Fig. 13.

Possible mechanisms by which filopodia might induce shaft synapses. A, Synapses form on the receptive surface of filopodia, but only those near the base of filopodia are stabilized into shaft synapses. B, Filopodia retract, pulling the presynaptic partner to the dendrite. C, Dendritic filopodia guide axonal filopodia to the dendrite where synapses are stabilized by subsequent maturation of the axonal filopodium into an axon branch. D, Dendritic filopodia act as conduits along which synapses move to the dendrite shaft.