Human Growth
and
Development
Chapter Five
First Two Years:
Biosocial Development
PowerPoints prepared by Cathie Robertson, Grossmont College
Revised by Jenni Fauchier, Metropolitan Community College
Body Changes
• Rapid changes
• Consequences of neglect severe
Body Size
• Most notable time for physical changes
– in each of the first 12 months they
grow an inch
– birth weight usually doubles by 4
months and triples by end of first
year
– head-sparing—biological protection of
the brain when malnutrition
temporarily affects body growth
Sleep
• Newborns sleep about 17 hours per day
– needed for rapid growth
– REM sleep—rapid eye movement
sleep—declines
– quiet sleep increases at about 3
months
– too immature to sleep through the
night
• Infant’s sleep patterns influenced by
brain waves and parents’ caregiving
practices
Early Brain Development
• Most critical biosocial aspect of growth
– newborn’s skull disproportionately
large
– at birth, 25% of adult brain weight
– by age 2, 75% of adult brain weight
Connections in the Brain
• Head measurement increases 35% in
first year
– brain development: changes in the
brain’s communication system
Basic Brain Structures
• Neurons—long thin nerve cells that
make up nervous system
- created before birth
- 70% in cortex (brain’s outer
layer)
• Axons—nerve fibers that extend
from neurons that send impulses
• Dendrites—nerve fibers extending
from neurons that receive impulses
Areas of the Cortex
Basic Brain Structures, cont.
• Neurons—long thin nerve cells that
make up nervous system
-created before birth
-70% in cortex (brain’s outer
layer)
• Axons—nerve fibers that extend
from neurons that send impulses
• Dendrites—nerve fibers extending
from neurons that receive impulses
Basic Brain Structures, cont.
• Each neuron has a single axon (nerve fiber)
that extends from it and meets the dendrites
of other neurons at intersections called
synapses
- axons and dendrites don’t actually touch at
synapses
- electrical impulses trigger brain chemicals
called neurotransmitters, which carry
information from axon of sending neuron across
synaptic gap to dendrites of receiving neuron
- synapses are critical communication links with
the brain
Connections in the Brain
Exuberance
• At birth more than 100 million
neurons are present
• Phenomenal growth is referred to
as transient exuberance—
fivefold increase in dendrites in
first 2 years
• As many as 15,000 connections
may be made per neuron
Experience Enhances
the Brain
• Specifics of brain structure and
growth depend partly on experience
– exuberance is transient—
transitional stage between newborn
brain’s immaturity and the maturity
of older child’s or adult’s brain
– underused neurons are inactivated,
or pruned
Experience Enhances the Brain,
cont.
• Reactions to Stress
– experiencing stress may cause
overproduction of stress hormone
• developing brain can lose capacity
to react normally to stress
• normal neuron connections may
have been pruned for rapid
response to repeated stress
Experience Enhances the Brain,
cont.
• William Greenough identified 2
experience-related parts of brain growth
– experience-expectant brain functions
• require basic common experiences
to develop normally
– experience-dependent brain functions
• depend on particular and variable
experiences to develop
Experience Enhances the Brain,
cont.
• Human brains are designed for expected
experiences
– how the brain is structured and connected will
depend on those experiences
– the brain expects certain experiences at
certain ages
• these experiences critical if connections
are to form; if connections not formed,
plasticity may allow new connections and
pathways as experiences continue
The Senses and
Motor Skills
• Sensorimotor Stage
– cognition develops between senses
and motor skills
Sensation and Perception
• All senses function at birth
– sensation—the response of sensory
system when it detects stimulus
• begins with outer organ—nose,
eyes, etc.
– perception—mental procession of
sensory information when brain
interprets sensation
• begins in the brain and requires
experience
– cognition—thinking about what was
perceived
Listening
• Begins prenatally and is acute at
birth
• Certain sounds trigger newborns’
reflexes
• Newborns particularly attentive
to human voice
• Newborns’ sensitive hearing
combines with brain to distinguish
sounds
Looking
• Vision the least mature sense at birth
• Visual experience combined with visual
cortex maturation improves vision
- with time scanning becomes more
organized, efficient, and centered
• Binocular vision—ability to focus two
eyes in a coordinated manner to see
single image
Tasting, Smelling,
and Touching
• taste—functions at birth; calmed by
sugar, sensitive to sour
• touch—comforted by human touch; feel
pain
• smell—can distinguish between odors
and have preferences
• Early sensation is organized for
– social interaction
– comfort
Motor Skills
• Most visible and dramatic body change
of infancy
Reflexes
Reflexes for survival are categorized
- maintain oxygen supply (breathing)
- maintain body temperature (crying,
kicking)
- manage feeding (rooting and sucking)
- swallowing aids feeding
- spitting up if too much has been
swallowed
- crying when stomach empty
Gross Motor Skills
• Involve large muscles and body
movements
– crawling, creeping, walking
Fine Motor Skills
• Small, finely tuned movements,
especially of hands and fingers, including
– successful grabbing
– fingering, pointing, and holding
– grasping a moving object
– transferring objects from hand to
hand
– adjusting reach
Age Norms (in Months) for
Gross Motor Skills*
Variations and Ethnic
Differences
• Age at which motor skills acquired
varies greatly because of
– ethnicity
– inherited factors—genetic
differences
– patterns of infant care
– individual rate of physical maturation
Public Health Measures
• Newborn Care
• Immunizations
• Nutrition
Immunization
• Immunization—process that stimulates
body’s immune system to defend against
attack by a particular contagious
disease
– smallpox
– polio
– measles
Sudden Infant Death
Syndrome (SIDS)
• Risk factors?
– laying baby on stomach to sleep
– secondhand smoke
– low birthweight
– formula feeding rather than breast
feeding
Ethnicity and SIDS
• Asian babies less likely to succumb
• Babies of African descent more likely
• Infantcare routines in different
cultures play a role
Nutrition
• How Infants Are Fed
Breast Is Best
• Breast Milk
- begins with colostrum, high-calorie
nourishment before milk “lets down”
- easily digestible
- has antibodies and antibacterial properties
- better for baby’s health
• Bottle Feeding: babies more likely to have
allergies
- better option if mother is HIV-positive or
using drugs
• Feeding on Demand
Malnutrition
• Severe Malnutrition
– brain does not have enough nutrition
to develop normally
– no body reserves to protect from
disease
– marasmus and kwashiorkor diseases
are direct result of malnutrition