5—Physical Development in Infancy

1. 5—Physical Development in Infancy • Body Growth and Change • The Brain • Sleep • Health • Summary

2. Body Growth and Change • Growth Patterns • Cephalocaudal pattern: • The sequence in which the greatest growth occurs at the top—the head—with physical growth in size, weight, and feature differentiation gradually working from top to bottom. • Proximodistal pattern: • The sequence in which growth starts at the center of the body and moves toward the extremities.

3. Body Growth and Change Changes in Proportions of the Human Body During Growth • Refer to Figure 5.1

4. Body Growth and Change • Infancy and Childhood • Infancy • The average North American newborn is 20 inches long and weighs 7½ pounds. • Most newborns lose 5% to 7% of their body weight in the first several days of life. • Newborns double their birth weight by the age of 4 months and nearly triple it by their first birthday, but growth slows in the second year; by age 2, children average 32 to 35 inches in height—nearly half their adult height.

5. Body Growth and Change • Infancy and Childhood • Early Childhood • The percentage of increase in height and weight decreases each year for preschoolers, and girls are only slightly smaller and lighter than boys. • Body fat declines slowly during preschool years; girls have more fatty tissue than boys and boys have more muscle tissue than girls • Growth patterns vary due to heredity and environmental experiences.

6. Body Growth and Change • Infancy and Childhood • Early Childhood • Physical problems, growth hormone deficiency, or emotional difficulties may retard growth. • Growth hormone deficiency: The absence or deficiency of growth hormone produced by the pituitary gland. • Can be treated with injections of growth hormone for several years.

7. Body Growth and Change • Infancy and Childhood • Middle and Late Childhood (Ages 6 to 11) • Slow, consistent growth averaging 2 to 3 inches a year. • Muscle mass increases; body fat decreases. • Improved muscle tone and strength. • Bones continue to harden.

8. Body Growth and Change • Puberty • A period of rapid physical maturation involving hormonal and bodily changes that take places in early adolescence. • Determinants of Puberty • There are wide variations in onset and progression. • Age of onset has been steadily dropping around the world, with average age of menarche dropping 2 to 4 months per decade during the twentieth century.

9. Body Growth and Change – Determinants of Puberty (continued) • Menarche: A girl’s first menstruation, with normal age ranging from 9 to 15 years old. • Timing for the emergence of puberty is hereditary, but is influenced by environmental factors such as health, weight, and stress.

10. Body Growth and Change • Determinants of Puberty (continued) • Hormones: Powerful chemical substances secreted by the endocrine glands and carried through the body by the bloodstream. • In puberty, secretion of key hormones is controlled by the interaction of the hypothalamus, the pituitary gland, and the gonads (sex glands).

11. Body Growth and Change • Determinants of Puberty (continued) • Adrenarche involves hormonal changes in the adrenal glands (about ages 6 to 9). • Gonadarche involves sexual maturation and the development of reproductive maturity . • Culmination of gonadarche in girls is menarche (first menstruation), in boys is spermarche (the first ejaculation of semen).

12. Body Growth and Change • Determinants of Puberty (continued) • Key hormonal changes of gonadarche are androgens (main class of male hormones, e.g., testosterone) and estrogens (main class of female hormones, e.g., estradiol). • These hormones are present in both males and females, but in different concentrations. • Growth during puberty is facilitated by hormones such as cortisol, testosterone, and estrogen.

13. Body Growth and Change Hormone Levels by Sex and Pubertal Stage for Testosterone and Estradiol • Refer to Figure 5.2

14. Body Growth and Change • Puberty (continued) • Weight and Body Fat • Undernutrition can delay puberty: for menarche to begin and continue, fat must make up 17% of a girl’s body weight. • Amenorrhea, an absence or suppression of menstruation, occurs in anorexic adolescents and females participating in some sports. • Leptin, a hormone released by fat cells, signals the adequacy of fat stores for reproduction and maintenance of pregnancy at puberty.

15. Body Growth and Change • Puberty (continued) • Growth Spurt • Occurs approximately 2 years earlier for girls than for boys. • Mean beginning of the growth spurt in the U.S. is age 9 for girls and age 11 for boys. • Height and weight follow approximately the same timetable, and 50% of adult body weight is gained during adolescence. • Girls increase in hip width, boys increase in shoulder width.

16. Body Growth and Change Pubertal Growth Spurt • Refer to Figure 5.3

17. Body Growth and Change • Puberty (continued) • Sexual Maturation • The three most noticeable areas of sexual maturation in boys include penis elongation, testes development, and growth of facial hair. • The two most noticeable areas of sexual maturation in girls include breast enlargement and the appearance of pubic hair. • Menarche occurs late in the pubertal cycle.

18. Body Growth and Change • Puberty (continued) • Body Image: • Adolescents are preoccupied with their bodies. • Girls are generally less happy than boys with their bodies.

19. Body Growth and Change • Puberty (continued) • Early and Late Maturation • Early-maturing adolescents have more positive body image than late-maturing adolescents, but by their 30s, late-maturing boys have a more positive identity than early-maturing boys. • Early-maturing girls have an increased vulnerability to socioemotional problems.

20. Body Growth and Change Normal Range and Average Development of Sexual Characteristics in Males and Females • Refer to Figure 5.4

21. Review and Reflect: Learning Goal 1 • Discuss developmental changes in the body • Review • What are cephalocaudal and proximodistal patterns? • What changes in height and weight take place in infancy and childhood? • What changes characterize puberty?

22. Review and Reflect: Learning Goal 1 • Reflect • Did you experience puberty early, late, or on-time? How do you think this affected your social relationships and development?

23. The Brain • Brain Physiology • The brain has two hemispheres. • The forebrain, or top portion, is covered by a layer of cells called the cerebral cortex, which is responsible for 80% of the brain's volume; it is critical in perception, thinking, language, and other functions.

24. The Brain • Brain Physiology (continued) • Four lobes of the cortex: • Frontal lobes: Govern voluntary movement, thinking, personality, and intentionality or purpose. • Occipital lobes: Control vision. • Temporal lobes: Govern hearing, language processing, and memory. • Parietal lobes: Govern spatial location, attention, and motor control.

25. The Brain The Human Brain’s Hemispheres • Refer to Figure 5.5

26. The Brain The Brain’s Four Lobes • Refer to Figure 5.6

27. The Brain • Brain Physiology (continued) • Limbic System • Hypothalamus (monitors eating, drinking, and sex) • Pituitary gland (controls growth, regulates other glands) • Amygdala (governs emotions) • Hippocampus (governs memory and emotion)

28. The Brain • Brain Physiology (continued) • Neuron • Nerve cell that handles information processing at the cellular level. • Axons send electrical signals away from the central part of the neuron, across synaptic gaps, via chemical substances called neurotransmitters. • Dendrites of different neurons receive the signals. • Myelin sheath: Layer of fat cells that helps impulses travel faster along the axon.

29. The Brain The Neuron • Refer to Figure 5.7

30. The Brain • Brain Physiology (continued) • Neural circuits are clusters of neurons that work together to handle particular types of information. • The neural circuit for attention and working memory uses the neurotransmitter dopamine and lies in the prefrontal cortex.

31. The Brain The Prefrontal Cortex • Refer to Figure 5.8

32. The Brain • Brain Physiology (continued) • Lateralization • Specialization of function in one hemisphere of the cerebral cortex or the other. • Complex thinking requires both hemispheres.

33. The Brain: Infancy • Brain development occurs extensively in utero. • Because of the extensive brain development during infancy, the infant’s head must be protected. • Shaken baby syndrome: Damage to brain from shaking a baby, includes brain swelling and hemorrhaging.

34. The Brain: Infancy • Early Experience and the Brain • Depressed brain activity has been found in children who grow up in a deprived environment (Cicchetti, 2001), and it’s possible the effects are irreversible. • Neuroscientists believe that what wires the brain is repeated experience: • Before birth, genes direct wiring patterns. • After birth sensory and environment input shape neural connections.

35. The Brain: Infancy Early Deprivation and Brain Activity • Refer to Figure 5.9

36. The Brain: Infancy • Changing Neurons • Myelination, the process of encasing axons with fat cells, begins prenatally and continues after birth. • Among the most dramatic changes in the brain in the first 2 years of life are the increases in synaptic connections, with synaptic blooming and pruning.

37. The Brain: Infancy • Changing Structures • The frontal lobe is immature at birth, but increased myelination and neural connections during the first year enhance the ability to regulate physiological states and gain more control over reflexes. • 2 months: development of motor control centers allow reaching and grabbing. • 4 months: neural connections for depth perception begin to form. • 12 months: speech centers ready to produce language.

38. Infancy The Development of Dendritic Spreading • Refer to Figure 5.10

39. The Brain: Infancy Synaptic Density in the Human Brain from Infancy to Adulthood • Refer to Figure 5.11

40. The Brain: Childhood • Brain growth is slower than in infancy, but the brain and the head grow faster than other parts of the body. • Increase, due to myelination (which is not complete until the end of middle or late childhood), in number and size of dendrites. • Most rapid growth from age 3 to 6 is in frontal lobe areas (planning and organizing new actions and maintaining attention to tasks). • Most rapid growth from age 6 through puberty is in temporal and parietal lobes, especially for language and spatial relations.

41. The Brain: Adolescence • Adolescents process emotional information primarily in the amygdala (emotion-processing area) rather than in the frontal lobe (higher-level reasoning and thinking area); the reverse occurs in adults. • The adolescent prefrontal cortex is not yet developed to control strong emotions (Nelson, 2003). • Areas of the limbic system involved with reward and pleasure lead adolescents to seek novelty and to need higher levels of stimulation to experience pleasure. • Slow development of prefrontal cortex means a lack of cognitive skill for controlling pleasure seeking, which may explain increased risk-taking and other problems.

42. Review and Reflect: Learning Goal 2 • Describe how the brain changes • Review • What is the nature of brain physiology? • How does the brain change in infancy? • What characterizes the development of the brain in childhood? • How does the brain change in adolescence and how might this change be linked to adolescent behavior?

43. Review and Reflect: Learning Goal 2 • Reflect • Claims are made that elementary and secondary education should be brain-based. Some journalists suggest that educators look to neuroscientists for answers about how best to teach children and adolescents. Such statements are speculative and far removed from what neuroscientists know. Find an article on brain-based education in a magazine or on the Internet. Use your critical thinking skills to evaluate the article’s credibility. Does the author present research evidence to support the link between neuroscience and the brain-based method being recommended? Explain.

44. Sleep • Sleep restores, replenishes, and rebuilds the brain and body. • Some neuroscientists believe that sleep allows neurons that have been used during waking to shut down and repair themselves.

45. Sleep: Infancy • Newborns sleep 16 to 17 hours a day, although some sleep more and others sleep less. • By age 1 month most infants sleep longer at night. • By age 4 months their patterns are closer to adult sleep patterns. • There are cultural variations in sleep patterns.

46. Sleep: Infancy • REM Sleep • Adults spend about one-fifth of their night in REM sleep and it usually appears about 1 hour after non-REM sleep. • About one-half of an infant’s sleep is REM sleep, and infants often begin their sleep cycle with REM sleep rather than non-REM sleep. • REM sleep might promote the brain’s development in infancy.

47. Sleep: Infancy Sleep Across the Human Life Span • Refer to Figure 5.12

48. Sleep: Infancy • Shared Sleeping • Sharing a bed with a mother is a common practice in many cultures. • Shared sleeping remains a controversial issue.

49. Sleep: Infancy • SIDS • Sudden infant death syndrome (SIDS)—A condition that occurs when an infant stops breathing, usually during the night, and suddenly dies without an apparent cause. • SIDS decreases when infants sleep on their backs. • Risk factors include low birth weight, a sibling who has died of SIDS, sleep apnea, being African American or Eskimo, lower socioeconomic status, exposure to cigarette smoking, and soft bedding.

50. Sleep: Childhood • Most young children sleep through the night and have one daytime nap, although they may try to drag out their bedtime routine. • Sixth-graders go to bed an hour later than second-graders and report more daytime sleepiness. • Sleep problems: Nightmares (frightening dreams that awaken the sleeper) and nightterrors (sudden arousal from sleep with intense fear and physiological reactions) are common sleep problems.