Learning Objectives • How is development of the endocrine system involved in growth across the lifespan? • How do the brain and the nervous system develop across the lifespan? • What are milestones in the development of the brain?
Building Blocks of Growth and Development • Human growth is influenced by the interaction of genetic and environmental factors • Inherit a genetic propensity for height (tall, short, medium), but the propensity is affected by environmental influence of nutrition (adequate or inadequate)
Building Blocks of Growth and Development – The Endocrine System • Endocrine glands secrete hormones directly into the bloodstream • Pituitary gland is the master endocrine gland and triggers the release of hormones from all other endocrine glands • Pituitary produces growth hormone • Thyroid gland influences physical growth and development of the central nervous system • Thyroid deficiency can affect intellectual development and growth
Building Blocks of Growth and Development – The Endocrine System • Androgens (including testosterone) • Influence the growth spurt, responsible for development of male sex organs, contribute to sexual motivation • Estrogen • Influences the growth spurt, responsible for development of breasts, pubic hair, and female sex organs, controls the menstrual cycle • Progesterone – the “pregnancy hormone” • Orchestrates changes that allow conception and then supports pregnancy • Adrenal glands secrete androgen-like hormones • Contribute to the maturation of bone and muscle and to sexual motivation
Building Blocks of Growth and Development – The Nervous System • Nervous system consists of the brain and spinal cord (central nervous system or CNS) and the body-wide neural tissue (peripheral nervous system) • Basic unit is the neuron • Neurons have branching dendrites that receive signals from other neurons and a long axon that transmits electric signals to other neurons (or a muscle cell) • Neuron-to-neuron connections are made at a synapse • Axons are covered in myelin, a fatty sheath • Myelination begins prenatally and continues for many years • Progressive myelination is responsible for aspects of development such as language, abstract thinking, concentration, and integration of thought and emotion
Caption: Parts of a neuron. (a) Although neurons differ in size and function, they all contain three main parts: the dendrites, which receive messages from adjacent neurons; the cell body; and the axon, which sends messages across the synapse to other neurons. (b) The formation of dendrites leading to new connections among existing neurons, as well as the myelination of neural pathways, accounts for much of the increase in brain weight during a baby’s first two years.
Building Blocks of Growth and Development – Brain Development • Milestones of brain development • At birth, the brain weighs 25% of its adult weight • By age 2, the brain weighs 75% of its adult weight • By age 5, the brain weighs 90% of its adult weight • During early development, the brain has great plasticity, or responsiveness to experience • Can be highly vulnerable to damage by teratogens • Can often recover successfully from injuries • The critical or sensitive period for brain development is during the late prenatal period and early infancy
Learning Objectives • What is lateralization? How does it affect behavior • How does the brain change with aging? • What principles underlie growth? • What are examples of each principle? • How can we apply a lifespan developmental approach to our understanding of health?
Brain Development • Lateralization in brain development • The functions controlled by the two hemispheres diverge • Typically, the left cerebral hemisphere controls the right side of the body • Adept at the sequential processing needed for analytic reasoning and language processing; “thinking side” of the brain • Typically, the right hemisphere controls the left side of the body • Skilled at the simultaneous processing needed for understanding spatial information and for processing visual-motor information and the emotional content of information; the “emotional side” of the brain • The hemispheres are connected by the neurons that make up the corpus callosum • Signs of lateralization are evident at birth • Direction the head is turned, grasp reflex, hemispheric response to speech sounds
Brain Development • Brain development is never complete • Evidence from research suggests that the brain is responsive to experience and capable of neurogenesis across the lifespan • Process of generating new neurons
Brain Development • As a result of gradual and relatively mild degeneration within the nervous system, the aging brain typically processes information more slowly than does a younger brain • Some loss of neurons, diminished functioning of neurons, and changes to related tissues, such as myelin • Greatest loss in the areas that control sensory and motor activities • Decrease in brain weight and volume • Transmission of signals by atrophied neurons is less effective • Declines in levels of neurotransmitters • Formation of “senile plaques” • Reduced blood flow to the brain
Brain Development • Plasticity and growth make up for degeneration in the brain until people are in their 70s and 80s • A key to maintaining or improving performance in old age is to avoid the many diseases that can interfere with nervous system functioning • Another key is to remain intellectually active
Building Blocks of Growth and Development - Principles of Growth • Three principles that underlie growth • Cephalocaudal principle • Head-to-tail direction • Proximodistal principle • From the center outward to the extremities • Orthogenic principle • Development starts globally and undifferentiated and proceeds toward hierarchal integration and differentiation
Building Blocks of Growth and Development - A Lifespan Developmental Model of Health • Health is a lifelong process • Health is determined by both genetic and environmental influences • Health is multidimensional • Includes physical, mental, and social well-being, not merely the absence of disease or infirmity • Changes in health involve both gains and losses • Health occurs in a sociohistorical context • Socioeconomic status is particularly important
Learning Objectives • What is the typical pattern of growth during the first year of life? • What is the difference between survival and primitive reflexes? What are examples of each type of reflex? • What other capabilities do newborns have? • How do locomotion and manipulation of objects evolve during infancy? • What factors influence the development of infant’s’ motor skills? • What health issues should be considered during the first two years of life?
The Infant – Rapid Growth • Newborns typically weigh 7 to 7½ pounds and are about 20 inches long • By age 2, are about half their eventual adult height and weigh 27-30 pounds on average • Growth occurs in fits and starts and often is accompanied by irritability • Infants whose overall weight gain outpaces gains in height are at risk of childhood obesity
The Infant – Newborn Capabilities • Reflexes are unlearned, involuntary responses to stimuli • Survival reflexes are adaptive • Examples: breathing, eye-blink, sucking • Primitive reflexes are less adaptive and typically disappear in early infancy • Examples: Babinski reflex, grasping reflex • Persistence of primitive reflexes can suggest neurological problems
The Infant – Behavioral States • Organized and individualized patterns of daily activity that suggest the baby is integrating biological, physiological, and psychosocial functions • Initial short sleep-wake cycles become more predictable and stable between 3-6 months • Rapid eye movement (REM) sleep • Newborns spend 50% of their sleep in REM • Infants older than 6 months spend 25-30% of their sleep in REM • May be useful for regulating sensory stimulation
The Infant – Locomotor Development • Developmental norms • Average age of mastery • Early motor development follows the cephalocaudal and proximodistal principles • Can sit before they can walk • The trunk is controlled before the arms and legs • Gross motor skills are mastered before fine motor skills
The Infant – Locomotor Development • Early motor development also demonstrates the orthogenetic principle • An infant will make a global response before a differentiated response • Crawling may take many forms or may not occur • Walking – a major milestone of about 1 year • A more mature nervous system, more muscle, and a less top-heavy stature are necessary for walking
The Infant – Grasping and Reaching • Progression from reflexive response to more voluntary, coordinated behavior • Infants use an ulnar grasp with palm and fingers pressed together • Between 6 and 12 months, reaching and grasping become more proficient • Adjusted to the characteristics of an object • Pincer grasp is reliable by one year of age • Thumb and forefinger
The Infant – Motor Skills as Dynamic Action Systems • Rhythmic stereotypies are performed before a new motor skill emerges • Repetitive movements such as rocking, swaying, bouncing, mouthing objects, banging arms up and down • Dynamic systems theory explains motor developments • A “self-organizing” process in which children use the sensory feedback they receive when they try different movements to modify their motor behavior in adaptive ways
The Infant – Motor Skills as Dynamic Action Systems • According to dynamic systems theory, when children learn to walk • The learning takes into account their biomechanical properties and the characteristics of the environment they must navigate • Nature (the child’s central nervous system) and nurture (sensory and motor experiences) are essential and integral • Action and thought are integrated
The Infant – Health and Wellness • Typical health issues of infancy • Health problems associated with prematurity and low birth weight may persist • Complications of prematurity are second leading cause of death; 1/3 of infant deaths • Congenital malformations, including heart defects, spina bifida, Down syndrome, cleft palate, etc. are leading cause of death
The Infant – Health and Wellness • Infant health has been dramatically improved by the administration of vaccinations against diphtheria, pertussis, polio, and measles • Socioeconomic status is a determinant of access to healthcare and vaccinations • Postnatal health is enhanced by well-baby healthcare to ensure that development is proceeding normally and by following recommendations for prevention of illness
Learning Objectives • What are the typical patterns of growth and physical development in childhood? • What factors influence children’s health? • How can health be optimized during childhood?
The Child – Steady Growth • From age 2 until puberty, children gain 2-3 inches in height and 5-6 pounds annually • Cephalocaudal and proximodistal principles of growth continue to prevail
The Child – Physical Behavior • Children learn to move capably in a changing environment • By age 3, walk or run in a straight line • By age 4, perform a different activity with each hand • Kindergartners can integrate motor skills into a higher-level skill • Motor skills are responsive to practice • Boys are more skilled in throwing and kicking • Girls are more skilled in hopping and in manual dexterity
The Child – Physical Behavior • From age 3 to age 5, eye-hand coordination and control of small muscles improve • By age 8 or 9, children can use tools such as a screwdriver and are skilled at games requiring eye-hand coordination • Reaction time improves steadily throughout childhood
The Child – Health and Wellness • Parents’ education and socioeconomic status are factors that influence children’s health • Accidents are the leading cause of death during childhood • Motor vehicle crashes cause the most fatal injuries • Nutrition continues to contribute to health • Children need a well-balanced diet, but societal influences inadvertently encourage poor eating habits
Caption: Among white and black families, parent’s education level influences the extent to which children’s activities are limited by poor or fair health. Children have more limitations when their parents are less educated. This is not true among Hispanic and Asian families.
The Child – Health and Wellness: Nutrition • Parents can influence children’s nutrition by offering healthy foods and modeling healthy eating habits • Schools influence children’s eating habits and health • Breakfast programs • School lunches often have higher than recommended levels of fat and sodium and lower than recommended levels of fiber
The Child – Health and Wellness: Nutrition • Regular physical activity fosters health during childhood • Children should have at least 60 minutes of moderate or vigorous physical activity daily • The average child spends 5-6 hours in sedentary activities each day • Obesity rates have tripled over the past 30 years and are especially high among ethnic minority children • Obesity – being 20% or more above the ideal weight for one’s height, age, and sex
Caption: Increase in childhood/teen obesity rates over a 30-year period (1976-2006)
Learning Objectives • What physical changes occur during adolescence? • What factors contribute to sexual maturity of males and females? • What psychological reactions accompany variations in growth spurt and the timing of puberty?
The Adolescent – The Growth Spurt • The growth spurt is triggered by an increase in the level of growth hormones • Girls’ peak rates of growth • For height – not quite 12 years of age • For weight – 12.5 years • Boys’ peak rates of growth • For height – 13.4 years of age • For weight – 13.9 years • Girls achieve adult height around 16; boys continue to grow until 18, 19, or 20
The Adolescent – Sexual Maturation • Increased production of adrenal androgens (adrenarche) contributes to secondary sex characteristic of pubic/axillary hair • Increased production of gonadal hormones primarily responsible for secondary sex characteristics and sexual maturation • “Tanner Scale” used to measure progression through five stages of sexual maturity • Menarche is the most dramatic event in girls’ sexual maturation process
The Adolescent – Sexual Maturation • Girls’ sexual maturation is influenced by ethnicity, weight at birth, and weight gain during childhood • The lighter a girl is at birth and the more weight she gains during childhood, the earlier she begins menstruating • Boys’ sexual maturation process begins at age 11-11½ with growth of testes and scrotum • The marker of sexual maturation for boys is semenarche, first emission of seminal fluid, around age 13
The Adolescent – Sexual Maturation • The rate of development during adolescence is determined by • Genes that trigger production of hormones • Environment • The secular trend • The historical trend in industrialized societies toward earlier maturation and greater body size (caused by improved nutrition and advances in medical care) • For girls, family situation • Presence of an unrelated male in the household, family disruption, harsh mothering
Sexual Maturation – Psychological Implications • Girls become concerned with appearance and worry about the responses of others • Individual reactions vary widely • May develop negative views about menstruation and poor body images as a result of weight gain • Boys are likely to welcome weight gain and voice changes and to react positively to semenarche
Sexual Maturation – Psychological Implications • Puberty typically prompts changes in family relations • Physical distancing is typical • Teens may become more independent and less close to parents • Conflict is likely but about minor issues • Family relations will be influenced by cultural beliefs about the significance of becoming an adult • Parents can facilitate the adjustment to puberty by maintaining close relationships and helping adolescents accept themselves
Sexual Maturation – Early versus Late Development • Early development for boys • Advantages – judged to be socially competent, attractive, and self-assured • Disadvantages – increased risk of earlier involvement in substance use and problem behaviors such as bullying, delinquency • Late maturation in boys • More negative effects – more anxious, less sure of themselves, more behavior and adjustment problems, lower achievement test scores • Positive effect – less likely to use alcohol
Sexual Maturation – Early versus Late Development • Early development for females • More disadvantageous – subject of ridicule; higher level of body dissatisfaction • Socialization with older peer group can lead to dating, substance use, sexual activity. • Girls who experience early puberty and early sex report higher levels of depression • Late development for females • Advantage – good school performance • Disadvantage – some anxiety
Sexual Maturation – Early versus Late Development • Late-maturing boys and early-maturing girls are especially likely to find adolescence to be disruptive • Differences between early and late developers tend to fade with time • Effects of timing of puberty depend upon the adolescent’s perception of whether puberty events are experienced early, on time, or late • Reactions of peers and family members to an adolescent’s pubertal changes are instrumental in determining the adolescent’s adjustment
The Adolescent – Physical Behavior • Dramatic physical growth makes teens more physically competent, stronger, than children • Adolescents are less physically active than they should be - Girls are more sedentary than boys • Gender-role socialization may be partly responsible • The male-female gap in physical performance among top athletes has narrowed