4. Physical and Motor Development

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4. Physical and Motor Development

• 4.1 Physical Growth
• 4.2 Problems of Physical Growth
• 4.3 The Developing Nervous System
• 4.4 Motor Development

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4.1 Physical Growth

• Features of Human Growth
• Variations on the Average Profile
• Mechanisms of Physical Growth
• The Adolescent Growth Spurt and Puberty

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Features of Growth

• Between birth and 2 years, average height
  increases from 19 to 32 inches and average weight
  increases from 7 to 22 pounds.
• As a rule of thumb, girls achieve half of their
  adult by 18 months and boys by 2 years.
• Increases in height and weight are not steady but
  come in spurts.

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Features of Growth

• Growth is rapid in the first year, fairly steady
  in preschool and elementary school, but is rapid
  again in early adolescence where a teen can grow
  4 inches and gain 16 pounds each year.

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Figure 4-2
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Features of Growth

• Cephalocaudal the head and trunk develop first.
  Toddlers have disproportionately large heads and
  trunks making them look top heavy.

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Features of Growth

• Important internal changes of physical growth are
  muscle, fat and bones. All of the bodies muscle
  fibers are present at birth which become longer
  and thicker, as fibers fuse together.

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Features of Growth

• A layer of fat forms under the skin during the
  last month of fetal development and accumulates
  rapidly during the first year after birth.
  Children become leaner during elementary school
  but begin to acquire fat during adolescence.
  Girls more than boys.
• Bone forms during prenatal development.

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Features of Growth

• Bone starts as cartilage and shortly after birth
  cartilage structures known as epiphyses turn to
  bone. Working from the center, cartilage
  gradually turns to bone working from the center
  toward the end. When the enlarging center turns
  to bone and reaches the epiphyses, growth is
  complete.

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Variations on the Average Profile

• Over historical time adults and children are
  taller and heavier than previous generations.
  These changes in physical development are known
  as the Secular Trend.

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Variations on the Average

• Across cultures average growth can also vary.
  Average and normal are not the same. A child can
  be shorter or taller than average and still be
  normal.

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Figure 4-3
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Mechanisms of Physical Growth

• Heredity--timing and end product is in the genes.
• Both parents contribute to the childs height.
  Short parents have short children, tall parents
  have tall children, etc.

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Hormones

• Hormones are chemicals that are released by the
  glands and travel in the bloodstream to act on
  other body parts. The pituitary gland, in the
  brain, and secretes growth hormone (GH) while you
  sleep and during exercise.

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Hormones

• GH travels to the liver and triggers the release
  of another hormone, somatomedin, which causes
  muscles and bones to grow.
• Without adequate amounts of GH, a child can
  become a dwarf.

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Hormones

• Another hormone, thyroxine, released by the
  thyroid gland is essential for the proper
  development of nerve cells. Without thyroxine,
  mental retardation and retardation of physical
  growth can occur.

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Nutrition

• Nutrition--growth is hard work, so the body needs
  calories to grow. Nutrition is particularly
  important during infancy when physical growth is
  rapid. Because growth requires energy, babies
  consume enormous numbers of calories.

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Nutrition

• Breast feeding is the best food for ensuring
  nourishment. Breast fed babies are less often
  ill due to immunities in the mothers system that
  are passed on to the child. These babies are
  also less prone to diarrhea or constipation and
  they typically make the transition to solid more
  easily.

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Nutrition

• Formula prepared under sanitary conditions is
  nourishing but infants may develop allergies and
  are not protected from diseases. Growth slows
  down for 2 year olds and they become more finicky
  about foods. Adolescents need to eat more to
  prepare for the adolescent growth spurt.

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The Adolescent Growth Spurt and Puberty

• Onset Events and timing differ for boys and
  girls, girls reach mature stature around 15 and
  boys around 17 yrs.
• This adolescent growth spurt is collectively
  known as puberty and also includes maturation of
  the reproductive system.

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Adolescent Growth Spurt

• For girls, puberty begins with growth of breasts,
  the growth spurt, and the appearance of pubic
  hair. The onset of Menarche typically occurs at
  age 13 yrs.
• For boys, puberty starts with the growth of the
  testes and scrotum, followed by pubic hair, the
  growth spurt and the growth of the penis. At
  about 13 yrs., boys usually have the first
  spontaneous ejaculation.

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Adolescent Growth Spurt

• Early maturation for boys might be around age 11
  and late maturation as late as 15 or 16. Early
  maturation for girls starts around age 9 and late
  maturation as late as 14 or 15. Genetics partly
  control the process with family experiences
  having an affect on girls menarche onset.

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Adolescent Growth Spurt

• Early or late maturation has psychological
  consequences that differ for boys and girls.
• Typically early maturation benefits boys and is
  detrimental to girls. Why? Sometimes rate of
  maturation can lead to events that choose a path
  for development to follow for life.

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Adolescent Growth

• Sexuality becomes a central issue for teenagers.
  Sex is emphasized on television, in movies, and
  seems to establish adult status.
• By the end of adolescence, most American boys and
  girls have had intercourse at least once.

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Adolescent Growth

• Adolescent sexuality likely to be more positive
  when peers and parents have positive attitudes.
• Adolescent sexual behavior causes approx. 1 in 10
  American teens to become pregnant. 60 give
  birth and 40 abort resulting in 500,000 babies
  born to teens annually.

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Adolescent Growth

• African American and Hispanic American females
  are the most likely to become teen moms while
  Asian American teens are the least likely.
• Teen mothers and their children usually face
  bleak futures. Why are there so many teen
  pregnancies?

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Adolescent Growth

• Very few sexually active teenagers use birth
  control. Those who do often use ineffective
  methods. Lack of contraceptive use can be
  attributed to Ignorance, many teens are
  misinformed. Illusion of invincibility, teens
  deny reality and think it cant happen to them.

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Adolescent Growth

• Lack of motivation, for some girls, becoming
  pregnant is a way out, out of their parents
  house, independent living, and having someone to
  love them. Lack of access, some teens dont know
  where to obtain contraceptives or are embarrassed
  to buy them. The best way to deal with this
  situation is to give teens the facts through
  effective education programs.

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Adolescent Growth

• Sexual orientation Roughly 15 of teens are
  attracted to members of their own sex. After role
  experimentation, about 5 of teens identify their
  sexual orientation as gay or lesbian.

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Adolescent Growth

• Scientists believe that sexual orientation is
  probably rooted in biology. Evidence suggests
  that heredity and hormones may influence sexual
  orientation. Many falsehoods exist regarding
  sexual orientation and should be dispelled.

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4.2 Problems of Physical Growth

• Malnutrition
• Anorexia and Bulimia
• Obesity

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Malnutrition

• Worldwide 1 in 3 children under 5 yrs of age is
  malnourished. Malnutrition is defined as being
  small for ones age.
• Not just a problem in 3rd World countries because
  20 of American children lack enough iron and 10
  go to bed hungry.

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Malnutrition

• Malnourishment is very damaging during infancy
  because growth is so rapid. A longitudinal study
  in Barbados followed a 2 groups of children, one
  was severely malnourished during infancy, the
  other had similar families but had adequate food.

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Malnutrition

• When the children were older, they were
  indistinguishable physically but the children who
  were malnourished had much lower IQ scores. They
  also had difficulty paying attention and were
  easily distracted. Malnourishment results in
  brain damage affecting intelligence and attention
  span.

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Malnutrition

• Malnourished children are also lethargic to
  conserve energy but this inactively will cause
  profound changes in experiences that shape a
  childs development. More food is only part of
  the solution parents must be taught to foster
  their childrens development.

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Malnutrition

• Malnutrition must be fought on both the
  biological and sociological level. Programs that
  offer dietary supplements and parent training
  offer promise for the future.

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Anorexia and Bulimia

• Anorexia is the persistent refusal to eat and an
  irrational fear of being overweight. Individuals
  with this disease have a very distorted body
  image. Anorexia is a serious disorder that can
  lead to heart damage and death.

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Anorexia and Bulimia

• Bulimiais the alternation between uncontrolled
  eating and purging through vomiting or laxatives.
• Both primarily affect adolescent girls who are
  well behaved, conscientious, and good students.

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Anorexia and Bulimia

• Nature and nurture both play a role. Influenced
  by cultural standards for thinness and a change
  in their bodies due to puberty, adolescent girls
  begin dieting to lose weight.

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Anorexia and Bulimia

• Family dynamics can contribute to anorexia.
  Parents who are autocratic leave their
  adolescents with little sense of self-control.
  The girls assert autonomy to achieve identity.
  Heredity may contribute to these disorders in the
  form of a personality that tends to be rigid and
  anxious.

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Obesity

• Typically 5 10 of American are obese which
  refers to individuals who are at least 20 over
  their ideal body weight for their age and height.
• Obesity reflects heredity by influencing activity
  level and basal metabolic rate.

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Obesity

• The environment is influential as well.
  Television ads encourage eating, usually
  fattening foods.
• Parents also play a role by inadvertently
  encouraging external instead of internal cues for
  satiation, e.g., clean your plate.

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Obesity

• Weight loss for youth is possible. Programs that
  are successful have these features encourage
  activity, not sedentary behavior learning to
  monitor eating and exercise train parents to
  help set realistic goals and use behavioral
  principles.

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4.3 The Developing Nervous System

• Organization of the Mature Brain
• Making of the Working Brain

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Brain Organization

• The basic unit of the brain is the neuron, a cell
  that specializes in receiving and transmitting
  information. The mature brain is organized by
  function.
• The receiving end of the neuron is the dendrite.

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Brain Organization

• The dendrite looks like a tree with branches and
  allows the neuron to receive input from thousands
  of other neurons.
• The tube like structure at the other end of the
  cell is the axon, which sends information to
  other neurons.

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Brain Organization

• The axon is wrapped in a fatty sheath called
  myelin, which speeds the transmission of
  information.
• At the end of the axons are terminal buttons that
  release chemicals, called neurotransmitters, that
  carry information to nearby neurons. Axons and
  dendrites dont touch but are separated by a gap
  called a synapse. Neurotransmitters cross the
  synapses.

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Figure 4-6
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The Developing Brain

• Emerging brain structures
• Structure and function
• Brain plasticity

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Emerging Brain Structures

• Three weeks after conception, a group of cells
  form a flat structure called the neural plate.
  At 4 weeks, the plate folds to form a tube that
  becomes the brain and spinal cord.
• Production of neurons begins 10 weeks after
  conception and by 28 weeks has all the neurons it
  will ever have.

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Emerging Brain Structures

• Neurons form at an incredible rate of 4000 per
  second and migrate to final positions in the
  brain. The brain is built in stages beginning
  with the inner most layer and continuing until
  all 6 layers are in place approximately 7 months
  after conception.

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Emerging Brain Structures

• The axons acquire myelin beginning around the 4th
  month after conception.
• Myelination continues through infancy and into
  childhood and adolescence.
• Neurons that carry sensory information are
  myelinated first and the cortex last.

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Emerging Brain Structures

• In the months after birth, the brain grows
  rapidly. As the number of dendrites increases so
  do the synapses, reaching a peak at the 1st
  birthday.
• After rapid brain growth, unused synapses begin
  to disappear gradually called synaptic pruning.

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Emerging Brain Structures

• Continuing into adolescence the brain goes
  through its own version of downsizing, weeding
  out unnecessary connections.

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Structure and Function

• Brain structure and function is revealed from
  studies of children with brain injuries. If a
  region regulates function then damage to that
  area will impair function.

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Structure and Function

• Studies of electrical activity or EEGs help to
  pinpoint areas of function by showing distinctive
  EEG patterns.
• Studies using imaging techniques will show
  function through blood flow and use of glucose.
  F-MRI (magnetic fields to trace blood flow) PET
  Scan traces glucose usage in the brain.

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Structure and Function

• Many brain regions specialize early in life. For
  example, EEG studies show in infant brains the
  left hemisphere generates more activity in
  response to speech than the right.

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Structure and Function

• At birth, the left hemisphere is already
  specialized for language processing and verbal
  function.
• The right hemisphere is more active to music and
  has been implicated in spatial relations and
  recognizing faces.

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Structure and Function

• The activity in the frontal cortex increases
  after birth and resembles adult levels by 7-8
  months after birth.
• The frontal cortex regulates goal-directed
  behavior.

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Structure and Function

• Overriding responses that are incorrect or
  inappropriate is an important part of goal
  directed behavior. Children gradually become
  able to regulate their behavior to reach
  cognitive and social goals.

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Structure and Function

• The frontal also regulates feelings such as
  happiness, sadness, and fear.
• Nathan Fox and others have shown that the left
  frontal cortex regulates emotions having an
  approach tendency, e.g., happiness and curiosity
  and the right frontal cortex regulates avoidance
  emotions like distress, fear, and disgust.

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Research Focus

• Who were the investigators?
• What was the aim of the study?
• How did the investigators measure the topic of
  interest?
• Who were the children? What was the design? Were
  there ethical concerns?
• What were the results and conclusion?

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Research Focus

• Highlights show that the brain specializes early
  in life. Language processing is associated with
  the left hemisphere recognizing nonspeech
  sounds, emotions, and faces is associated with
  the right hemisphere while regulating emotions
  and intentional behavior is a function of the
  frontal cortex.

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Brain Localization

• The typical pattern of brain localization has
  been described previously but in some left-handed
  individuals the pattern is reversed from the
  usual.
• In cases of brain injury, cognitive functions are
  usually impaired, but over time, some function is
  restored.

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Brain Plasticity

• Flexible brain organization is shown by
  children who recover from brain damage.
• Brain organization is neither completely plastic
  nor completely rigid.

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Brain Plasticity

• The brains organization and function can be can
  be affected by experience but its development
  follows general biochemical instructions that
  ensure that most people end up with brain
  organization along the similar lines.

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4.4 Motor Development

• Locomotion
• Fine-motor Skills
• Maturation, Experience, and Motor Skill

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Locomotion

• Differentiation of component skills (posture and
  balance, stepping, perceptual skill)
• Integration of different component skills

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Fine-Motor Skills

• Reaching and grasping becomes more coordinated
  throughout infancy.
• Toddlers prefer to use one hand and this
  preference becomes stronger during the preschool
  years.

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Maturation, Experience, and Motor Skill

• Maturation is important Studies of Hopi infants.
• Experience matters, too African infants and
  training studies