Lecture 12

How Growth Cone moves: Labeled pathway hypothesis

Chemical cues. Respond to attractive/repulsive molecules.

Cell surface receptors - cues in the environment, tell neuron where to go (changes internal skeleton): attractive molecules

Cell surface receptors: repulsive molecules

Layout pathway hypothesis

Layout of attractive and repulsive molecules in brain and body forms a labeled pathway that growth cones will follow.

Axon Development

Test for labeled hypothesis

Adding a third eye anywhere in the head - growth of axons to the correct location.

Guided by diffusible chemoatractants that form a concentration gradient to attract growing axons.

So what do mammals use?

BOTH: chemoattractants AND labeled pathways; in spinal cord:

Initial part - chemoattractants grow axons from commissural interneurons to floor plates.

After midline, axons turn and join bundle

Overview

Formation of specfiic connections during neural development.

Origin of neurons,axon pathfinding

Refinement of synaptic connecections

Refinement of synaptic connections

Upon Arrival

When motor axons arrive at their targets, they form far too many synapses

Ex. muscle fibers; they go thru process of synapsis elimination

Hebbs Rule

If a cell a is successful in getting a target cell b to fire, then the connection is strengthened, and vise versa.