Lecture 17: Influences on Axon Growth

TL;DR

Axons compete for growth factors and are guided by chemical cues in their growth, with experiments showing the role of NGF and neurotrophins in directing axon growth.

Transcript

GERALD SCHNEIDER: So we're going to continue some factors. We're going to continue the discussion of external growth today, talk a little more about what's guiding those axons when they're growing. We talked about the two modes of growth last time, so you know a little bit about how they develop. There's many different aspects to the idea of axons ... Read More

Key Insights

• 🧑‍🏭 Axons compete for growth factors and need them for survival and growth.
• 🖐️ NGF and neurotrophins play important roles in promoting axon growth and guiding its direction.
• ⛑️ Chemical cues, like NGF, can directly influence the direction of axon growth.
• ❓ The chemoaffinity theory proposed by Roger Sperry has been supported by experiments and explains the specificity and development of axon connections.
• 🛀 Lesions and experiments have shown the violation of neuron specificity rules and the potential for axons to sprout and project into different regions.
• 🛀 Additional experiments have shown the role of specific glial cells as guideposts and barriers to axon elongation.

Questions & Answers

Q: What happens if axons don't receive enough growth factor?

If axons don't receive enough growth factor, they can undergo apoptosis or cell death.

Q: What is the role of NGF and neurotrophins in axon growth?

NGF and neurotrophins promote axon growth and also influence the direction of axon growth.

Q: How was it shown that NGF can directly influence the direction of axon growth?

An experiment with a pipette containing NGF showed that axons would grow towards the location where the NGF was leaking, demonstrating the ionotropic effect of NGF.

Q: What did Ramon y Cajal and Roger Sperry propose in relation to axon growth?

Ramon y Cajal postulated chemical effects on axon growth, while Roger Sperry developed the theory of chemoaffinity, suggesting that axons are guided by chemical cues in their growth.

Summary & Key Takeaways

• Axons compete for growth factors, and if they don't receive enough, they can undergo apoptosis or cell death.

• Nerve Growth Factor (NGF) and neurotrophins are important growth factors that play a role in promoting axon growth and influencing its direction.

• Experiments have shown that NGF can directly influence the direction of axon growth and guide axons to specific areas.