parts of the brain. And then the brain gives "orders" to one or another organ, effectively regulating the processes of life. Thus, irritability is one of the indicators of the body's reactivity. Reactivity is a mechanism laid down by nature itself, aimed at preserving and developing not only each type of living organism, but also its specific individual.