Survival of the Fittest Neurons! 💪⚔️
⚔️ Cell Competition: The Battle!
- Limited Resources 🎯: Not enough NGF and tropic factors for all neurons!
- Limited Sites 📍: Few locations available for millions of neurons!
- Winner Takes All 💪: Only strongest neurons survive!
- 40x More Cells! ✖️40: Early brain has way more than adult brain!
💀 Why Neurons Die
- No Connections 🔗❌: Can't form synapses = Death!
- No Projections 🌿❌: Arrive but don't send out axons/dendrites = Death!
- Can't Compete ⚔️❌: Lose postsynaptic space battle = Death!
- Wrong NGF Levels ⚖️: Too much or too little = Death!
🔄 Synaptic Rearrangement
- Cells sprout MANY connections first 🔗🔗🔗
- Then refined and made precise! ✨
- Weak connections die off 💀
- Efficient system remains! ⚡💪
🧬 Three Migration Hypotheses
1️⃣ Chemoaffinity Hypothesis (Sperry) 🧪
- Theory: Chemicals attract axons to targets! 🎯
- Evidence: Frog eye rotation experiments 🐸🔄
- Problem: Can't explain extra limbs or roundabout routes! ❌
2️⃣ Blueprint Hypothesis 📋
- Theory: Pioneer growth cones lay pathways! 🌟
- Evidence: Following neurons get lost if pioneers destroyed! 😵
- Problem: Can't explain in vitro travels! 🧫❌
3️⃣ Topographic Gradient Hypothesis 🗺️
- Theory: Neurons maintain point-to-point relationships! 🔗
- Evidence: Retina-tectum connections maintain positions! 👁️🧠
- Strongest evidence! 💪✅
🔑 Key Takeaways
- Neurons compete fiercely for survival! ⚔️💪
- Cell death is normal and necessary! 💀✅
- Connections determine survival! 🔗
- Multiple mechanisms guide migration! 🗺️
- Self-regulation controls development! 🎯
- The mystery continues! 🧩🔬