Chapter 6 – Physical Development

I. Growth Patterns

Top down - cephalocaudal

- head develops first

- vital functions first (survival)

Center outward – proximodistal

- internal organs first

- trunk faster than arms & legs

- BUT in adolescence, hands & feetfastest (awkward)

II. Phases of growth

Infancy/early childhood (0-5)

• Rapid growth

• Nervous system

• Body size

Middle/late childhood (6-12)• Slower growth• 2" & 6 lbs/year

Adolescence (13-20)• Rapid growth• Body size (3-6" & 10-15 lbs)• Reproductive system

Puberty:

• girls: breast enlargement, growth spurt

• boys: testicle enlargement

Individual variability

Population trends

1.Bigger & heavier

100 years ago man = 5'7" woman= 5'3"

Today: man = 5'9" woman = 5'4"

2.Growth is earlier• Average age for menarche

- 100 years ago = 15- today = 13

3.Industrialized vs. 3rd-world• Better medical care• Nutrition

III. Environmental Effects on Growth

A. Nutrition

Provides energy

- Basic body functions

- Physical activity

- Growth, especially after birth

Special needs of infants

- higher proportion of calories

- more vitamins & minerals

Malnutrition (50% of kids)

- failure to grow normally

- delayed & smaller growth spurt

- critical period of 1-3

Nutritional diseases

Marasmus

- inadequate calories

- in 1st year

- from malnourished mother

- infant can die

Kwashiorkor

- inadequate protein

- ok while breast-fed

-> years 1-3

childhood illnesses

- weakened immune system

-> smaller, lower IQ, etc.

Over-nutrition

- heredity + environment

- physical illness

- social problems

B. Climate

Body types adapted to climates

east Africans vs. northern Asians

Seasonal variations in growth

- grow faster in spring & summer

C. Psychosocial Effects

1.Emotional stress

- “Failure to thrive”

- emotional traumas reduce growth hormone

- some catch up

2. Popularity & timing of puberty

Boys

- early maturation = better duringadolescence

- late-maturing boys benefit later;

more sensitive & flexible

Girls

- mixed results in girls

- disadvantages to early maturation

- but differences disappear

II. Central Nervous System (CNS)

• CNS = Brain & spinal cord

Neuron Structure

• Cell body - nucleus

• Dendrites - receive information

• Axon - sends information

• Myelin sheath - conductance

Neuron Function

• Impulse is carried across synapseby neurotransmitters

Brain structures & functions

Cerebrum/cortex

• Higher functions

• 2 hemispheres

(separated by corpus callosum)

• Left = language

• Right = visual-spatial, humor, perceiving emotions

4 Lobes

• Frontal - personality, executive, motor

• Parietal - speech, sensory

• Occipital - vision

• Temporal - hearing

Subcortex

Limbic system

- emotions, pleasure & aversion,

- sensory & motor impulses

Reticular formation

- sleep & wake

Cerebellum • Involuntary motor• Body equilibrium & muscle tone

Medulla• Reflexes

Spinal cord• Impulse conduction to body parts

Brain Development

Brain size

• 25% of ultimate size by birth

• 90% by age 5

Number of neurons

• Born with total number

• Grow in size & connections

Lateralization development

• left: language from roughly birth

• right: inconsistent research

III. Motor Development

Principles

1.Gross before fine

Coordination of large muscle groupsbefore small muscle groups

2.Differentiation

• Learn to control specific muscles to enact specific behaviors

3.Integration

• Put individual, differentiated actions together into complex movements

Gross Motor Control(large muscles)

Control over upper body

• Holds chest/head up (3 mos)

Control over whole body

• Sits unsupported (5 mos)

Gets into sitting position (7 mos

• Spontaneous kicking

• Alternating leg movements

Pulls to standing (7-8 mos)

Crawls - 10 months

• Stands alone (11 mos)

• Walks (> 1 year)

• Refines walking (1-2 yrs)

• Uses 2 feet together (2 yrs)

• Full body control (6 yrs)

- boys better by 12

• Cultural differences in milestones

Fine Motor Control(small muscles)

Newborns: grasping reflex

- & sometimes hand to mouth

1-2 months - decline in grasping reflex

- visually-guided reaching

(good by 3 months)

- but touch objects only on same side of body as arm

4 months

- reach inward to body midline

- use 2 hands simultaneously

5 months

- coordinated actions with both hands

7-8 months

- sequence of behaviors with hands

18 months

- improved finger control

8-10 years

- skills close to adults

Handedness

• 90% = right hand; 7-8% = left hand

• Across cultures & 50 centuries

• Preference by age 1

• Consistent by age 3

Reasons for Right-Handedness

Environmental

• R-handed world

• Lefties forced to use right hand

• But R-hand consistency across cultures

Age-Handedness Correlation:

• With increase in age = fewer lefties

• Because older folks forced to use R hand?

• BUT - lefties die at earlier ages

• Women = 5 years Men= 10 years

• Safety

Genetic: recessive trait?

• But only 35% kids of 2 lefty parents are L-handed

• MZ twins not more alike than DZ twins

• DZ twins not more alike than unrelated people

Other biological• Related L-hemisphere dominance • Unknown mechanisms• Birth-related trauma?

disrupt normal hemispheric organization?

- greater neurological problems & birth stress

• More lefties develop Alzheimers

Determinants of Motor Development

Physical maturation - Nature

• Cross-cultural similarity

• Perform many behaviors without learning/practice

EX Navajos & walking

Learning - Nurture

• Activity changes brain

• Many behaviors must be practiced - Ache

• Some cultural differences

• Training can speed motor development

Conclusion: biology + environment