Download Infancy: Physical Development

CHAPTER 4
Infancy: Physical Development
Physical Growth and Development
Sequences of Physical Development
Cephalocaudal and Proximodistal
• Cephalocaudal
– Development proceeds from the upper part of the head to the
lower parts of the body
– Due to the importance of brain regulation such as breathing
– Head develops more rapidly than the rest of the body during
embryonic stage
• Proximodistal
– Development proceeds from the trunk outward
– From body’s central axis toward the periphery
– Brain and spinal cord follow a central axis down through body
due to necessity for nerves to be in place before infant can
control arms and legs
Differentiation
• As children mature, physical reactions become
– less global
– more specific
• Neonate’s response
– to stimuli such as a burn may include thrashing about, crying,
withdrawing the burned finger
• Toddler’s response
– may cry as well and withdraw finger, but thrashing about as a
response to the pain is gone
Patterns in Height and Weight
• Most dramatic gains in height and weight occur during
prenatal development
• Weight gains
– 5 months
– 1st year
– 2nd year
Double birth weight
Triple weight
Gain 4 to 7 pounds
• Height gains
– Infants grow in spurts and do not follow smooth growth chart
– 1st year
Height increases by 50%
– 2nd year
Grow 4 to 6 inches:
Fig. 4-1, p. 73
Changes in Body Proportions
• Head
– Neonate head is about one-fourth the length of body
– Gradually diminishes in proportion to the body
– Doubles in size by adulthood
• Arms and legs
–
–
–
–
Equal in length in the neonate
Arms grow more rapidly than the legs at first
Arms grow longer than legs by 2nd birthday
Legs will soon catch up and surpass the arms
• Neck lengthens by first birthday
Failure to Thrive (FTT)
• Organic FTT (OFTT)
– A biological underlying health problem accounts for infant’s
failure to obtain or make use of adequate nutrition.
– Does not make normal gains in weight
• Nonorganic FTT (NOFTT)
– A nonbiologically based underlying health problem accounts for
the infant’s failure to obtain or make use of adequate nutrition.
– Has psychological roots, social roots, or both
– Does not make normal gains in weight
Failure to Thrive Problems
• FTT infants typically have feeding problems.
– Variable eaters
– Less hungry
• Slow physical growth
• Cognitive, behavioral, and emotional problems
Catch-Up Growth
• Organic factors
– Illness and diet can slow child’s genetically determined growth
pattern
• If problem is addressed,
– child’s rate of growth frequently accelerates to approximate its
normal curve
– Referred to as canalization
Nutrition: Fueling Development
• Infant nutrition guidelines
– From birth, should be fed breast milk or iron-fortified infant
formula (first year or longer) AAP
– Solids generally introduced 4-6 months of age
– Cow’s milk should be delayed until 9-12 months of age
– Avoid overfeeding or underfeeding
– Provide some fat and cholesterol
– Do not overdo high-fiber foods
– Avoid added sugar and salt
– Encourage eating of high-iron foods
Breast Feeding versus Bottle Feeding
Past to present
• Breast feeding has become more popular
• 70% of American mothers now breast feed for some
time
Pros of breast milk
•
•
•
•
Considered to be the best nourishment for infants
Does not upset the infant’s stomach
Is adequate nourishment for first 6 months after birth
Conforms to human digestion processes & changes to
help meet infant’s changing needs.
Breast Feeding versus Bottle Feeding (cont’d)
Benefits for infant
Benefits for mother
• Improved immune system
functioning
• Reduces the risk of early
breast and ovarian cancer
• Protects against childhood
lymphoma
• Stronger bones and reduced
likelihood of hip fractures that
result from osteoporosis
following menopause
• Decreased likelihood of
– developing allergic responses
and constipation
– developing obesity later in life
– developing serious cases of
diarrhea
• Better neural and behavioral
organization
• Helps shrink uterus after
delivery
Pros of Bottle Feeding
• Allows for others to feed the infant
• Breasts are not sore and tender
• Mother is not sole provider for nourishment
Development of the Brain and Nervous
System
Development of the Brain and Nervous System
• People are born with 100 billion neurons.
– Each neuron has a cell body, dendrites, and an axon
– Dendrites
• Short fibers that extend from cell body and receive incoming
information
– Axon
• Extends trunk-like from the cell body and accounts for much of the
difference in length in neurons
– Neurotransmitters
• Message-carrying chemicals released from axon terminals
Fig. 4-2, p. 76
Myelin
• Myelin sheath
– Fatty, whitish substance that encases and insulates axons
• Myelination
– Process by which axons are coated with myelin
– Not completed at birth
– Myelination of brain’s prefrontal matter continues into the 2nd
decade of life
• Multiple sclerosis
– Myelin is replaced by hard, fibrous tissue that disrupts the timing
of neural transmission, interfering with muscle control
– PKU and congenital infection with HIV affect the myelination
process
Structures of the Brain
• Medulla
– Vital in the control of basic functions such as heartbeat and
respiration
– Part of brain stem
– Nerves that connect spinal cord to higher levels of the brain
pass through here
• Cerebellum
– Helps child maintain balance, control motor behavior, and
coordinate eye movements with bodily sensations
• Cerebrum
– Two hemispheres that become more wrinkled as child develops,
coming to show ridges and valleys called fissures
– Contributes to human learning, thought, memory, and language
Growth Spurts of the Brain
• Formation of neurons completed at birth
• First growth spurt
– During 4th and 5th month of prenatal development
– Due to formation of neurons
• Second growth spurt
– Between 25th week of prenatal development and the end of the
2nd year of life after birth
– Due to proliferation of dendrites and axon terminals
Fig. 4-3, p. 78
Brain Development in Infancy
• Myelination contributes to what infants are able to do.
• Reflexive functions such as breathing due to myelination
• Myelination of motor pathways allows neonates to show
stereotyped reflexes.
• Myelination will allow the disorganized movements of
the neonate to come under increasing control.
– Myelination of motor area of the cerebral cortex begins at
the 4th month of prenatal development.
– Myelination of the nerves to muscles is largely developed by the
age of 2 years.
– Some myelination continues to some degree into adolescence.
Brain Development in Infancy (cont’d)
• Sensory development
– Vision, hearing, and skin senses are less well myelinated at
birth.
– Myelination progresses and allows for increasingly complex and
integrated sensorimotor activities.
– Hearing
• Myelination begins at 6th month
• Continues through age 4
– Vision
• Myelination begins only shortly before full term
• Completes process by 5th or 6th month
Nature and Nurture in Brain Development
• Sensory stimulation and physical activity during early
infancy sparks growth of the cortex.
• Infants have more connections among neurons than
adults.
– Connections activated by experience survive
– Others are pruned
• Lack of stimulation
– Can impair motor development and adaptability
Motor Development
Motor Development
• Motor development follows cephalocaudal and
proximodistal patterns and differentiation.
• Neonates can lift head up aiding in avoiding suffocation.
– First they lift head
– Then they lift chest
• Heads must be supported when held
– Can hold up head between 3 to 6 months old
Fig. 4-6, p. 81
Control of the Hands: Getting a Grip
• 3 months
– Infants make clumsy, swiped movements toward objects
– Ulnar grasp
• 4 to 6 months
– Infants are more successful at grasping objects
– Can transfer objects back and forth between hands.
– Good age for giving rattles, large plastic spoons, mobiles, and
other brightly colored hanging toys that are kept out of reach
• 9 to 12 months
– Pincer grasp gives infants ability to pick up tiny objects
– Oppositional thumb comes into play
• 15 to 24 months
– Children show progression in stacking ability
Locomotion
• 6 months
– Infants roll over, turn from back to stomach
– Infants can sit if supported
• 7 months
– Infants usually sit on their own
• 8 to 9 months
– Infants begin to crawl or creep
– Standing overlaps with crawling and creeping
– May walk with support of adult
• 11 months
– Infants can pull themselves up
Locomotion (cont’d)
• 12 to 15 months
– Walk on their own, earning the name of toddler
– Run in bowlegged manner
– Fall easily because they are top heavy
• Some toddlers fall without notice and get back up
• Others cry
• Toddlers differentiate between shallow slopes and steep
ones, choosing to slide or crawl down steep ones
• Age 2
– Child can climb one step at a time, run well, walk backward, kick
a large ball, and jump several inches
Locomotion (cont’d)
• Myelination and differentiation of the motor areas of the
cortex must occur to master skills
• Neonate’s stepping and swimming reflexes
– disappear when cortical development inhibits some functions of
the lower brain
– reappear later, yet differ in quality
• Effects of training
– Early introduction to extensive motor skills training levels off
(Arnold Gesell study, 1929)
• Iranian infants (unlike Hopi children) in orphanage were
exposed to extreme social and physical deprivation
– They did not overcome motoric retardation (Dennis study, 1960)
Sensory and Perceptual Development
Visual Acuity, Peripheral Vision, and
Preference
• Neonates
– Extremely nearsighted at about 20/600
– Have poor peripheral vision
• Expands to 45 degrees by the age of 7 weeks
– Prefer stripes and curved lines
– Prefer and identify mother’s face
• After 8 hours of contact over 4 days
– Prefer edges of face such as chin
• May be due to attention to movement and contrast
• Most dramatic gains in visual acuity made between birth
and 6 months of age
– Acuity reaches about 20/50
• By 3 to 5 years,
– visual acuity generally approximates adult levels about 20/20
Fig. 4-7, p. 83
Fig. 4-8, p. 84
Depth Perception
• Infants generally respond to depth cues by 6 to 8
months
• Visual cliff study, Gibson and Walk (1960)
– Identified age at which infants have depth perception
– Ability to crawl indicated in ability to perceive depth
• Campos et al. (1970) study
– Heart rate increased when infants placed on edge of cliff at 9
months of age
– Newly walking infants more afraid of falling off
– Different postures involve the brain in different ways and
influence infants’ avoidance (Adolph, 2000)
Fig. 4-9, p. 85
Development of Perceptual Constancies
• Perceptual constancy
– Tendency to perceive an object to be the same even though the
sensations produced by the object may differ under various
conditions
• Size constancy
– Tendency to perceive the same objects as being the same size
even though their retinal sizes vary as a function of their
distance
– Present in early infancy (Bower, 1974)
• Shape constancy
– Tendency to perceive that the shape of objects remains the
same regardless of the retinal image being received
– At 4 to 5 months old, infants grasp shape constancy under
certain conditions.
Development of Hearing
• 1 month
– Infants perceive differences between speech sounds that are
similar.
– Infants exposed to normal backdrop of moderate noise levels
become habituated to them and not likely to awaken unless
there is a sharp, sudden noise.
• 3 ½ months
– Can discriminate parent’s voices
• 18 months
– Hearing is similar to adults’
• Exposure to native language causes gradual loss of
capacity to discriminate sounds that are not in their
native language
Development of Coordination of the Senses
• Young infants recognize that objects experienced by
one sense are the same as those experienced through
another sense.
• Five-month-old infants look at novel stimulation longer
than familiar sources of stimulation.
– Infants looked at unfamiliar objects longer than objects they had
held in their hands.
– This shows a transfer of information from the sense of touch to
the sense of vision
The Active-Passive Controversy in
Perceptual Development
• Changes in perceptual processes of children develop
from passive, mechanical reactors to the world into
active, purposeful seekers and organizers of sensory
information.
• These changes include
1) intentional action replacing “capture”
• automatic responses to stimulation
2) systematic search replacing unsystematic search
3) attention becoming selective
4) irrelevant information becoming ignored
The Role of Nature and Nurture
Evidence for the role of nature
• Neonates born with sensory skills and perceptual skills
– can see nearby objects, hearing is fine, able to track moving
objects, prefer certain kinds of stimuli
• Sensory and motor changes linked to maturation of
nervous system
Evidence for the role of nurture
• Children have critical periods in their perceptual
development.
– Failure to receive adequate sensory stimulation can result in
permanent sensory deficits
• Health problems with vision in child’s eye where patch
is needed extensively can result in permanent visual
impairment