The Child's Growth: Brain, Body, Motor Skills, and Sexual Maturation
The Child's Growth: Brain, Body, Motor Skills, and Sexual Maturation
BRAIN DEVELOPMENT IN INFANCY
The largest portion of the human brain, the cerebrum, is covered by a highly convoluted layer called the cerebral cortex. The cortex is divided into a number of regions whose cells control specific functions such as seeing, hearing, feeling, moving, and thinking.Neurons and Synapses
In the developing organism, neuron proliferation rapidly increases the brain's nerve cells, or neurons. Although all the brain's neurons are present at birth, many subsequent changes take place in the size of neurons, the numbers of connections, or synapses among them, and the production of the surrounding, supportive glial cells. These changes, such as myelination, increase the speed, efficiency, and complexity of transmissions between neurons.Sequential Development of the BrainNeural migration distributes neurons throughout brain regions. The abundance of synapses, formed by synaptogenesis, and of neurons is trimmed over time through the processes of neuronal death and synaptic pruning.Hemispheric Specialization
The human brain is organized in two halves; the two brain hemispheres are connected by the corpus callosum. The right hemisphere controls the left side of the body and is involved in the processing of visual-spatial information, face recognition, and interpreting emotional expressions. The left hemisphere controls the right side of the body and is important for understanding and using language. Both hemispheric specialization and lateralization are evident early in infancy and are well developed by age 3.Dyslexia, or difficulty in learning to read, may reflect abnormal lateralization patterns, such as the processing of spatial information on both sides of the brain rather than primarily in the right hemisphere, the normal arrangement.The Brain's Plasticity
The environment plays a critical role in brain development. In rats, enriched environments that permit a great deal of activity and exploration are related to increases in brain size, in the number of connections among neurons, and in the activities of key brain chemicals. Apparently, the brain has great plasticity, which allows it to compensate for defects or damage in one area or even one hemisphere.
MOTOR DEVELOPMENTReaching and Grasping
Research suggests that infants grasp objects in a variety of different ways, depending on the object's size and shape and the relative size of their own hands. This research indicates that the infant motor system is highly flexible and able to adapt to the demands of the situation.
Research based on dynamic systems theory has shown that patterns of specific reaching and grasping behavior reflect both coordination tendencies in an infant's general, nonreaching arm movements and environmental influences such as task requirements.Locomotion
The development of walking follows a U-shaped course, beginning with a stepping reflex at birth that disappears in a few months; that is followed by the emergence of independent, voluntary walking a number of months later, usually around the first birthday.
A dynamic systems approach to explaining this pattern suggests that the development of walking depends on the combined readiness of a variety of factors, and when the baby's weight becomes too much of a load on the emerging motor system, stepping ability may be temporarily masked. Cross-cultural studies indicate that environmental influences, such as repeated practice of a skill, may either enhance or slow a complex motor skill like independent walking.The Role of Experience and Culture
The relations between locomotion, other aspects of development such as perception, social interaction, and problem solving, and environmental forces are complex. In general, the greater a child's motor skills, the more his general development is enhanced; at the same time, negative factors such as conflicted child-parent relations may sometimes promote developmental skills, such as walking.
Infants' and children's growth is guided by two basic principles. According to cephalocaudal development, growth proceeds from the head downward, and following the proximal-distal pattern, development occurs from the center outward. In addition, growth proceeds at different rates during different stages of development. Growth is fastest during the first six months of life.Do Genes Affect Height and Weight?
Adult height is difficult to predict from a baby's size, which tends to be more closely related to the size of the mother. Successful predictions can be made in later childhood based on the child's current height, gender, and parents' heights.The Influence of Environmental Factors
Inadequate nutrition may result in severely depressed growth rates. During World Wars I and II, height, weight, and age of puberty were affected by lack of adequate nutrition. Other environmental factors that may affect growth rates include illness, disease, and climate.
Environmental influences such as nutrition and housing interact with other factors to produce a considerable variation in growth rates among people of different nationalities, ethnicities, and socioeconomic class. The effects of poverty may be seen in such disorders as iron-deficiency anemia, common in minority children and children in low-income countries.
Following environmental injury or deprivation, a strong corrective principle appears to operate in the case of physical growth. The degree of catch-up growth will depend on such things as the duration, severity, and timing of the deprivation, in addition to the nature of the subsequent treatment or therapy. In general, the earlier and more prolonged the malnutrition, the more difficult it is to regain a normal level of growth.People are Growing TallerSecular trends in many countries show that across evolution people have become taller. Although in the United States people in the most advantaged groups may have reached their maximum potential in height gain, people in other segments of society continue to grow taller; both genetic and environmental factors influence this growth tendency.Are We Growing Heavier? Obesity and Eating Disorders
Although the problem of obesity may begin in infancy and childhood, only about one-quarter of obese infants will remain obese 20 years later. The two critical periods for the development of obesity are during infancy and at about 4 years of age. Recent research indicates that genetic factors may play a role in determining later obesity; however, parents' strategies for getting their children to eat may contribute as well.
In addition to physical problems, such as hypertension and diabetes, obese children and adolescents may experience body-image disturbances and may suffer discrimination by peers and adults. Effective diet programs for children have focused on changing the eating patterns and exercise behavior of both the child and other family members.
Dieting disorders include anorexia nervosa, which may occur early in adolescence and results from reduced intake of calories, and bulimia nervosa, which typically occurs in later adolescence and is characterized by food binges and purging through vomiting.
SEXUAL MATURATIONThe Onset of Sexual MaturityPuberty, the attainment of sexual maturity, is triggered when the pituitary gland stimulates other endocrine glands to secrete hormones, including estrogens and progesterone in females and testosterone in males, that initiate a growth spurt. This milestone in growth is marked by changes such as the start of breast development and menarche in girls, and the enlargement of the testes and spermarche in boys. Girls tend to reach menarche earlier in the more advanced countries, but there is still considerable variation in the onset of menstruation throughout the world.What Determines the Timing of Puberty?
Inheritance is a strong factor in the timing of menarche, although environmental conditions such as conflict within the family and absence of the father may also exert an influence on when a young girl reaches menarche.The Effects of Early and Late Maturation
The timing of physical maturation can affect the child's social and emotional adjustment. Research indicates that the effects for late-maturing boys and early-maturing girls are largely negative. In general, the impact of the timing of puberty is best understood in the context of other transitions, such as school transitions and family disruptions, which may help or hinder the child's ability to cope with biological changes.
There are wide individual differences in rates of maturation. However, in general, girls mature earlier than boys; on average, major changes occur two years earlier for girls. Although early maturation is usually seen as advantageous for boys, girls sometimes find early maturation stressful, developing poor body images and engaging in so-called adult behaviors such as drinking and smoking at an early age.