Chapter 2

Physical Development

The prenatal development period is the time

from conception to birth.

The human zygote is the cell that is formed by the union

of the sperm and ovum.

The human zygote contains one set of 23 chromosomes from the

mother and another set of 23 chromosomes from the father.

Polygenetic Traits

Human characteristics that result from the interplay of multiple genes.

skin color

height

A trait not expressed reflects

a recessive gene.

A DNA Molecule (Figure 2.2)

Males have an X and a Y chromosome.

Females have two X chromosomes.

Approximately 160 males are conceived for every 100 females.

Sex-linked Characteristics

Traits from recessive genes

that are carried on the sex chromosome.

Monozygotic twins come from the same fertilized egg and contain the same genetic

instructions.

Dizygotic twins develop from two different eggs.

Down Syndrome

• There is an extra twenty-first chromosome or a piece of one.

• The disorder occurs 1 out of 1,000 live births.

• Incidence has been linked to the age of the mother.

• Children have a very characteristic appearance.

Fragile-X Syndrome

• One of the leading causes of mental retardation and developmental disabilities

• Caused by a single gene• More common in males than females• Can be detected through genetic screening

and DNA analysis

Genotype

The genes a person inherits

from both parents for any particular trait.

Phenotype

The actual expression of inherited traits.

The average period of human gestation is 38 weeks.

Prenatal Development is divided into three major stages:

• germinal period

• embryonic period

• fetal period

Stages of Prenatal Development

Teratogen

Any environmental substance or disease that causes abnormal development of the fetus.

The most common and direct cause

of low birth weight is poor nutrition.

The human brain is the largest among land mammals relative to

body size.

The human brain is not fully mature until early adulthood.

The Central Nervous System

• consists of the brain, spinal cord, and nerve cells

• controls almost every aspect of human functioning

Left Side of the Brain (Figure 2.6)

Half of the neurons produced during prenatal development die.

Myelination

• process whereby the neurons and dendrites become coated with a fatty substance called myelin

• enables neural impulses to travel faster

The idea that there is a “critical period”

for brain development is an issue of debate.

Though often thought true, there is no strong

scientific evidence to categorize individual

differences in learning styles according to left- and right-brain

hemispheric specialization.

(Hiscock & Kinbourne, 1987)

Both cerebral hemispheres influence more aspects of

cognitive functioning than was previously thought.

Perceptual development involves the processing of

sensory information by the brain.

Habituation is the decrease in an infant’s response to a stimulus after repeated exposure to it.

Fetuses can react to sound.

Babies prefer sweet fluids to other tastes, and they dislike sour

and bitter tastes.

The sense of smell is present at birth.

Newborns are responsive to touch.

Attachment is the process by which infants form strong, affectional ties with their

caregivers.

Intermodal perception means that events or objects

can be simultaneously perceived by multiple senses.

Why does knowledge of children’s perceptual development

have important implications for educators?

Learning Disabilities

• are not due to a lack of motivation or effort on the child’s part

• is not due to poor teaching

• is not due to a lack of intelligence

• is not due to any temporary causes

Possible Causes for Learning Disabilities

• Heredity• Problems during pregnancy and birth• Incidents after birth

Children with specific learning disabilities exhibit a wide range of academic learning problems.

Potential Signs of Learning Disabilities, continued.

Attention Deficit Hyperactivity Disorder (ADHD)

• a commonly diagnosed behavior disorder

• characterized by developmentally inappropriate levels of activity, concentration, distractibility and impulsivity.

• more frequent in boys than in girls

Many physical disabilities result from damage to the central

nervous system.

Children with low vision cannot read newsprint-size letters, even

with corrective lenses.

Children who are blind have either 20/200 vision or a limited field of vision.

Traumatic Brain Injury

• an acquired injury to the brain

• either open or closed head injury

• has significant impact on learning

Children with deaf-blindness have dual sensory impairments.

The degree of integration into the general classroom depends on a child’s level of cognitive development and communication ability.

Autism

• a neurological disorder

• affects the functioning of the brain

• more common in boys than girls

By age 5 or 6, most children:

• can copy simple geometric shapes

• can manipulate buttons and zippers

• may be able to tie their own shoes

• can print the alphabet, letters in

their name, and numbers 1 - 10

• may write large and not well organized on paper

Girls tend to walk

earlier than boys.

By the early childhood years, boys outperform girls on most

gross motor tasks.

Children or adolescents with poor motor skills may avoid

physical activities and become sedentary.

Childhood obesity has been on the rise.

As motor skills develop and children begin to spend more time away from the careful supervision of parents, the

incidence of accidental injuries rises.

Too may children are pushed into competitive sports before their motor skills have significantly

matured.

The average infant weighs approximately

7.5 pounds at birth.

During the first year, an infant’s weight will triple.

Cephalocaudal Development

• Growth starts at the head and proceeds downward

• The infant’s brain, neck, and trunk develop before the legs

Proximal-distal Development

• Development begins in the center and proceeds outward.

• Organs develop before the arms or hands

Physical growth slows down during the preschool and

elementary years.

The average American is growing taller today.

Heredity plays an important role in determining

a child’s shape and size.

Nutrition is a core element of well-being throughout life.

Sleep is a vital component of health and well-being.

Puberty refers to the period in which a young person becomes capable of sexual reproduction.

Ethnic differences in the onset of puberty are not well understood.

Puberty is a dramatic period

of physical development, second only to infancy.

Puberty often leads to changes

in adolescents’ self-image, self-confidence, family relations,

moods, relations with the opposite sex,

and many other behaviors.

There is considerable individual variability

in the onset of puberty.

Early physical maturity in girls can have some

positive consequences, but it also poses some risks.

Young people today face a number of risks and challenges, including drug use, early sexual

experimentation, and AIDS.

FIGURE 2.13 Concerns of Children and Adolescents Today Source: Child Welfare League of America, 2005.

• In 2001, almost half of the total number of enrollees in Medicaid werechildren under age 19.

• In 2002, 425,493 babies were born to girls ages 15 to19, a birthrate of 43 per

1,000 girls.• In 2002, an estimated 2,209,000 children ages 12–17 were dependent on or

abusing illicit drugs or alcohol.• Co-occurring mental health and substance abuse disorders are increasingly

prevalent in youth; of youth treated for substance abuse disorders, 80–85% also have a mental health disorder.

• In 2003, 1,687,814 children under age 18 were arrested; of these arrests,25,531 were for violent crimes and 11,501 were for possession of a

weapon.• A 2001 census showed that 104,413 children are housed in juvenile correction facilities in the United States.• In 2001, 1,890 children under age 20 committed suicide in the United States,

a rate of 2.6 per 100,000 children.

The percentage of young people who are overweight has more

than doubled in the last 30 years.

Childhood obesity has increased rapidly in the last 30 years.

The eating disorder anorexia nervosa

mainly affectsadolescent girls

between the ages of 14 and 18.

Bulimia nervosa is an eating disorder in which one goes on an eating binge and then vomits or

uses laxatives as a way of purging the body.

It is commonly believed that drug problems

among young people are at an epidemic level

in the United Stated.

As a consequence of popular culture

and society’s relaxed attitudes about sexuality,

many researchers believe that young people

are dealing with sexual issues at a younger age than ever before.

Compared with adults, adolescents are at a higher risk

for acquiring sexually transmitted diseases (STDs), including HIV.

The problem that has received the most attention

is adolescent pregnancy.

Schools, like other ecological contexts, support healthy development of children and adolescents and prevent risky behavior.