10/20 Notes

Discusses how neurons establish their connections through processes such as:
- Neuronal Migration: The movement of neurons from their birthplace to their final location in the nervous system.
- Pathfinding: The process by which growing axons navigate through the nervous system to reach their target cells.
- Dendritogenesis and Axon Morphogenesis: Refers to the development of dendrites and the shape/form of axons during neuronal growth.

Neurons form specific connections with particular targets, exemplified within the visual system:
- Retinal Targets: Coordination of visual pathways connecting the retina with various brain regions (e.g., Lateral Geniculate Nucleus, Striate Cortex, etc.).
- Illustrative Features: Includes diagrams and landmarks such as the Optic Nerve, Optic Chiasm, and various nuclei in relation to visual processing.

The visual system pathways and their relationship to different neuronal targets are illustrated with figures and examples highlighting rostral and ventral connectivity.

The axonal journey is divided into manageable segments, showing each step that an axon takes to reach its target:
1. Crossing the Optic Chiasm: Axons from the nasal retina cross over to the opposite side to reach their target.
2. Extension through the Optic Tract: Importance of correct directional growth toward appropriate brain regions.
3. Targeting: Accurate navigation to specific regions (e.g., Optic Tectum, Lateral Geniculate Nucleus).
Analogy: The growth of an axon compared to a driver navigating through streets, illustrating the complexity and challenges faced during pathfinding.

Definition: Specialized structures at the tips of axons that play a crucial role in guiding axon growth and target selection.
Components of Growth Cones:
- Actin Bundles: Found in the filopodia, involved in sensing the extracellular environment.
- Microtubules: Provide structure and facilitate the transport of materials to the growth cone.
Historical Observations: Key developmental insight from researchers like Ramón y Cajal and others on the structure and behavior of growth cones.

Adhesion Molecules:
- Different types including Cadherins, Integrins, and various Cell Adhesion Molecules (CAMs).
- Cadherins: Calcium-dependent adhesion molecules that help in neuron-neuron interactions.
- Integrins: Composed of multiple subunits, these molecules interact with the extracellular matrix (ECM) to facilitate adhesion during axon guidance.

Definition: The process by which growing axons adhere to one another, forming bundles known as fascicles.
Significance: Facilitates the cooperative growth of axons that share similar trajectories.

Different guidance cues influence axon pathfinding, categorized into:
- Long-range Cues: These include (Semaphorins) and (Netrins) which assist in directing growth over greater distances.
- Short-range Cues: Such as (Eph ligands) and extracellular matrix components (ECM) which provide localized signals.
Known Guidance Cues and their receptors include:
- Netrin/DCC, Ephrin A/EphA, and others that mediate attractive or repulsive signals during axon guidance.

Description: Experiments that demonstrate how growth cones respond to chemical gradients, moving towards or away from stimuli, further illustrating the principle of chemotaxis in axon guidance.

General Property: The release of neurotransmitters is a common function across various growth cones.
Notable Neurotransmitters: Include ACh (Acetylcholine) and GABA (Gamma-Aminobutyric Acid), highlighting their roles in neuronal signaling and pathfinding.