Brain Development and Physical Growth

Brain Development

The Neuron

  • Basic Structure: The fundamental unit of the brain, responsible for transmitting electrical impulses.

  • Components:

    • Dendrite: Receives electrical impulses from other neurons.

    • Nucleus: Contains the cell's genetic material; located within the soma.

    • Soma (Cell Body): The main part of the neuron, responsible for maintaining the cell and processing signals.

    • Axon: Transmits electrical impulses away from the soma to other neurons.

    • Myelin Sheath: A fatty insulation layer around the axon that speeds up electrical impulse transmission.

    • Axon Terminal: The end of the axon where neurotransmitters are released to communicate with other neurons.

  • Direction of Electrical Impulse Travel: From dendrites, through the soma, down the axon, and to the axon terminals.

Synaptogenesis

  • Definition: The process of forming new synapses, which are the junctions between neurons where electrical or chemical signals are transmitted.

  • Significance: Crucial for brain development and learning, allowing for complex neural networks to form.

Arborization, Synaptogenesis, and Synaptic Pruning

  • Arborization: Refers to the branching and growth of dendrites, which increases the surface area for receiving synaptic connections. It's a key part of synapse formation.

  • Developmental Timeline of Synapse Formation (Arborization & Synaptogenesis):

    • 36 weeks gestation: Initial synapse formation begins.

    • Newborn: Continued formation of synapses.

    • 3 months: Significant increase in synaptic density.

    • 6 months: Further expansion of synaptic connections.

    • 2 years: Peak of synaptogenesis, with a very high density of synapses.

    • 4 years & 6 years: Synaptic density remains high but begins to be influenced by synaptic pruning.

  • Synaptic Pruning: The process by which excess or little-used synapses are eliminated to increase the efficiency of neural transmissions.

    • This is a crucial process for refining brain architecture and ensuring optimal function.

  • Synaptic Density Across Brain Regions and Age:

    • Visual Cortex: Reaches peak synaptic density earlier (around 2 to 4 years of age) and then undergoes pruning.

    • Prefrontal Cortex: Shows a slower trajectory, reaching peak synaptic density later (closer to 4 years and beyond) and continuing pruning into adolescence, reflecting its role in higher-order cognitive functions that develop later.

    • Generally, synaptic density is more dense in early childhood and less dense in adolescence and adulthood after pruning has occurred, leading to a more efficient, specialized brain.

Plasticity

  • Definition: The brain's remarkable capacity to be shaped, molded, or changed by experience.

  • Types of Plasticity:

    • Experience-Expectant Processes:

      • Reliance on Species-Typical Experiences: These processes rely on certain universal experiences that all members of a species are expected to encounter (e.g., seeing, hearing, having social interaction).

      • Brain's Readiness: The brain is

Sensitive Periods

  • Window of time when the brain is sensitive to certain kinds of environment inputs

  • Blakemore and Cooper (1970)

  • Sensitive period in humans” The Bucharest study: children raised in Romanian orphanages

Experience Dependent Processes

  • unique to the individuals environment

  • occurs throughout the lifespan

Physical Growth 

Basic Principles characterizing the growth process

  1. individuals do not develop at the same rate - distance curves illustrate how children grow at different rates and can vary significantly in height and weight during critical periods of development. This variability is influenced by a combination of genetic factors, nutritional status, and environmental conditions that together shape each child's growth trajectory. - Velocity curves depict changes in growth rate over time, providing insights into how quickly a child is growing at different ages and highlighting periods of rapid growth, such as during infancy and puberty.

  2. Cephalocaudal and proximodistal patterns of growth - head size - locomotor development - prehensile development

  3. Canalization: in any young animal, growth has a tendency to return to its original path or channel if circumstances have conspired to push it off course (self stabilizing or target seeking) catch up growth - increased velocity - maturity delayThis phenomenon indicates that even if a child experiences a temporary setback in growth due to illness or malnutrition, they may exhibit catch-up growth, characterized by an increased growth velocity in subsequent stages to reach their expected height and weight. This illustrates the resilience of the developmental process, where biological mechanisms work to stabilize growth and ensure that individuals achieve their genetically predetermined growth potential.

  4. Asynchronous rates of growth

Secular Trend: Marked changes in physical development that have occurred over generations : Age of menarche

Secular Trend: Obesity

Secular Trend: Childhood Obesity

  • Increased prevalence of overweight children due to factors such as diet, sedentary lifestyle, and environmental influences. Additionally, the rise of screen time and fast food consumption has contributed significantly to this growing concern, leading to long-term health implications for affected individuals.

  • What can explain the secular trend in childhood obesity: Diet : Greater availability of high calorie foods and sugar drinks

  • limited access to healthy affordable foods

  • larger portion sizes

  • lack of breastfeeding support

Exersize

  • lack of daily, quality physical activity in schools

  • lack of safe places to play or be active

  • television and media 

Sleep