Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

The Nervous System (general structural and developmental plan of the nervous system)
Central Nervous System
Higher Nervous Activity — Age-Related Features of Human Higher Nervous Activity

The electrical activity of the brain (EEG) reflects The activity of subcortical brain structures. During the first 3–4 months of life, a slow rhythm (delta rhythm) predominates. The Emergence of a faster alpha rhythm during ontogenesis occurs gradually. Between the ages of 6 and 8 years, the frequencies of the alpha rhythm stabilize. By 11–12 years, the alpha rhythm becomes the dominant rhythm in the EEG. At 15–16 years of age, the resting EEG closely resembles that of an adult in its characteristics.

Development of conditioned Reflexes. A child is born with a specific set of innate, unconditioned reflex reactions. Starting from the 2nd day of life, conditional connections begin to form, facilitating ADAPTATION TO ENVIRONMENTAL conditions. One of the earliest responses (developing on days 2–5) is the feeding-position reaction, manifested through HEAD movements, sucking, and other motor activities. On the 2nd day after birth, the orienting reflex emerges, which in newborns consists of the cessation of sucking in response to various stimuli.

The first positive conditioned reflexes in newborns can be established by the 7th day on The basis of unconditioned food reflexes. During the second month of life, many conditioned reflexes can be successfully formed.

With age, the rate at which conditioned reflexes are acquired increases. In preschool children, a stable conditioned reflex is formed after 10–20 pairings, whereas in early school-age children, it requires only 2–15 pairings.

External unconditioned inhibition appears in infants from the very first days of life. In response to a strong external stimulus, such as a loud sound, the infant stops sucking the breast. In subsequent years, the Influence of External inhibition on a child's conditioned reflex activity gradually diminishes. This is associated with an increased rate of inhibition of orienting reflexes. By ages 6–7, The Significance of external inhibition for Higher nervous activity decreases, while The Role of internal inhibition increases.

Internal inhibition develops in a child around the 20th day after birth, representing a primitive form of differential inhibition. Throughout life, differential inhibition undergoes continuous "refinement." Initial signs of extinction inhibition are noted at 2–2.5 months, conditioned inhibition is observed at 2.5–3 months, and delayed inhibition—which serves as the foundation for strength, willpower, and self-control—appears around 5 months. The Development of all these types of inhibition is a rather complex task for the child. The establishment of internal inhibition serves as the physiological basis for upbringing and acts as a prerequisite for the rapid acquisition of numerous conditioned reflexes.

Based on the dynamic stereotype, a child develops abilities, skills, and habits—that is, the need to execute specific reflexes. Conditioned reflexes formed during this period are exceptionally durable, and modifying them is extremely difficult. Therefore, it is crucial to employ correct educational approaches from the very first years of life.

The developmental timelines of sensory and motor speech in ontogenesis do not coincide, with the development of sensory speech preceding that of motor speech. Even before a child begins to speak, they already understand the meaning of words. Speech development comprises the following stages: 1) the preparatory stage, or the stage of producing individual sounds and syllables (from 2–4 to 6 months); 2) the emergence of sensory speech, i.e., the appearance of the first signs of a conditioned reflex to a word and its meaning (6–8 months); 3) the emergence of motor speech, i.e., the utterance of meaningful words (10–12 months).

By 12 months, a child's vocabulary consists of 10–12 words; by 18 months, 30–40 words; by 24 months, 200–300 words; by 36 months, 500–700 words; and in some cases, up to 1,500 words. By 6–7 years of age, the capacity for inner (semantic) speech—that is, thinking—emerges.

Mental modeling of various events by an individual constitutes The Essence of thinking. Action-oriented (sensorimotor) thinking develops during the preschool and early school years. Verbal-logical (theoretical) thinking manifests around 8–9 years of age and reaches full maturity by 14–18 years.

Review and Self-Assessment Questions:

1. Discuss the Classification and Mechanisms of Memory.

2. Discuss the Types of Higher nervous activity and the roles of heredity and upbringing in their formation.

3. Discuss the age-related characteristics of higher nervous activity.