Lecture 2 - BS3580

Brain Development

• Interconnectedness: Developing brain and behavior changes are closely linked; the complexity in brain interconnections underlies behavioral complexity, with specific emphasis on critical periods for sensory and cognitive development.

• Social Perception: Adequately developed neural circuits are crucial for social cognition, enabling an understanding of social cues and interactions.

• Development Timeline Example:

  • 3 weeks: Initial formation of the spinal cord and midbrain, establishing foundational structures for nervous system development.

  • 7 weeks: Development of hindbrain, midbrain, and forebrain structures, setting the stage for differentiated brain functions.

  • 11 weeks: Major brain structures become visible, indicating progression toward functional maturity.

  • At birth: Established morphology is achieved through folding and growth processes, leading to the complex architecture of the human brain.

Central Nervous System Structure

• Key Components:

  • Cerebrum: Largest component of the brain, involved in higher-order functions including thought, action, and emotion.

  • Basal ganglia: Plays a key role in movement regulation and coordination.

  • Diencephalon: Integrates sensory information and regulates autonomic functions.

  • Midbrain: Associated with vision, hearing, motor control, and alertness.

  • Cerebellum: Essential for coordination, precision, and accurate timing of movements.

  • Brainstem: Maintains basic life functions such as respiration and heart rate.

  • Spinal cord: Acts as the main pathway for transmitting information between the brain and body.

• Cerebral Cortex Functions:

  • Gray matter: Responsible for processing information, cognition, emotional behavior, and memory through complex networks of neurons.

  • White matter: Facilitates signal transmission between different areas of gray matter, consisting of myelinated axons that improve the speed of communication.

Stages of Brain Development

• 2. Neurogenesis: The birth of neurons and glial cells; crucial for forming the foundational cellular architecture.

• 4. Cell Migration: Cells migrate to designated areas, guided by molecular signals, to establish their functional locations.

• 6. Cell Differentiation: Non-specific progenitor cells become specialized neuron types based on intrinsic and extrinsic factors.

• 8. Cell Maturation: Development of dendrites and axons, critical for establishing synaptic connections.

• Synaptogenesis: Formation of synapses, where neurons connect and communicate, influencing network properties.

• Cell Death and Synaptic Pruning: Regulated elimination of surplus neurons and synapses, optimizing connectivity for efficient processing.

• Myelogenesis: Formation of myelin sheaths around axons, enhancing signal conducting speed and improving neural communication.

Neurogenesis Details

• Completed by week 20, generating approximately 250,000 neurons per minute at peak rates; this intensity underscores the rapid establishment of brain circuitry.

• Neurogenesis continues for a year or two post-birth, particularly in key areas of the brain associated with learning and memory, such as the hippocampus.

Adult Neurogenesis

• Involves the formation of mature neurons from neural stem cells within restricted brain regions, critical for restructuring neural circuits.

• Key areas include:

  • Subgranular zone of the hippocampus: Integral for memory formation and navigation.

  • Subventricular zone (SVZ): Sends migrating cells to olfactory bulbs, essential for repair and regeneration within the nervous system.

Key Mechanisms in Cortical Development

• Cellular Changes: Neuroepithelium, originating from the ventricular zone (VZ), transforms, migrates, and differentiates to build the cerebral cortex's layered structure.

• Radial Glial Cells: Serve as scaffolding for migrating neuroblasts and help maintain their orientation by forming attachments to both apical and basal surfaces of the developing cortex.

Axon Migration and Pathfinding

• Neurons are polarized, exhibiting a single axon along with multiple dendrites for effective communication.

• Growth Cones: Specialized structures at the axon tip that extend outwards; filopodia within growth cones dynamically explore the environment for guidance cues.

• Directional Growth: Driven by actin polymerization, growth cones respond to extracellular signals that influence attraction or repulsion to guide axon trajectory toward target regions.

• Cellular Mechanisms: Local RNA and protein synthesis within growth cones governs growth direction, enabling fine-tuned responses to environmental cues.

• Synapse Formation: Initiated when axonal filopodia contact dendrites, inducing the assembly of presynaptic and postsynaptic structures critical for functional synapses.

Apoptosis and Synaptic Pruning

• Neurons typically undergo apoptosis unless supported by neurotrophic factors (e.g., nerve growth factor), which provide survival signals and promote healthy synaptic connections.

• Synaptic Pruning: Involves the selective elimination of less active synapses; this process is crucial for refining neural circuits and optimizing brain function during development.

Levels of Information Processing

• Outlines the processing levels from molecular interactions to system-wide dynamics, integrating numerous interactions and responses in the nervous system, revealing the complexity of neuronal communication and computation.

Computational Models in Neuroscience

• Essential tools employed to study intricate neuronal interactions and predict behavioral outcomes within the nervous system, facilitating comprehensive understanding of brain function.

• Such models enable exploration of hypothetical scenarios and influence experimental designs, aiding in the facilitation of breakthroughs in neuroscience research.

Synaptic Mechanisms in Invertebrates

• The Giant Fiber System in Drosophila: A model system utilized to investigate rapid neural responses via large identifiable neurons, providing insights into basic principles of neuronal function.

• Modeling: Incorporates electrical and chemical synapse dynamics, underlining their roles in rapid action potential propagation, which is foundational for understanding neural circuit responsiveness.