Fig. 5.

Three-dimensional reconstruction of the dendritic filopodium whose origin is shown in Figure 2. The filopodium is ∼11 μm long from origin to tip. Filopodia of this length were rarely captured in series of only 100 ultrathin sections. At its narrowest point (solid arrow) the filopodium has a diameter of ∼0.1 μm, whereas the maximum diameter is ∼1 μm. The filopodium is enfolded in stubby protrusions from the axon, one of which (star) appears to make a synaptic contact with the filopodium (F) (inset, star arrow). Scale bar in inset, 0.5 μm; 3D scale bar, 1 μm.