1.1. Nervous system: general structure
The nervous system is a system of the body that combines and regulates various physiological processes in accordance with the changing conditions of the external and internal environment. The nervous system perceives sensory stimuli, processes information and creates the body’s response to external and internal stimuli (behavior). Special types of information processing are learning and memory, thanks to which we can adapt our behavior to the changing environment taking into account previous experience. Other systems, such as the endocrine and immune systems, are also involved in these functions. The nervous system plays main role in coordinating the functioning of all anatomical structures of the body in exact accordance with the actual settings and transformation of the external environment. The nervous system as an integrating system appears only at a certain stage of the evolutionary development. The behavior of the simplest organisms is based on special principles (taxis). Thanks to the nervous system, organisms have a fundamentally different form of behavior organization based on reflexes. The reflex principle of behavior organization allows you to respond more accurately to external and internal stimuli. Beside the innate behavioral mechanisms (innate reflexes), the most important role in evolution belongs to the factors of learning (acquired reflexes), which leads to the formation of the highest form of behavior — the mind, the ability to program and control one’s activities. A set of behavioral acts associated with the speech is especially important for human.
The nervous system consists of the following parts:
- sensory, reacting to stimuli coming from the environment;
- integrative, processing and storing sensory and other data, motor, controlling movements;
- vegetative, regulating the constancy of the internal environment of the body and the secretory activity of the secretory organs.
The functions of the nervous system are extremely diverse. It unites all organs and systems into a functionally unified organism and ensures the interaction of the organism with the external environment. Via the sensory organs and nerve endings of the skin, mucous membranes, and the musculoskeletal apparatus, the nervous system is able to receive a variety of sensory information that arises as a result of irritation of these perceiving sensory structures (receptors). The sensitive nerve cells transmit nerve impulses arising during their irritation to the spinal cord and brain (afferent sensory systems), where received information is processed.
The processing of information in the nervous system means the following processes:
- transmission of information in neural networks;
- transformation of signals by combining them with other signals (neural integration);
- storing information in memory;
- extracting information from memory;
- using sensory information for perception;
- cognition;
- training;
- planning (preparation);
- execution of motor commands;
- formation of emotions.
Interneural interactions occur through both electrical and chemical processes. After a multifaceted processing of nervous excitement in the spinal cord and brain, the information is transmitted to motor and vegetative cells (efferent systems), leading to the excitation of effector organs (muscle contraction, narrowing or dilation of blood vessels, changes in the work of internal organs). To be noticed is that the incoming stimuli differ in their degree of significance and complexity and are closed at different levels of the nervous system depending on the need to connect the higher integrative cortical centers.
The functioning of the nervous system is based on the principle of vertically organized hierarchical subordination of neural networks structurally and functionally connected to various regions of the brain.
The nervous system is divided into:
- central;
- peripheral (Fig. 1.1).
The central nervous system (CNS) consists of the brain and spinal cord. The peripheral nervous system (PNS) includes roots, plexuses, and nerves.