Physical Development:�Prenatal Development, Infancy & Childhood

Module 3.2a

Conception

• At conception, genes on the 23 chromosomes from your biological mother’s ovum were paired with the genes on the 23 chromosomes contributed by your biological father’s sperm, creating your unique genetic makeup.
• Multiple gene pairs are involved in directing many complex features of development.

Overview of Genetics

• Chromosomes are long twisted strands of deoxyribonucleic acid (DNA) and are found in the nucleus of the cell
• Humans have 23 pairs of chromosomes
• DNA is the chemical basis of heredity and carries instructions
• DNA code carried on each chromosome is arranged in thousands of segments called genes.
• Genes are the basic unit of heredity

Prenatal Development

• Prenatal defined as “before birth”
• Prenatal stage begins at conception and ends with the birth of the child.
• At conception, chromosomes from the biological mother and father combine to form a single cell - the fertilized egg, or zygote.
• The prenatal stage has three distinct phases:
1. Germinal period -first two weeks after conception
2. Embryonic period - weeks three through eight
3. Fetal period - two months after conception until birth

Zygote

• A newly fertilized egg
• The first two weeks are a period of rapid cell division.
• Attaches to the mother’s uterine wall
• At the end of 14 days becomes a cluster of cells called an embryo.

Embryo

• Developing human from about 14 days until the end of the eighth week
• Time of rapid growth and intensive cell differentiation
• Zygote’s inner cells become the Embryo
• Most of the major organs are formed during this time.
• Genes on the sex chromosomes and hormonal influences trigger the initial development of the sex organs
• At the end of the eighth week the fetal period begins.
• The embryo is protectively housed in the fluid-filled amniotic sac; the embryo’s lifeline is the umbilical cord.
• Via the umbilical cord, the embryo receives nutrients, oxygen, and water and gets rid of carbon monoxide and other wastes

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Placenta

• Zygote’s outer cells become the Placenta
• A cushion of cells in the mother by which the fetus receives oxygen and nutrition
• Acts as a filter to screen out substances that could harm the fetus
• The umbilical cord attaches the embryo to the placenta, a disk-shaped tissue on the mother’s uterine wall.
• The placenta prevents the mother’s blood from mingling with that of the developing embryo, acting as a filter to prevent some, but not all, harmful substances that might be present in the mother’s blood from reaching the embryo

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Fetal Period

• The period between the beginning of the ninth week until birth
• By the end of the third month, the fetus can move its arms, legs, mouth, and head
• During the fourth month, the mother experiences quickening—she can feel the fetus moving.

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• By the fifth month, the fetus has distinct sleep–wake cycles and periods of activity.
• During the sixth month, the fetus’s brain activity becomes similar to that of a newborn baby.
• During the final two months, the fetus will double in weight.

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See the changes that occur in prenatal development in this quick video

Prenatal Factors that Influence Development

• Nutrition
• Anxiety
• Mother’s general health
• Maternal age
• Teratogens -any agent that causes a birth defect (e.g., drugs, radiation, viruses)

Teratogens

• Substances that pass through the placenta’s screen and prevent the fetus from developing normally
• Teratogens include:
• Exposure to radiation
• Diseases, such as rubella, syphilis, genital herpes, and AIDS
• Toxic industrial chemicals, such as mercury, lead and PCBs
• Drugs taken by the mother, such as alcohol, nicotine, cocaine, and heroin

Fetal Alcohol Syndrome

• Cluster of defects occurring in infants born to mothers that drink heavily during pregnancy
• Leading cause of intellectual disabilities
• Epigenetic Effect – alcohol alters the chemical markers on DNA that switch certain genes on or off.
• Can be totally prevented by abstaining from alcohol during pregnancy

Physical & Psychological Development Are Related:

• Physical development begins at conception
• Physical maturity sets limits on psychological ability
• Visual system not fully functional at birth
• Ability to understand language not functional until much later
• Prenatal environment can have lifetime influence on health and intellectual ability

Infant Abilities

• Infants are born with immature visual system
• can detect movement and large objects
• Other senses function well on day 1
• will orient to sounds
• turn away from unpleasant odors
• prefer sweet to sour tastes
• Senses are keenly attuned to people, helping the infant quickly learn to differentiate between the mother and other humans.
• Born with a number of reflex behaviors

Newborn and APGAR Readings

• Watch “Testing Competency In a Newborn”
• Video #13 from Worth’s Digital Media Archive DVD (2 min)
• A = Activity or Muscle Tone
• P = Pulse (100 beats per minute)
• G = Grimace (sneeze & cough to suction of nose & mouth)
• A = Appearance (normal skin color)
• R = Respiration (cry & breath regularly)

Click Here to Play in Separate Window

Infant Reflexes

• Reflex is an automatic, unlearned response
• Rooting - turning the head and opening the mouth in the direction of a touch on the cheek. Child is looking for nourishment.
• Sucking - sucking rhythmically in response to oral stimulation
• Grasping - curling the fingers around an object
• Babinski - fanning and curling toes when foot is stroked
• Moro/Startle - throwing the arms out, arching the back and bringing the arms together as if to hold onto something (in response to loud noise or sudden change in position of the head)
• Swimming - if submerged, infants hold breath and pump arms & legs
• Stepping - move feet up and down when held up over a flat surface

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Reflexes in the Newborn

• Watch “Reflexes in the Newborn” (2 min)
• Video #14 from Worth’s Digital Media Archive DVD

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What do Newborns Know & Understand?

• Scientists capitalize on what babies can do – stare/gaze, suck, turn their heads
• Find out what newborns prefer by seeing what they turn their head towards or what they stare at.
• Babies tend to gravitate towards sights and sounds that bring social responsiveness
• Babies prefer sights, sounds, and smells associated with their caregiver.

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• Habituation – Decreased responding to a repeated stimulus
• Babies get bored with something they’ve experienced before and look away and stare longer at things that are new or surprising.

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Infant, Toddler, Child

• Infant: First year
• Toddler: From about 1 year to 3 years of age
• Child: Span between toddler and teen

Maturation

• Orderly sequence of biological growth
• Common course of development for most humans
• Maturation (Nature) sets the basic course of development: Experience (Nurture) adjusts it.

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Brain Development

• At birth, the newborn’s brain is 25% of its adult weight; its birth weight, by contrast, is 5% of its eventual adult weight
• By the end of infancy a baby’s brain will be 75% of its adult weight but their body and height will be about 20%
• Newborns enter the world with an estimated 23 billion neurons. After birth, the brain continues to develop rapidly.
• The number of dendrites increases dramatically during the first two years of life as experience helps form connections.
• From 3 to 6, front lobes show rapid growth (rational planning)
• Association Areas (thinking, memory & language) last areas to develop
• The axons of many neurons acquire myelin, the white, fatty covering that increases a neuron’s communication speed.
• Synaptic Pruning Process - As time goes on, neurons not used are eliminated or rewired (Use it or Lose it) – Happens mostly at puberty

Neural Development

Rapid growth of dendritic connections followed by synaptic pruning around puberty.

Environmental Influences on �Brain Development

• More Experience = Bigger Brain with More Connections!
• Rat’s brains in the enriched environment increased in weight by 7-10%
• Synaptic Connections increased by 20%
• Humans in impoverished environments show slowed brain & cognitive development
• Brain maturation (Nature) provides with neural connections while experiences (Nurture) activate and strengthen some while allowing unused connections to disappear (Use it or Lose it)

Sensitive/Critical Periods

• A sensitive period where the brain requires exposure to certain kinds of experiences in order to develop certain abilities/skills properly

Motor Development

• Includes all physical skills and muscular coordination
• Gross Motor Skills – moving large muscles and whole body
• Fine Motor Skills – precise, small muscle movements
• The basic sequence of motor skill development during infancy is universal although environment may help slightly speed up or slow down the process.
• Each infant has his or her own genetically programmed timetable of physical maturation and developmental readiness to master different motor skills.
• Watch “Baby Body Sense” (11:00)
• Segment #24 from Scientific American Frontiers DVD

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Infant Memory

• Infantile Amnesia – inability to remember events from before our 3^rd birthday
• Hippocampus & Frontal Lobes not fully mature until adolescence
• Brain does show ability to process & store memories before age 3
• Carolyn Rovee-Collier mobile experiment - babies learn to move a familiar mobile moving their leg and show a memory for this.