8 Higher nervous activity. Reflexes. Reflex classification. Conditions and mechanisms of formation of conditioned reflexes.

According to I.P. Pavlov's concept of “higher nervous activity” was intended to replace the former term “mental activity”. The physiology of higher nervous activity sets itself the task of studying the patterns and mechanisms of the brain, through which the organism interacts with the external and internal environment.
Higher nervous activity (GNI) is the activity of the higher nervous system, it is peculiar to all creatures with the central nervous system, and includes the mechanisms of perception of the external world, as well as the mechanisms of behavior.
The structural basis of higher nervous activity in mammals is the cerebral cortex and a number of subcortical structures. The evolutionary complication of higher nervous activity is associated with an increase in the associative zones of the cortex. In humans, the improvement and complication of higher functions proceeded in parallel with an increase in the size of the associative zones of the parietal, temporal, and frontal lobes of the cortex. They are the material substrate of human consciousness and thinking.
The basis of the theory of higher nervous activity is the work of I.M. Sechenov, brilliantly continued by I.P. Pavlov, who developed a coherent theory of GNI.
The substrate or material basis of higher nervous activity is the brain. This phrase now seems banal, but not always mental functions associated with the brain. In ancient Egypt, when the body of the famous Egyptians was mummified, the heart, liver, stomach were honorably placed in special vessels, and the brain — an ordinary-looking, slippery gray matter — was removed through the left nostril and thrown away. It was not the brain that was considered the repository of feelings, thoughts, and experiences, but completely different organs.
Reflex - the response of the body to stimulation by the central nervous system. The realization of the reflexes is provided by the nervous elements forming the reflex arc. Reflex arc - the path along which nerve impulses pass from the receptor to the working organ. From the receptor to the central nervous system, impulses travel along the sensitive path, and from the central nervous system to the working organ along the motor path. The reflex arc has the following components:

receptor (end of dendrite sensitive neuron; perceives irritation),
afferent sensory (centripetal) nerve fiber (transmits excitation from the receptor to the central nervous system),
nerve center (a group of intercalary neurons located at different levels of the central nervous system; it transmits nerve impulses from sensory nerve cells to motor ones),
efferent motor (centrifugal) nerve fiber (transmits excitation from the CNS to
the executive body (muscle, gland) whose activity changes as a result of the reflex).
A simple reflex arc consists of two neurons: the sensory and the motor (for example, the knee jerk).
Complex reflex arc - from the sensitive, one or more intercalary and motor. Through the intercalary neurons, the feedback between the working organ and the central nervous system is carried out, the adequacy of the response of the working organ to the stimulation obtained is monitored.
Reflex classification
First, there are unconditional (innate) and conditioned (acquired in the process of life) reflexes.
In addition, reflexes can be classified
1) by biological significance: defensive or protective food, sexual, approximate or research,
2) according to the location of the receptors,
3) according to the part of the brain in which the reflex arc closes: spinal if in the spinal cord, bulbar, if in the medulla, etc.
4) the nature of the response: motor, secretory trophic (ie, providing a change in the metabolic processes in the body).
Unconditioned reflexes are innate, permanent, hereditarily transmitted reactions characteristic of representatives of this type of organism. For example, pupil, knee, Achilles and other reflexes. Some unconditioned reflexes are performed only at a certain age, and then they die out (for example, sucking, prehensile, sexual reflexes, the Babinski reflex).
Unconditioned reflexes - the basis for the development of conditioned reflexes in animals and humans.
Conditioned reflexes are adaptive, temporary and strictly individual reactions. They may be inherent in only one or several members of the species subjected to training (training or exposure to certain environmental conditions.
Conditioned reflexes are developed gradually in the presence of
mature cerebral cortex and lower parts of the brain. The following conditions are necessary for their formation:
1) the action of the conditioned stimulus must precede the action of the unconditioned,
2) reinforcement of the conditioned stimulus by the unconditioned must be combined more than once,
3) there should be no distracting stimuli in the development of a reflex,
4) the normal waking state of the cerebral cortex is necessary.