Due to the presence of a second, nonspecific afferent system of the ANS, the afferent innervation performs not only the passive function of switching off (inhibition) of the efferent part of the unconditioned reflex arc, but also an active function – inhibition of the central structures of the ANS. This function is provided by pacemakers in each small group of cells from which a single nerve fiber originates. Apparently, most of the time, it is the afferent fibers of the ANS that function, supporting with their signaling through the second, nonspecific afferent system, the inhibited state of the cells of the nuclei of the brain stem (including the hypothalamus).
In addition to the specific afferent system, there is a second or nonspecific afferent system. Information from peripheral sensory nerve endings, represented by many types of receptors (baroreceptors, mechanoreceptors, chemoreceptors, thermoreceptors) in this system is depersonalized, coming through collateral connections to the same neurons.
All nerve signals sent to the central nervous system along the sensory pathways of the nonspecific afferent system enter the reticular formation, which takes part in the activation of the cerebral cortex and in the control of the spinal cord. Signals from the periphery keep the reticular formation in a retarded state.
Signals entering the reticular formation from the cerebral cortex, for example, during stress or upon awakening, activate the reticular formation, thereby providing an integral response of the body to stress or to the initiation of wakefulness.
The nonspecific afferent nervous system of the ANS is an important part of the system of regulation of adaptation metabolism, which makes it possible to increase its rate tenfold.
The property of the most vulnerable link of autonomic innervation, afferent nerve fibers “owe” to several features.
1) The peripheral part of the afferent system of innervation is a “servant of two states” – the sympathetic and parasympathetic divisions of the ANS, working alternately, and the “master” of the central division of the ANS, participating in the regulation of its work through the second nonspecific afferent system. Afferent connections of the ANS function around the clock, which leads to their primary depletion and degeneration.