Chapter 3.2 Physical Development

Rapid growth in early infancy requires high calories relative to body weight.
Feeding options to support growth:
- Breastfeeding is a great way to ensure proper nourishment.
- Bottle feeding with formula is an alternative.
- A combination of both feeding methods is possible.
Everyday guidance often phrased as: "you need to feed your child"; decisions vary.
Reasons mothers may not breastfeed vary; breastfeeding does not work for everyone.
In developed countries, bottle feeding with formula is typically safe due to clean water for mixing formula.
In underdeveloped countries, bottle feeding requires caution because water quality may be unsafe, increasing risk of passing unsafe water to newborns.
Practical implication: feeding method choice interacts with water safety and local conditions.

Global prevalence: about 1 in 4 children under age 5 are malnourished (UNICEF, 2016).
Consequences of malnutrition:
- Children tend to be small for their age due to inadequate nutrition.
- Malnutrition can cause substantial and possibly irreversible brain damage.
- Malnourished children are often listless, quiet, and possibly inactive.
United States context (note from transcript): about 11% of their nervous system.
- This line appears ambiguous in the transcript and may be intended to convey a related statistic about neurodevelopment or malnutrition impact in the US; please interpret with caution and corroborate from authoritative sources.

Nerve cells are neurons; key parts:
- Cell body
- Dendrites
- Axon
- Terminal buttons (synaptic terminals)
Terminal buttons release neurotransmitters.
The corpus callosum is the thick band of fibers connecting the two cerebral hemispheres.

Cerebral cortex: the wrinkled surface of the brain that regulates many functions.
Hemispheres: right hemisphere and left hemisphere.
The corpus callosum connects the two hemispheres (as above).

Weeks after conception: neural plate forms.
By $28\,\text{weeks}$ after conception, the brain will have about all the neurons that it ever will have.
Neurons migrate and become positioned into the six layers of the mature brain.
In the $4^{\text{th}}\text{ month}$ of prenatal development, axons begin to form the fatty myelin sheath (myelination).
The number of synapses in the brain peaks at $12\,\text{months}$ .
Synaptic pruning occurs: the brain reduces unnecessary synapses as they are no longer needed.

Experience-expectant growth: wiring of the brain organized by experiences common to most humans.
Experience-dependent growth: changes in the brain linked to unique experiences, not universal to everyone.
Both processes work together:
- Some wiring is universal across humans.
- Other wiring reflects individual family, culture, and life experiences.

Prompt: Comment on something that surprised you about infant brain development or nutrition.
Prompt: Ask a question about any topic covered to facilitate peer or instructor support.
Practical implications:
- Importance of safe feeding practices and clean water in feeding strategies.
- Global health disparities in malnutrition and access to safe feeding options.
- Early brain development is shaped by both universal experiences and culturally specific experiences.

Malnutrition prevalence: $rac{1}{4}$ of children under age 5 (UNICEF, 2016).
Critical prenatal milestone: $28\,\text{weeks}$ after conception marks near completion of neuronal population.
Peak synapses: $12\,\text{months}$ .
Myelination begins around the $4^{\text{th}}\text{ month}$ of prenatal development.
Hemispheric connections: corpus callosum as the connective tract between left and right hemispheres.

Nutrition in the first two years influences growth and brain development; both insufficient caloric intake and poor nutrient quality can have lasting effects.
Feeding choices are influenced by safety, cultural norms, and access to resources.
Early brain development involves both universal wiring and individual variation shaped by environment and experiences.