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Chapter 5

Chapter 5 Infants and Children 7th Edition

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University of Waterloo
Kathleen Bloom

III: INFANCY AND TODLERHOOD: FIRST 2 YEARS Chapter 5: Physical Development in Infancy and Toddlerhood Changes in Body Size and Muscle-Fat Makeup - Dramatic increase in body size – rather than making steady gains, infants and toddlers grow in little spurts (babies = irritable and very hungry on days before spurts) - Major change = transformation into round, plump baby by middle of first year (“baby fat” heps maintain constant body temperature) o In second year, most toddlers start to slim down o Muscle tissue increases slowly and does not reach peak until adolescence - Girls slightly shorter/lighter than boys, higher ratio of fat to muscle (small sex differences persist throughout early and middle childhood and greatly magnified at adolescence) Changes in Body Proportions - Two growth patterns: o Cephalocaudal trend: “head to tail” – during prenatal period, head develops more rapidly than lower part of body o Proximodistal trend: growth proceeds, literally, from “near to far” – from center of body outward Skeletal Growth - General Skeletal Growth: Best estimate of child’s physical maturity is skeletal age (measure of development of bones of the body) o Embryonic skeleton is first formed out of soft, liable tissue (cartilage) th o 6 week of pregnancy, cartilage cells begin to harden into bone - gradual process continues throughout childhood and adolescence o Just before birth, special growth centers (EPIPHYSES) appear at two extreme ends of long bones of the body – cartilage cells produced at growth plates of epiphyses – increase in number throughout childhood and then, as growth continues, get thinner and disappear o Skeletal age can be estimated by X-raying bones and seeing # of epiphyses and extent to which they are fused - Growth of Skull – skull growth especially rapid b/w birth and 2 years o At birth, bones of skull separated by “soft spots” – FONTANELS (gaps permit bones to overlap as large head of baby passes through mother’s narrow birth canal)  Largest fontanel (anterior fontanel) gradually shrinks, filled up durinyear  Other fontanels smaller, so close more quickly  As skull bones come in contact with one another, form SUTURES (seams) – permit skull to expand easily as brain grows – sutures disappear completely in adolescence when skull growth complete Brain Development - Development of Neurons (nerve cells) – have thousands of direct connections with other neurons, neurons are NOT tightly packed together, they have tiny gaps or SYNAPSES between them where fibers from diff neurons come close together but do not touch – neurons send messages to one another by releasing NEUROTRANSMITTERS which cross the synapse o Prenatal period: neurons produced in embryo’s primitive neural tube o Then migrate to form major parts of brain o Once in place, differentiate and establish unique functions by extending their fibers to form synaptic connections with neighboring cells o Infancy + Toddlerhood: neural fibers and synapses increase at astounding pace  as synapses form, surrounding neurons die (to make space)  as neurons form connections, STIMULATION becomes vital to their survival (those stimulated by input from surrounding environment continue to establish new synapses, form more connections  more abilities  at first, stimulation results in massive overabundance of synapses  Neurons that are seldom stimulated soon lose their synapses (SYNAPTIC PRUNIING – returns neurons not needed at the moment to an uncommited state so they can support future development)  Dramatic increase in brain size during first 2 years  ½ of brain volume made of GLIAL CELLS (responsible for myelination – coating of neural fibers w/ insulating fatty sheath called myelin that improves the efficiency of message transfor)  **gains in neural fibers and myelination - Neurophysiological Methods o Detecting electrical activity in cerebral cortex  EEGs brain-wave patterns - stability + organization – signs of mature cortical fnctioning  ERPs – detect general location of brain-wave activity to study preverbal infants’ responsiveness to particular stimuli – impact of experience on specialization of specific brain regions and atypical brain functioning (ie. risk for learning/emotional problems) o Neuroimaging Techniques (detailed 3D computerized pictures of entire brain and its active areas – most precise information) – require infant to lie down and not move (difficult for children)  PET – child lies down on scanner bed, depends on X-ray photography (injection of radioactive substance)  fMRI – tunnel-like apparatus, does NOT depend on X-ray  when child is exposed to a stimulus, detects change in blood flow nad oxygen metabolism magnetically  Near Infrared Spectroscopy (NIRS) - infrared (invisible) light beamed at regions of cerebral cortex to measure blood flow + oxygen metabolism while child attends to as timulus - thin flexible fibers attached to scalp with head cap (baby can sit on parent’s lap and move during tests – easier)  Limited to examining function of cerebral cortex - Development of the Cerebral Cortex: cerebral cortex surrounds rest of brain, is largest brain structure (85% of weight), greatest number of neurons and synapses, last part of brain to stop growing, sensitive to environmental influences o Regions of the Cortex – order in which cortical regions develop corresponds to order in which various capacities emerge in infant/growing child  Most extended period of development – Frontal Lobes  Prefrontal cortex – lyes in front of areas controlling body movement, responsible for thought (esp. consciousness, inhibition of impulses, integration of information, and use of memory, reasoning, planning, and problem-solving)  Undergoes v. rapid myelination and formation and pruning of synapses during preschool + school years – another period of accelerated growth follows in adolescence o Lateralization and Plasticity of the Cerebral Cortex  2 hemispheres, differ in function  Each hemisphere receives sensory info from OPPOSITE body side and controls only that side  Left hemisphere: verbal abilities and positive emotion  Right hemisphere: spatial abilities + negative emotion  Lateralization occurs because….  Left hemisphere is better at processing info at a sequential, analytical (piece- by-piece) way – good for communicative info (verbal + emotional)  Right hemisphere – processing info in holistic, integrative manner (good for sense of spatial info and regulating negative emotion..)  A lateralized brain may have evolved because enables humans to cope more successfully with changing environmental demands! - two hemispheres communicate and work together **  Brain plasticity: highly plastic cerebral cortex (many areas are not yet committed to specific functions) = high capacity for learning! – if part of cortex is damaged, other parts can take over – research on brain-damaged children offers evidence for substantial plasticity in young brain  once hemisphere lateralizes damage to a specific region means that the abilities it controls cannot be recovered to the same extent or as easily as earlier  early experiences also influence organization of cerebral cortex - Sensitive Periods in Brain Development – early extreme sensory deprivation results in permanent brain damage and loss of function = sensitive periods in brain development (quality of early environment affects overall brain growth) – Some examples: o Babies are born with cataracts in both eyes – those who have corrective surgery w/i 4-6 months show rapid improvement in vision  The longer cataract surgery is postponed beyond infancy, less complete the recovery in visual skills o Orphanages - infants who were later exposed to ordinary family rearing confirm importance of a generally stimulating environment for psychological development  Early lack of stimulation permanently damaged the brain o Early prolonged institutionalization  reduction in brain wave and metabolic activity in cerebral cortex (esp. prefrontal cortex – complex cognition + impulse control) o Chronic stress of early deprived orphanage rearing disrupts brain’s capacity to manage sress  Compared with agemates adopted shortly after birth, those who spent first 8 months in deprived orphanage – high concentrations of stress hormone cortisol in saliva (physiological response linked to illness, retarded physical growth, and learning/behaviour problems)  Disrupt brain’s response to pleasurable social experiences  Abnormally low levels of oxytocin - hormone released that evokes calmness and contentment in presence of familiar trusted people  attachment difficulties o Appropriate Stimulation: loving care (holding gently, speaking softly, breastfeeding) – prevent irreversible damage to brain  Sensitive adult care also normalizes cortisol production  Protects young brain from potentially damaging effects of both excessive and inadequate stress-hormone exposure o In addition to impoverished environments, those that overwhelm child with expectation beyond their current capacities also interfere with brain’s potential – “Superbabies”  Trying to prime infants with stimulation for which they are not ready can cause them to withdraw/ threatens their interest in learning  Therefore… Apropriate stimulation – two types of brain growth  Experience-Expectant Brain Growth: young brain’s rapidly developing organization (depends on ordinary experiences – opportunities to see/touch objects, hear language/other sounds, move about, explore environment) o Occurs early and naturally – provides foundation for later-occurring experience-dependent development  Experience-Dependent Brain Growth: occurs throughout life, additional growth and the refinement of established brain structures as a result of specific learning experiences – vary across individuals and cultures - Changing States of Arousal - sleep and wakefulness changes substantially b/w birth -2years o Total sleep time declines slowly, periods of sleep and wakefulness become fewer and longer o These changes are due to brain development and also affected by social environment o Middle of first year: secretion of melatonin 0 hormone within brain that promotes drowsiness – much greater at night than during the day o Isolating infants to promote sleep is rare elsewhere in the world – when babies sleep with parents and their average sleep period remains constant at 3h from 1-8 months of age – only at end of first year, as REM sleep declines, do infants move toward adult-like sleep-wake schedule Influences of Early Physical Growth - Heredity: “catch-up growth” – a return to a genetically determined growth path (once diet and health are adequate and negative environmental influences are removed) - Nutrition: especially crucial first 2 years since baby’s brain + body growing rapidly o Breastfeeding vs. bottle-feeding: breast milk ideally suited for baby’s needs while bottle formulas try to imitate it  Breastfed babies in poverty-stricken regions much less likely to be malnourished/survive  WHO recommends breastfeeding until age 2 w/ solid food added at 6months  Even breastfeeding for just a few weeks offers some protection against respiratory and intestinal infections – also helps increase spacing among siblings  In place of breast milk, mothers in Africa, Middle East, and Latin America give babies commercial formula or low-grade nutrients  Contamination of these foods due to poor sanitation is common  illness/infant death  Breast feed unless have viral/bacterial infection (ie. HIV/tuberculosis) that can transmit to baby  Reasons to breastfeed: provides correct balance of fat/protein, ensures nutritional completeness, helps healthy physical growth, protects against many diseases, protects against faulty jaw development/tooth decay, ensures digestibility, smoothes transition to solid foods  Breastfed vs bottle-fed infants do not differ in quality of mother-infant relationship/later emotional adjustment… but do show slight advantage in intelligence test performance, but no cognitive benefits o Chubby Babies: at risk for later overweight/obesity?  Most thin out during toddlerhood + preschool years, weight gain slows and they become more active  But there is some evidence of relationship b/w rapid weight gain in infancy and later obesity - rise in overweight/obesity among adults who promote unhealthy eating habits to their young children  How to prevent? – breastfeed for 6 months (associated with slower weight gain) avoid food loaded w/ sugar, salt, and saturated fats, provide opportunities for exercise/play - Malnutrition o Belly enlarged, feet swelled, hair fell out, rash, irritable + listless (some effects) o Developing countries – food resources limited, malnutrition widespread o 2 main dietary diseases that severely affect (malnutrition before age 5)  Marasmus – wasted condition of body caused by diet low in all essential nutrients. st  Usually appears in 1 year of life when baby’s mother is too malnourished to produce enough breast milk and bottle-feeding is also inadequate  Starving baby becomes painfully thin and in danger of dying  Kwashiorkor – caused by unbalanced diet very low in protein – usually striekes after weaning, b/w 1-3 years of age – common in regions where children get just enough calouries from starchy food but little protein, child’s body responds by breaking down its own protein reserves  results in swelling and other symptoms from first point above o Children surviving these often grow to be smaller in body dimensions, suffer from lasting damage to brain, heart, liver, etc o When diets improve, tend to gain excessive weight - malnourished body protects itself by establishing low metabolism rate – endures even after nutrition improves o May also disrupt appetite control centers in brain causing overeating when food becomes plentiful o Learning + behaviour also affected – interferes with growth of neural fibers + myelination = permanent loss in brain weight o More intense stress response to fear-arousing stimuli o Passivity and irritability o Iron-deficiency Anemia – condition common among poverty-stricken infants – interferes with many CNS processes – withdrawal/listlessness reduce ability to pay attention, explore, and evoke sensitive care giving from parents o Interventions – strive to improve family situations + nourishment o Food insecurity – uncertain access to enough food for a healthy, active life - Emotional Well-Being – affection just as vital as food! o Growth faltering: infants whose weight, height, and head circumference are substantially below age-related growth norms and who are withdrawn and apathetic – in many as half such cases a disturbed parent-infant relationship contributes to this failure to grow normally o unhappy marriage/parental psychological disturbances are also examples that contribute Learning Capacities - Learning: changes in behaviour as result of experience – babies come into world with built-in learning capacities – capable of two basic forms of learning as well as through novel stimulation - Classical Conditioning: a neural stimulus is paired with a stimulus that leads to a reflexive response o Once baby’s nervous system makes connection between the two stimuli, the neutral stimulus produces the behaviour by itself o Helps infants recognize which events usually occur together in the everyday world so they can anticipate what is about to happen next – environment = more orderly and predictable o STEPS: unconditioned stimulus (UCS) must consistently produce reflexive or unconditioned response (UCR). Then a neutral stimulus that does not lead
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