MID 3-AXONS

axon initiation part 1

neurite of post mitotic neuron adjacent to basal lamina signaled to become an axon

axon initiation part 2

as layers form in neural tube, morphogens signal axon to exit neural tube

how do processes grow?

axon growth cone

tip of axon differentiated into

autonomous growth cone

• cytoplasmic ‘suitcase’: cone loaded with everything needed for protein synthesis

  • cytoplasmic proteins

  • actin molecules

  • microtubules

axon growth cone enables…

axon survival, elongation and navigation proteins

axon growth cone emancipates….

growth cone from having to wait for proteins formed in soma

filipodia of growth cone…

constantly pull and cause axon to elongate

growth cone behavior dependent on…

which signals filipodia encounter

type of signals filipodia can encounter

1. attract/adhesion molecules ‘advance’

• ex. cell adhesion molecules (CAMs)

2. repellent molecules ‘retreat’

3. physical/mechanical barriers ‘go around’

• ex. ‘stiff’ cells (e.g. cells with collagen)

pioneer axons

1st axons to exit neural tube or grow into a new region

• hyper active growth cones

pioneer axons follow…

regional signals and forge pathway to correct target tissue

pioneer axons produce…

region specific CAMs and incorporate into axon membrane along the way

• attract and guide follower axons

• cause follower axons to adhere