4.1. Reflex principle of the nervous system
A reflex is a reaction of the body occurring with participation of the nervous system in response to receptor stimulation. A reflex is activation or inhibition of the activity of organs; it is the most important mechanism of adaptation of an organism to environmental conditions. I.P. Pavlov proposed to divide reflexes into two types, unconditional and conditional ones.
Unconditional reflexes provide for lower nervous activity regulating the body?s functions and its instinctive behavior in a relatively constant external environment. Unconditional reflexes emerged in the process of phylo-genetic development of the species, i.e. they are species reflexes and are passed from parents to offspring.
Individual adaptation of an organism to constantly changing environmental conditions is provided by conditioned reflexes, which reflect individual experience of a person. Conditioned reflexes are described in Chapter 32.
The key stages of studying reflexes were as follows: R. Descartes (18th century) developed a mechanistic concept of the reflex (under the influence of an irritant, ?nerve filaments? attached to the nerves of the brain
are stretched, and valves open. Through these valves ?animal spirits? (streams of minute particles directed to the muscles and inflating them) pass to the nerves; physiologists of the 18th and 20th centuries (J. Prokhazka, I.M. Sechenov, I.P. Pavlov and others) developed an experimentally confirmed theory of cerebral operation based on unconditioned and conditioned reflexes. However, reflex activity is the body?s response to the past and present (elements of prediction of the future are contained in conditioned and dominant reflexes). In the late twentieth century, studies by Russian physiologists (P.K. Anokhin, K.V. Sudakov and others) developed the theory of functional systems explaining the organisms response to future events.