🔑 Key Definitions
Critical Period: Specific developmental window when experience has maximal impact on neural organization; limited reversibility afterward
Teratogenic Effects: Harmful effects on developing fetus caused by drugs, chemicals, or environmental factors
Postnatal Development: Brain growth and refinement that continues after birth through childhood and adolescence
Malnutrition Effects: Irreversible brain damage caused by inadequate nutrition during critical developmental periods
Teratogenic Effects: Harmful effects on developing fetus caused by drugs, chemicals, or environmental factors
Postnatal Development: Brain growth and refinement that continues after birth through childhood and adolescence
Malnutrition Effects: Irreversible brain damage caused by inadequate nutrition during critical developmental periods
📊 Brain Weight Development Timeline
- Birth: Brain weighs approximately 350 grams (about 25% of adult weight)
- 6 months: Brain doubles to approximately 700 grams
- 2 years: Brain reaches approximately 1,000 grams (75% of adult weight)
- Adulthood: Brain reaches full weight of approximately 1,350 grams
🧠 Critical Influences on Postnatal Development
- Nutrition: Essential for myelination, synaptogenesis; deficiency causes irreversible cognitive impairment
- Oxygen Supply: Critical for energy-intensive brain development; hypoxia causes permanent damage
- Motor Activity: Physical movement stimulates cerebellar development and cortical refinement
- Drugs (Teratogens): Alcohol, prescription drugs, toxins can cause structural abnormalities and functional deficits
- External Stimulation: Sensory experiences drive synaptic pruning and circuit refinement
⚠️ Critical Period Characteristics
- Time-Limited: Specific windows for maximal plasticity in different systems
- System-Specific: Different brain regions have different critical periods
- Experience-Dependent: Normal development requires appropriate environmental input
- Limited Reversibility: Damage or deprivation during critical periods often permanent
💡 Exam Tips
- Remember brain weight progression: 350g → 700g (6mo) → 1000g (2yr) → 1350g (adult)
- Malnutrition during critical periods = irreversible damage (cannot be fixed later)
- Know the five major influences: nutrition, oxygen, motor activity, drugs, stimulation
- Critical periods are TIME-LIMITED - emphasize the importance of timing
- Teratogenic effects are dose-dependent and timing-dependent
- Brain grows fastest in first 2 years - most vulnerable period