1. Chapter Four
PHYSICAL DEVELOPMENT

2. The Brain and Nervous System
System develops rapidly during first 2 years
Midbrain and medulla are most fully developed at birth
The cerebral cortex is least developed
Medulla regulates vital functions such as heartbeat and respiration, attention, sleeping, waking, elimination, and movement of the head and neck.
The cortex is responsible for perception, body movement, thinking, and language.

3. Major Structures of the Brain
The medulla and the midbrain are largely developed at birth. In the first 2 years after birth, it is primarily the cortex that develops, although the dendrites continue to grow and synapses continue to form throughout the nervous system. The prefrontal cortex is the last part of the brain to mature.

4. The Brain and Nervous System
Growth Spurts: Developmental Timeline
One month intervals until 5 months
Spurts at 8, 12, and 20 months
Middle childhood spurts associated with improved eye-hand coordination and fine motor skills
10–12 year olds have growth in frontal lobes
13–15 year olds have growth in spatial and motor areas
17-year olds have growth in frontal lobes that are associated with logic and planning
Intervals of growth and stability
Correlated with cognitive development

5. Synaptic Development Synaptogenesis Creation of synapses
Rapid occurrence during first years after birth
Brain weight triples by age 2
Happens in spurts
Pruning
Unnecessary pathways and connections are eliminated
Early in development, each muscle cell seems to develop synaptic connections with several motor neurons in the spinal cord. But after the pruning process has occurred, each muscle fiber is connected to only one neuron. Some neurophysiologists have suggested that the initial surge of synapse formation follows a built-in pattern (Greenough et al., 1987). The organism seems to be programmed to create certain kinds of neural connections and does so in abundance, creating redundant pathways. According to this argument, the pruning that takes place beginning at around 18 months is a response to experience, resulting in selective retention of the most efficient pathways.

6. Synaptic Development Both processes heavily dependent on experiences
Follows “use it or lose it” dictum
Early flexibility allows children to adapt to environment better
Programmed plasticity is in its height in infancy
Early in development, each muscle cell seems to develop synaptic connections with several motor neurons in the spinal cord. But after the pruning process has occurred, each muscle fiber is connected to only one neuron. Some neurophysiologists have suggested that the initial surge of synapse formation follows a built-in pattern (Greenough et al., 1987). The organism seems to be programmed to create certain kinds of neural connections and does so in abundance, creating redundant pathways. According to this argument, the pruning that takes place beginning at around 18 months is a response to experience, resulting in selective retention of the most efficient pathways.

7. Myelinization Formation of myelin sheath
Cephalocaudal and proximodistal patterns
Developmental path
Functions
Formation of myelin sheath
Covering around individual axons
Provides insulation and speeds up neuronal processes
Follows cephalocaudal and proximodistal patterns
Most rapid during first 2 years after birth
Continues throughout childhood and adolescence
Helps with selective attention
Ability to focus cognitive activity on the important elements of a problem or situation
Cephalocaudal – head to toe.
Proximodistal – near to far.
Parts of the brain that govern motor growth – 6 years old.
Reticular Formation – keeping attention on what you are doing – continues in spurts until a person is in their mid-20’s.

8. The Neuron
A typical neuron has three major parts: (1) a cell body, which carries out the metabolic functions of the neuron; (2) branched fibers called dendrites, which are the primary receivers of impulses from other neurons; and (3) a slender, tail-like extension called an axon, the transmitting end of the neuron, which ends in many branches, each with an axon terminal. The axon is covered with myelin, a fatty substance that makes the transmission of neural impulses more efficient.

9. Myelinization Helps with selective attention in middle childhood
Associational areas are myelinized by the time children enter school
Hippocampus neurons are also myelinized at this time
Helps in improving long-term memory
Cephalocaudal – head to toe.
Proximodistal – near to far.
Parts of the brain that govern motor growth – 6 years old.
Reticular Formation – keeping attention on what you are doing – continues in spurts until a person is in their mid-20’s.

10. Lateralization Corpus callosum growth and maturation
Left and Right Brain Dominance
Lateralization
Sign language learning
Corpus callosum grows and matures a lot during early childhood
Left and Right Brain Dominance
95% left brain dominant
Some lateralization may be present in fetus
Experience with language is the impetus behind lateralization
Deaf children learning sign language also have brain development

11. Lateralization of Brain Functions
Brain functions are lateralized, as shown in the figure. Neurologists think that the basic outline of lateralization is genetically determined, whereas the specific timing of the lateralization of each function is determined by an interaction of genes and experiences.

12. Lateralization
Spatial Perception: Ability to identify and act on relationships of objects in space
Relative right-left orientation
Most children younger than 8 know the difference between right and left, but may not understand the difference until older than 8

13. Lateralization
Spatial cognition: ability to infer rules from and make predictions about the movements of objects in space
Gender differences
Environmental influences
Boys score higher than girls
May influence boys’ selection of toys and video games that require better spatial cognition, further strengthening that area of the brain

14. Lateralization Handedness Prevalence Incidences Appearance
Prevalence of right-handedness is probably genetic
Dominant gene for right-handedness
96% of right-handers have language processes on the left hemisphere
75% of left-handers are left-brain dominant
1% of left-handers have complete right-brain language
Appears very early in life before the first birthday

15. Bones, Muscles, and Motor Skills
Patterns of Change in Size and Shape: Height and Weight Gains
Phase 1
First 2 years: rapid height gain adding inches
and tripling the body weight in the first year
Phase 2
From 2: adds 2-3 inches and 6 pounds a year until:
adolescence
Phase 3
Adolescent growth spurt
3-6 inches a year for several years
Longer spurts in boys
Height and Weight Gains
Phase 1
First 2 years: rapid height gain adding inches
and tripling the body weight in the first year
Phase 2
From 2: adds 2-3 inches and 6 pounds a year until:
adolescence
Phase 3
Adolescent growth spurt
3-6 inches a year for several years
Longer spurts in boys
Body proportions change with age as well

16. Growth Curve Shifts

17. Bones, Muscles and Motor Skills
Fontanels
Skull soft spots that fuse as bones grow
Filled in by months
Ossification
The process of bone hardening
Occurs steadily from birth to puberty

18. Bones, Muscles, and Motor Skills
Muscles and Fat
Virtually all muscle fibers are present at birth
Developmental changes
Gender differences
Strength
Become longer and thicker
Growth spurt in adolescence
Increase in strength is greater in boys
Adult males: 38% muscle mass
Adult females: 31% muscle mass
Proportions of fat rises in girls and falls in boys

19. Sex Differences in Strength

20. Bones, Muscles, and Motor Skills
Using the Body
Stamina
Changes are linked to growth of the heart and lungs, especially during puberty
Before puberty, boys and girls are similar in physical strength, speed, and stamina
After puberty, boys are ahead in all three
Motor Development
Gross motor skills develop earlier than fine motor skills
Fine motor skills develop rapidly in the elementary school years

21. Stages in Children’s Drawings

22. The Endocrine and Reproductive Systems
Hormones
Pituitary gland
Thyroid and pituitary growth hormones
Adrenal androgen
Gonadatrophic hormones
Pituitary gland: triggers hormone release from other glands
Growth is regulated by thyroid and pituitary growth hormones
Adrenal androgen begins the changes of puberty
Gonadatrophic hormones are secreted to stimulate the testes and ovaries to secrete sex hormones
Testosterone in boys
Estradial in girls

23. The Endocrine and Reproductive Systems
Hormones influence onset of puberty
Primary sex characteristics: development of testes and ovaries
Secondary sex characteristics: breasts in girls; changes in voice and pitch and beard in boys; and body hair for both

24. Sequence of Changes in Girls and Boys
Development of pubic hair and breasts
Growth spurt follows
Menarche follows 2 years after other visible signs
Occurs between 12 ½ and 13 ½
Follows a secular trend—caused by changes in diet and lifestyle
Possible to conceive shortly after menarche, but irregularity is the norm
Menarche follows 2 years after other visible signs
Occurs between 12 ½ and 13 ½
Follows a secular trend—caused by changes in diet and lifestyle
Possible to conceive shortly after menarche, but irregularity is the norm

25. Sequence of Pubertal Changes in Girls
The figure shows the normal sequence and timing of pubertal changes for girls. The red box on each black line represents the average age when the change occurs; the line indicates
the range of normal times. Note the wide range of normality for all of these changes. Also note how relatively late in the sequence the growth spurt and menarche occur.

26. Sequence of Changes in Girls and Boys
Growth spurts come later in the stages than in girls
Development of beard and lowering of voice comes late in the stages
Boys can attain fertility as early as age 12 or as late as age 16
Fertility usually occurs just before a boy reaches his full adult height

27. Sequence of Pubertal Changes in Boys
The sequence of pubertal changes begins about 2 years later for boys than for girls, but as with girls, the height spurt occurs relatively late in the sequence.

28. The Timing of Puberty
Early maturing girls develop an endomorphic body type that is somewhat undesirable
Suffer more negative body image
Get into more trouble in school
Engage in delinquent behavior
Experience more depression
Get into bad peer groups
Abuse substances

29. Timing of Puberty and Body Image
Serious ballet dancers clearly prefer to have a very late puberty. In this study, dancers whose menarche was “on time” by ordinary standards actually had poorer body images than those who were objectively quite late, while the reverse was true for nondancers. Thus, it is perception of timing and not actual timing that is critical.

30. The Timing of Puberty
Early maturing boys develop a mesomorphic body type that is culturally admired
Have positive body image
Does better in school
Get in less trouble and more friends
Can be more hostile and aggressive
Experience stressful life experiences when developing early

31. ? Questions to Ponder Remembering your own adolescence,
Were you an early, normal, or late bloomer?
How did your body changes affect your mental image and your behaviors?
Does the research on sexual behavior match your experiences and that of your friends? Why or why not? ?

32. Sexual Behavior in Adolescence
Prevalence of Sexual Behavior
Gender differences
Multiple partners
High school sexual experience across ethnic groups
High school boys are more sexually active than high school girls
Proportion of teens who have had multiple partners has increased
High school sexual experience varies across ethnic groups
African Americans- 67%
Hispanics- 51%
Whites—42%
African Americans report first sexual encounters before age 13

33. Sexual Experience among High School Students in the United States

34. Explaining Adolescent Sexual Behavior
Social factors are better predictors of sexual activity than hormones
Social Factors
Poor neighborhoods
Less adult monitoring
More likely to use alcohol
Many abused/neglected in early childhood
Early menarche, early dating
Sometimes history of sexual abuse

35. Explaining Adolescent Sexual Behavior
Moral beliefs can lower sexual activity
Sports and after-school activities can lower activity
Teens who do not use alcohol are less likely to be sexually active

36. Sexually Transmitted Diseases and Sex Education
Teens ignorant of STDs
Effective sex education foci
Many teens ignorant of sexually transmitted diseases
90% of teens report learning about STDs in high school
May lack the assertiveness to pressure a partner into safe sex
Chlamydia- most commonly reported
Sex education needs to stress
social and decision-making skills
information about STDs
information about pregnancy

37. Teenage Pregnancy
Higher in United States than in any other Western industrialized country
Ethnic differences
Older adolescent births are more common
Ethnic differences
25% of births to African Americans
17% of births to Hispanics
11% of births to whites
Proportion of teenage mothers who marry the father has declined
Teen pregnancy is lower in girls who do well in school, have strong educational aspirations, and have had good communication about sex education with their mothers

38. Teenage Pregnancy 33% of all teen pregnancies end in abortion
14% result in miscarriage
7% of whites carry the baby to term and give them up for adoption
1% of African American teens give up their babies for adoption
Children of teen mothers are more likely to grow up in poverty
Support programs that help keep teen mothers in school help

39. Homosexuality: Biological Basis Hypothesis
1% of adolescent boys and girls define themselves as male or female homosexual or bisexual
Twin studies show when one identical twin is homosexual the probability the other will be is 50-60%
Family studies suggest male homosexuality runs in families
Such findings strengthen a biological basis hypothesis for homosexuality
1% of adolescent boys and .4% of adolescent girls define themselves as homosexuals. A larger number suggested they were unsure of their sexual orientation. (1994)

40. Homosexuality: Programmed at Birth Hypothesis
Prenatal hormone patterns may be a causal factor in homosexuality
Long bones in arms and legs of homosexual school-age children do not grow as fast as heterosexuals
1% of adolescent boys and .4% of adolescent girls define themselves as homosexuals. A larger number suggested they were unsure of their sexual orientation. (1994)

41. Homosexuality Pattern of realization of homosexuality
May begin in middle childhood
Homosexual fantasies begin in teen years
Full awareness and acceptance appear to take place in early adulthood
Slow process may lead to isolation and peer rejection
1% of adolescent boys and .4% of adolescent girls define themselves as homosexuals. A larger number suggested they were unsure of their sexual orientation. (1994)
Slow process may lead to isolation and feelings of being unaccepted by peers
May lead to depression and attempted suicide
Schools may need to provide emotional and social support for homosexual teens
Homosexual adolescents face similar concerns as other teens in developing identity

42. Health and Wellness Health in Childhood Health Care Needs
Illnesses and Accidents
Age and Gender Differences
Health Care Needs
Periodic medical check-ups
Undiagnosed health issues
10-20% have sleep difficulties
Affects attention, concentration, and causes behavioral problems
Illnesses and Accidents
4-6 brief bouts of sickness each year
Family upheaval can increase levels of sickness
1/4th of children under 5 have at least one accident per year
More common in boys
80% of bicycle-related head injuries involve children

43. Health and Wellness Nutrition Children may eat less Rarely overweight
Acquire eating habits at this time; food aversions
Become more open to new foods during the school years
Obesity
Incidence may be increasing
Body Mass Index (BMI)
For children, use BMI-for-age
The older children get, the more likely they are to remain obese

44. Health and Wellness Dieting Fearful of developing menarche
Knowledgeable about weight loss in school age children
Some begin dieting as early as 7

45. Prevalence of Overweight Children and Teens
The percentages of children and teens who are overweight have increased dramatically over the past five decades.

46. poverty repeats itself
Poverty and Health
Poor children miss more days of school
The cycle of poverty
poor health
low achievement
poverty repeats itself

47. Health and Wellness Adolescent Health Health Care Issues
May develop physical symptoms to parental or peer rejection
Most likely to need medical care for accidents

48. Health and Wellness Adolescent Health Sensation-Seeking
Desire to experience high levels of arousal
Increased rates of accidents
Risky behaviors help teenagers gain peer acceptance and establish autonomy

49. Health and Wellness Alcohol and Drug Use
More common in sensation-seekers
Peers who drink or use drugs seek out others who do the same
Parental perceptions influence abstinence from drugs and alcohol
Parents need to take a proactive approach to prevention

50. Illicit Drug Use Trends among Teenagers
This figure shows the percentage of teens who admitted to using illicit drugs in the previous 12 months. As you can see, drug use rates have declined since the 1970s.

51. Health and Wellness Smoking 12% of adolescents are regular smokers
30% have tried smoking
Teenagers already in poor health are likely to smoke

52. Health and Wellness Smoking Peer influences are strong
Parental influence, especially for mothers and daughters, is important
Parents who resist smoking tend to have non-smoking adolescents

53. Health and Wellness Mortality Worldwide incidence
Causes
United States incidence
Ethnic causes
10% of children worldwide die before age 5
Diarrhea and malnutrition in poor countries
Accidents- especially vehicular accidents in the United States
Childhood deaths are declining in the United States
African American boys in childhood and adolescence have the highest death rate
After age 13, homicide is the leading cause of death in African Americans

54. A Good Night’s Sleep for Kids (and Parents, Too!)
In your opinion, to what extent are parental concerns about where children sleep driven by cultural beliefs and standards of behavior?
What steps can parents take to minimize bedtime conflicts?
Every night Luis and Ramona go through the same ordeal when they put their 3-year-old son, Manny, to bed. The boy begs to sleep with them, but they always refuse. After four or five cycles of begging and sobbing, Manny finally becomes so exhausted that he can no longer stay awake. But the battle doesn’t end at that point. Manny wakes up every night around 2:00 a.m. and slips into his parents’ bed. Usually, Luis and Ramona are sleeping so soundly that Manny’s late-night invasion goes unnoticed, and they awaken to find him in their bed the next morning.
Manny’s nighttime behavior is all too familiar to many parents of preschoolers. Here are the bedtime strategies that most health-care professionals recommend:
• Provide the child with a structured, predictable daytime schedule, and stick to it as closely as possible every day.
• Set a regular bedtime that is 8 to 10 hours before the desired waking time.
• Discontinue daytime naps for a child who has difficulty getting to sleep or who awakens too early in the morning.
• Establish a routine set of “settling activities,” such as a bath, story book, and goodnight kiss, and resist the child’s efforts to prolong or modify the routine.
• Provide the child with a transitional object such as a doll or stuffed animal that is reserved especially for bedtime.
Making such adjustments can be challenging. However, research confirms that these kinds of changes can significantly reduce sleep-related conflicts (Borkowski, Hunter, & Johnson, 2001). Thus, a few days or even weeks of persistence on the parents’ part may pay off in years of undisturbed sleep for parents and children alike.