Structure of the cytoskeleton in neuronal processes of DIV7 hippocampal neurons. (A) PREM of a portion of the neuron with dendrites (e.g., box d) and an axon (box b) extending from the soma (bottom left). The axon forms a loop, so that proximal and distal segments can be seen next to each other (box b). (B and C) Sequential enlargements of box b in A showing exposed MTs with occasional thin fibrils (arrows) in the distal axon (bottom segment) and a fibrillar coat over MTs (arrowheads) in the proximal axon (top segment). (D and E) Sequential enlargements of box d in A showing dendrite cytoskeleton that lacks a fibrillar coat. Bars: (A) 10 µm; (B and D) 2 µm; (C and E) 200 nm.