🔑 Key Definitions
Cell Competition: Process where developing neurons compete for limited trophic factors and synaptic space
Synaptic Rearrangement: Refinement process where weak connections are eliminated and strong connections are strengthened
Radial Glial Cells: Specialized glial cells that guide migrating neurons along their processes during development
Chemoaffinity Hypothesis: Sperry's theory that neurons find targets through specific chemical labels
Synaptic Rearrangement: Refinement process where weak connections are eliminated and strong connections are strengthened
Radial Glial Cells: Specialized glial cells that guide migrating neurons along their processes during development
Chemoaffinity Hypothesis: Sperry's theory that neurons find targets through specific chemical labels
👤 Important Figures
- Roger Sperry - Developed chemoaffinity hypothesis; demonstrated specific neural connections through eye rotation experiments
🧠 Three Hypotheses of Neural Connection
- Chemoaffinity Hypothesis (Sperry): Neurons have specific chemical markers that allow them to recognize and connect with appropriate targets
- Blueprint Hypothesis (Pioneer Axons): First axons to reach a target establish pathways for later-arriving neurons to follow
- Topographic Gradient Hypothesis: Neurons form ordered maps through gradients of chemical signals across target tissues
📊 Key Developmental Processes
- Cell Death: Approximately 50% of neurons die during development; those that secure trophic support survive
- NGF Importance: First identified trophic factor; neurons that don't receive adequate NGF undergo apoptosis
- Synaptic Rearrangement: Initially overproduced synapses are pruned based on activity and functionality
- Radial Glial Guidance: Provides scaffold for neuron migration from ventricular zone to cortex
💡 Exam Tips
- Remember Sperry's chemoaffinity - neurons have "chemical addresses"
- Know that ~50% of neurons die during normal development (not a pathology)
- NGF was the first trophic factor discovered - set the precedent
- Distinguish three hypotheses: chemoaffinity (labels), blueprint (pioneers), topographic (gradients)
- Radial glia guide migration but don't determine final connections
- Cell death is activity-dependent and target-dependent