Chapter 6. Analyzers

A living organism constantly perceives the effects of the external and internal environment. The totality of excitable structures in peripheral and central nervous systems providing perception and analysis of the effects caused by the external and internal environment is called analyzers.

All the structures affiliated with analyzers are afferent, i.e., conducting stimulations from the periphery to central nervous system. Analyzers "decompose" external world into elements, and then transform excitation into sensation, after which the body forms a certain behavioral tactic. According to I.P. Pavlov, cells of cerebral cortex carry out the highest analysis and synthesis of the internal and external environmental effects.

Various stimuli of the external world, acting upon a living organism, shape a specific response in its CNS that determines the psychological reflection phenomenon. There exist several levels of reflection. First one is sensation, the reflection of stimulus individual properties, second - perception, the process of analyzing and synthesizing individual sensations by comparing them with previous experience, and finally, representation - creation of images without direct impact of the stimulus on sensory organs. The processes of psychological reflection are provided by specific apparatus - analyzers. The analyzer is a set of excitable structures of the peripheral and central nervous systems that analyze external stimuli with subsequent synthesis of a mental image.

Analyzers in systemic organization of behavior

Analyzers in systemic organization of physiological functions are dynamic self-adjusting and self-regulating organizations. From the systemic point of view, afferent excitation pathways always have a specific functional value in the formation of behavior. They differ not only in sensory modality of afferent excitation, but also in their role in mechanisms of systemic architectonics of behavioral acts, in particular, in mechanisms of afferent synthesis and apparatus for anticipating action results. In the systemic organization of behavior, the following afferent excitations are distinguished: situational afferentation, triggering afferentation, and reverse afferentation.

Situational afferentation

Participates in developing stage of afferent synthesis. It includes the entire set of external factors affecting the body that make up a specific situation, which underlies the shaping of a behavioral act. In relation to a person, numerous social factors act as situational stimuli: moral, cultural, domestic, etc.

Triggering afferentation

Triggering afferentation is interpreted as afferent excitations that occur when stimuli, which directly trigger a behavioral act affect the body. Various conditioned stimuli and time can act as trigger stimuli.

Reverse afferentation

Afferent excitations bring information to the brain structures about a sudden demand in the body and the success of achieving the results of purposive behavior. In the body functional systems, reverse afferentation in the form of nervous impulses from interoreceptors and humoral influences on the nervous system centers constantly signals the level of achieving results useful for the body, in particular, the optimal level of certain internal environment indicators. In any behavioral act that is aimed at obtaining any adaptive, i.e., useful result for the body, reverse afferentation informs about this result of the performed action, allowing the entire body to assess the success level of the action performed and correct errors in a timely manner. For example, a person may have an intention to drink a glass of tea based on metabolic processes and interaction of the body with the external environment. One stretches out a hand to the glass of tea, takes it. Tactile stimulation of the palm by the glass surface, temperature, weight, and finally, visual irritation from the hand-glass contact - all these afferent stimuli in total provide feedback that the result of the action corresponds to the original intention. In addition, during the implementation of this action, the very movement of the hand to the glass is continuously regulated by proprioceptive signaling, indicating the correct and appropriate distribution of the contracted muscles, degree of hand tension, height of its position in relation to the intended goal, etc.

Guiding and effective reverse afferentation

Reverse afferentation that occurs during a motor action is divided into two different categories: guiding movement and productive afferentation. Guiding afferentation is mainly represented by impulses from muscle proprioceptors that carry out the movement, productive afferentation is always complex and may include afferent pathways from retinal photoreceptors, tactile, taste, auditory, and other receptors. In turn, reverse productive afferentation is divided into a step-by-step reverse afferentation and a sanctioning reverse afferentation, which occurs when the subject reaches the desired result, retains the most successful integration of afferent excitations and completes the functional systemic quantum of behavior (for example, "I want to drink" - "I have drunk enough").

I.P. Pavlov's classical concepts describing the analyzer include three parts: peripheral division, conductive division, and central division. The peripheral division consists of receptors, an additional apparatus, and a primary afferent neuron. The conductive division consists of sensitive nerves and specific afferent pathways of the spinal cord and brain stem. The central division represents areas of cerebral sensory cortex where excitations of a particular