Lecture 6 Recording_Segment 2 Brain Growth and Development_20241017 KGan

Introduction to Brain Growth and Development

  • Overview of brain development from the neural tube:

    • Importance of understanding how different neural cells develop from the neural tube.

    • Focus on central nervous system (CNS) and peripheral nervous system (PNS).

Central and Peripheral Nervous Systems

  • Central Nervous System (CNS):

    • Composed of the brain and spinal cord.

  • Peripheral Nervous System (PNS):

    • Consists of nerves that connect the brain to the rest of the body.

Types of Neural Cells

  • Neurons:

    • Electrically excitable cells that transmit signals via electrical impulses.

  • Glial Cells (Glia):

    • Non-neural supporting cells that secrete growth factors and nutrients, influencing neuron development and connectivity.

Structure of Neurons

  • Parts of a Neuron:

    • Cell Body:

      • Contains the nucleus and organelles.

    • Dendrites:

      • Short, branched extensions that receive information from other neurons.

      • Dendritic spines serve as connection points for synapses.

    • Axon:

      • Long, thin extension that transmits signals away from the cell body to other neurons or muscles.

      • Length allows for connection with distant neurons.

Signal Transmission

  • Neurons communicate through action potentials:

    • Stimulation opens voltage-sensitive ion channels, primarily sodium channels, which generate electrical signals.

    • Action potentials propagate along the axon.

  • Synapse Structure:

    • Composed of presynaptic terminal (axon end) and postsynaptic terminal (dendrite end).

    • Vesicles in the presynaptic terminal contain neurotransmitters (e.g., GABA, glutamate).

Different Neural Cells

  • Mechanism of neurotransmitter release:

    • Membrane depolarization causes calcium influx, leading to vesicle docking and fusion, resulting in neurotransmitter release into the synaptic cleft.

    • Neurotransmitters bind to postsynaptic receptors on the receiving neuron, facilitating signal transmission.

  • Microglia:

    • The immune cells of the nervous system, originating from the neural tube.

Neural Tube Structure

  • Cross-sectional Zones of the Neural Tube:

    • Ventricular Zone:

      • Site of new neural cell birth and source of neural stem cells.

    • Intermediate Zone and Marginal Zone:

      • Pathways for migrating cells to encounter different microenvironments, facilitating differentiation into various neural cell types.

Neocortex and Cortical Development

  • Focus on the structure of the cerebral cortex (also known as neocortex):

    • Differentiation into specific layers during development.

    • Layers have distinct cell types and functional roles in processing sensory inputs.

Radial Layers of the Cortex

  • Layer Functions:

    • Different layers connect with different brain regions and have specific input/output relationships (e.g., Layer 4 receives input from thalamus, Layer 6 sends output).

  • Layer Stratification:

    • Established by transcription factors like LHX2, critical for normal cortical organization.

    • Knockout experiments demonstrate LHX2's role in maintaining cortical layering.

Stem Cell Dynamics

  • Neurogenesis:

    • The creation of new neurons from stem cells.

  • Cell Migration:

    • Newly formed neurons migrate away from the ventricular zone to their final cortical layers.

  • Differentiation:

    • Stem cells transition into specialized neural cells based on environmental signals they encounter.

Pathways of Ventricular Radial Glia

  • Functions of Radial Glia:

    • Serve as a scaffold for migrating neurons.

    • Capable of asymmetric division to create both stem cells and differentiated neurons.

Role of Reelin in Migration

  • Reelin:

    • A signaling molecule aiding neuronal migration by stabilizing cytoskeletal dynamics in response to varying concentrations.

  • DAB1 Receptor Functionality:

    • Essential for relin’s migration-promoting effects; loss of DAB1 affects migration outcomes.

Axon Navigation

  • New neurons must establish connections with distant targets through axon navigation or pathfinding.

    • Growth Cone Functionality:

      • The growth cone guides axon extension and is responsive to environmental cues.

  • Cues in Axon Navigation:

    • Long-range cues: Chemoattractants (e.g., netrins) attract axons, whereas chemorepellants (e.g., slits) prevent undesired movement.

    • Short-range cues: Cadherins and other factors that guide nearby axons.

Conclusion and Summary

  • Axon pathfinding involves a balance of attractive and repulsive cues to ensure proper synaptic connections are made while avoiding retracing of paths.

  • Understanding these processes is crucial for insights into brain development and potential therapeutic interventions for neurological disorders.