Physical Development in Infancy

Growth and Stability

Physical Growth: The Rapid Advances of Infancy

• Infants grow at a rapid pace over the first 2 years of their lives
  • 5 months: average birthweight doubles to around 15 pounds
  • 1 year: weight triples to about 22 pounds
  • End of 2nd Year: average child weighs around 4 times as much as she or he did at birth
• not all parts of an infant’s body grow at the same rate
  • Birth: head accounts for 1/4 of the newborn’s entire body size
  • During First and Second Year: rest of the body begins to catch up
• there are gender and ethnic differences in infant weight and length

4 Principles of Growth

• Cephalocaudal Principle
  • the principle that growth follows a pattern that begins with the head and upper body parts and then proceeds down to the rest of the body
  • means that we develop visual abilities (located in the head) well before we master the ability to walk (closer to the end of the body)
• Proximodistal Principle
  • the principle that development proceeds from the center of the body outward
  • means that the trunk of the body grows before the extremities of the arms and legs
  • development of the ability to use various parts of the body
  • effective use of the arms precedes the ability to use the hands
• Principle of Hierarchical Integration
  • the principle that simple skills typically develop separately and independently but are later integrated into more complex skills
  • the relatively complex skill of grasping something in the hand cannot be mastered until the developing infant learns how to control -- and integrate -- the movements of the individual fingers
• Principle of the Independence of Systems
  • the principle that different body systems grow at different rates
  • Birth: around 7 pounds; 20 inches
  • 5 Months: doubled birthweight
  • 12 Months: tripled birthweight; 30 inches
  • 2 Years: slows; 4 times birthweight; 36 inches

The Nervous System and Brain: The Foundations of Development

Elements of the Nervous System

• Neurons: the basic nerve cell of the nervous system
• Dendrites: clusters of fibers, receive messages from other cells
• Axon: the part of the neuron that carries messages destined for other neurons
• Neurotransmitters: travel across the small gaps
• Synapses: the gap at the connection between neurons, through which neurons chemically communicate with one another
• Organization
  • neurons are the basic cells of the nervous system
  • nervous system comprises the brain and the nerves that extend throughout the body
• Birth
  • 100-200 billion neurons
  • relatively few connections
• During the first 2 years
  • billions of connections established

Use it or Lose it!

• babies are born with many more neurons than they need
  • although synapses are formed throughout life, based on our changing experiences, the billions of new synapses infants form during the first 2 years are more numerous than necessary
• Synaptic Pruning
  • unused neurons are eliminated
  • allows established neurons to build more elaborate communication networks with other neurons
  • development of nervous system proceeds most effectively through loss of cells
  • the elimination of neurons as the result of nonuse of lack of stimulation
• Myelinization
  • axons receive “insulation” to speed neural conduction
  • Myelin: a fatty substance that helps insulate neurons and speeds the transmission of nerve impulses

Form and Function: Brain Growth

• neurons reposition themselves with growth, becoming arranged by function
  • Cerebral Cortex: upper layer of the brain
  • Subcortical Levels: below the cerebral cortex
• the ^^cerebral cortex^^, which are responsible for higher-order processes such as thinking and reasoning, become more developed and interconnected
• the ^^subcortical levels^^, which regulate such fundamental activities as breathing and heart rate, are the most fully developed at birth

Shaken Baby Syndrome

• brain sensitive to forms of injury
• shaking can lead to brain rotation within skill
  • blood vessels tear, leading to severe medical problems, long-term disabilities, and sometimes death
• can lead to extreme death and paralysis
• DAI: injury to the brain

Environmental Influences on Brain Development

• Plasticity: the developing brain’s structure and function can be modified due to experience
• Sensory Experiences: an infant’s interactions with the world can influence the size of individual neurons and the structure of their interconnections
• Sensitive Period: a specific, limited time during which an organism is susceptible to environmental influences on a particular aspect of development

Integrating the Bodily Systems: The Life Cycles of Infancy

Rhythms and States

• Rhythms
  • repetitive, cyclical patterns of behavior
  • sleep, wakefulness, eating, elimination
• States
  • degree of awareness an infant displays to both internal and external stimulation
  • change in state alters the amount of stimulation required to get an infant’s attention
  • electrical brain waves can be measured by electroencephalogram (EEG)

Primary Behavioral States

• Awake States
  • Alert: attentive or scanning, the infant’s eyes are open, bright, and shining (6.7%)
  • Non-Alert Waking: eyes are usually open but dull and unfocused; varied but typically high motor activity (2.8%)
  • Fuss: fussing is continuous or intermittent, at low levels (1.8%)
  • Cry: intense vocalization occurring singly or in succession (1.7%)
• Transition States between Sleep and Waking
  • Drowse: infant’s eyes are heavy-lidded but opening and closing slowly; low level of motor activity (4.4%)
  • Daze: open but glassy and immobile eyes; state occurs between episodes of alert and drowse; low level of activity (1.0%)
  • Sleep-Wake Transition: behaviors of both wakefulness and sleep are evident; generalized motor activity; eyes may be closed or they open and close rapidly, state occurs when baby is awakening (1.3%)
• Sleep States
  • Active Sleep: eyes closed; uneven respiration; intermittent rapid eye movements; other behaviors (smiles, frowns, grimaces, mouthing, sucking, sighs, and sigh-sobs) (50.3%)
  • Quiet Sleep: eyes are closed and respiration is slow and regular; motor activity limited to occasional startles, sigh-sobs, or rhythmic breathing (28.1%)
• Transitional Sleep States
  • Active-Quiet Transitional Sleep: during the state, which occurs, between periods of active sleep and quiet sleep, the eyes are closed and there is little motor activity; infant shows mixed behavioral signs of active sleep and quiet sleep (1.9%)

Sleep: Perchance to Dream?

• Major State: 16 to 17 hours daily (average); wide variations
• Different than Adult Sleep
  • 2-hour spurts; periods of wakefulness
  • cyclic pattern
  • by week 16, sleep about 6 continuous hours, by 1 year sleep through the night

REM Sleep

• Rapid Eye Movement (REM)
  • period of sleep that is found in older children and adults and is associated with dreaming
  • period of active sleep
  • closed eyes begin to move in a back-and-forth pattern
  • takes up approximately 1/2 of infant sleep
  • may provide means for brain to stimulate itself through autostimulation
• not easy to wake them up as they are in deep sleep
• spend time in REM stage as they need their brain to grow

SIDS: The Unanticipated Killer

• Sudden Infant Death Syndrome (SIDS)
  • unexplained death of a seemingly healthy baby
  • a disorder in which seemingly healthy infants die in their sleep
  • strikes about 1 in 2500 infants in the US each year
  • although it seems to occur when normal patterns of breathing during sleep are interrupted, researchers have been unable to discover why that might happen
• difficulty in breathing; sudden (rare cases); might be birth defects or something that happens in the brain
• accidental suffocation

Motor Development

• shape and proportions of newborns are simply not conducive to easy mobility
• young infants lack the strength to raise large heads
• movement is further impeded because limbs are short in relation to the rest of the body
• infant babies are mainly fat, with a limited amount of muscle, the result is a lack of strength

BUT

• newborns have an extensive repertoire of behavioral possibilities brought about by innate reflexes, and their range of motor skills grows rapidly during the first 2 years of life
• Fine Development: motor development that use minimal amount of muscles (hands, hand gestures)
• Gross Development: more muscles or bigger category of muscles that helps the baby to move
• they do hand in hand in terms of motor development

Some Basic Reflexes in Infants

• Rooting Reflex (3 weeks)
  • neonate’s tendency to turn its head toward things that touch its check
  • Possible Function: ^^food intake^^
• Stepping Reflex (2 months)
  • movement of legs when held upright with feet touching the floor
  • Possible Function: ^^prepares infants for independent locomotion^^
• Swimming Reflex (4-6 months)
  • infant’s tendency to paddle and kick in a sort of swimming motion when lying face down in a body of water
  • Possible Function: ^^avoidance of danger^^
• Moro Reflex (6 months)
  • Activated when support for the neck and head is suddenly removed. The arms of the infant are thrust outward and then appear to grasp onto something.
  • Possible Function: ^^similar to primates’ protection from falling^^
• Babinski Reflex (8-12 months)
  • an infant fans out its behaviors in response to a stroke on the outside of its foot
  • Possible Function: ^^unknown^^
• Startle Reflex (remains in different form)
  • an infant, in response to a sudden noise, flings out its arms, arches its back, and spreads its fingers
  • Possible Function: ^^protection^^
• Eye-Blink Reflex (remains)
  • rapid shutting and opening of eye on exposure to direct light
  • Possible Function: ^^protection of eye from direct light^^
• Sucking Reflex (remains)
  • infant’s tendency to such at things that touch its lips
  • Possible Function: ^^food intake^^
• Gag Reflex (remains)
  • an infant’s reflex to clear its throat
  • Possible Function: ^^prevents choking^^
• Premature Baby: have to feed separately; limit the amount of milk in the body (they easily throw up)
• Burp: to help with digestion

Ethnic and Cultural Differences and Similarities in Reflexes

• Reflexes
  • genetically determined
  • universal
• Cultural Variations in Ways Displayed
  • Moro reflex
• Functions
  • diagnostic tool
  • social function
  • survival function
• reflexes are used for survival
• Girls: develop verbal early; Boys: faster in motor development
• If child has learning disability: they have a delay in motor development

Motor Development in Infancy: Landmarks of Physical Achievement

Gross Motor Skills: Milestones of Motor Development

Dynamic Systems Theory: How Motor Development is Coordinated

• Dynamic Systems Theory
  • a theory of how motor skills develop and are coordinated
  • describes how motor behaviors are assembled
  • motor skills do not develop in a vacuum
  • each skill advances in the context of other motor abilities
  • as motor skills develop, so do non-motoric skills
  • theory places emphasis on child’s own motivation (a cognitive state) in advancing important aspects of motor development
• body coordination is challenging

Developmental Norms: Comparing the Individual to the Group

• Norm: the average performance of a large sample of children of a given age
• comparing individuals to group norms
  • represent the average performance of a large sample of children of a given age
  • permit comparisons between a particular child’s performance on a particular behavior and the average performance of the children in the normative group
  • must be interpreted with caution
• Brazelton Neonatal Assessment Scale (NBAS)
  • one of the most widely used techniques to determine infants’ normative standing
  • measure designed to determine infants’ neurological and behavioral responses to their environment
  • provides a supplement to the traditional Apgar Test

Nutrition in Infancy: Fueling Motor Development

• without proper nutrition, infants cannot reach physical potential and may suffer cognitive and social consequences
• infants differ in growth rates, body composition, metabolism, and activity levels
• breast feed babies have stronger bones
• Least: 3 years but mother can last until 6 years
• if mother is cut from breastfeeding, mother gets sick for 1-2 weeks; natural production of milk will also stop

A Healthy Caloric Allotment for Infants

• about 50 calories per day for each round of weight
• most infants regulate their caloric intake quite effectively on their own
• if infants are allowed to consume as much as they seem to want, and not pressured to eat more, they will be healthy

Malnutrition

• condition of having improper amount and balance of nutrients, produces several results, none good
• more common in children living in developing countries
• slower growth rate
• chronically malnourished during infancy -- lower IQ score later
• hair color is different; look like the hair from corn

When Malnutrition is Severe

• Maramus
  • malnutrition during first year
  • infants stop growing
  • attributable to severe deficiency in proteins and calories
  • causes the body to waste away and ultimately results in death
• Kwashiorkor
  • found in older children
  • child’s stomach, limbs, and face swell
  • body struggles to make use of few available nutrients
• PEM: insufficient intake of protein
• one of the leading causes of death
• Worst: combination of both

Obesity

• clear links between obesity in infancy and obesity later in life have not been established
• appropriate nutrition, rather than weight, should be the focus of parents
• Worse than Malnutrition: if a child is obese, after a few years in the early childhood-adolescence, can get diseases and vices, by age 30, kidney failure if they did not change their lifestyle

Breast or Bottle?

• Breast Milk
  • offers all nutrients infants need for first 12 months of life
  • is more easily digested than alternative sources
  • provides some immunity to a variety of childhood disease
  • may enhance cognitive growth
  • offers significant emotional advantages for mother and child
  • not a cure-all for infant nutrition and health
• if mother cannot get proper nutrients, her body cannot support the baby
• problem with bottle milk, not all milk cannot be digested by baby

Introducing Solid Foods: When and What?

• solids can be started at 6 months but are not needed until 9-12 months (AAFP)
  • introduced gradually, one at a time
  • cereal and strained fruits
• time of weaning varies greatly across developed and developing countries
• Healthiest: fruit crops (potato, carrots; boiled)

The Development of the Senses

Visual Perception: Seeing the World

• Sensation: the physical stimulation of the sense organs
• Perception: the sorting out, interpretation, analysis, and integration of stimuli involving the sense organs and brain
• newborn’s distance vision ranges from 20/200 to 20/600
• by 6 months, average infant’s vision is already 20/20
• other visual abilities grow rapidly
  • Binocular Vision: 2 eyes used; look at single surface
  • Depth Perception: use 1 eye to recognize

Infant Visual Perception

• preferences that are present from birth
  • genetically preprogrammed to prefer particular kinds of stimuli
  • prefer to look at patterned vs simpler stimuli

Facing the World

• genetics is not the sole determinant of infant visual preferences
  • a few hours after birth, infants have already learned to prefer their own mother’s face to other faces
  • similarly, between the ages 6 and 9 months, infants become more adept at distinguishing between the faces of humans, while they become less able to distinguish faces of members other species
  • they also distinguish between male and female faces

Auditory Perception: The World of Sound

• Infants
  • hear before birth and have good auditory perception after they are born
  • are more sensitive to certain frequencies
  • reach adult accuracy in sound localization by age 1
  • can discriminate groups of different sounds
  • react to changes in musical key and rhythm
  • can discriminate many language related words
  • are born with preferences for particular sound combinations which may be shaped by prenatal exposure to mother’s voices

Smell and Taste

• Smell
  • well developed at birth
  • helps in recognition of mother early in life
  • used to distinguish mother’s scent (only in breastfed babies); cannot distinguish father basis of odor
• Taste
  • have innate sweet tooth
  • show facial disgust at bitter taste
  • develop preferences based on what mother ate during pregnancy

Sensitivity to Pain and Touch

Contemporary Views on Infant Pain

• It is widely acknowledged that infants are born with the capacity to experience pain
• developmental progression in reaction to pain
• exposure to pain in infancy may leas to permanent rewiring of nervous system, resulting in greater sensitivity to pain during adulthood
• sensitive to pain and temperature

Power of Touch

• Touch is one of most highly developed sensory systems in a newborn
• even youngest infants respond to gentle touches
• several of the basic reflexes present at birth require touch sensitivity to operate
• lesser touch = developmental health issue overnight

Multimodal Perception: Combining Individual Sensory Inputs

• Multimodal Approach to Perception: the approach that considers how information that is collected by various individual sensory systems is integrated and coordinated
• New Area of Study in Infant Research
  • some researchers argue that sensations are initially integrated with one another in the infant
  • others maintain that infant’s sensory systems are initially separate and that brain development leads to increasing integration
  • it does appear that by an early age infants are able to relate what they have learned about an object through one sensory channel to what they have learned about it through another
• senses are growing, as we mature the more applicable the senses are