Fig. 1.

Mechanisms of axon guidance. Growth cones, the motile tip of a growing axon, integrate four major categories of guidance information [3]. a, b Long range chemoattractants (a) or chemorepellents (b) that act at a distance to orient the growth cone either towards or away from the signal. c, d Contact mediated chemoattractants (c) or chemorepellents (d) that orient axons through direct contact with the growth cone