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 & feet
fastest (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 during
adolescence
- 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 synapse
by 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 groups
before 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