The «parts list» in these processes is similar: Microtubules, semi-rigid tubes of protein, can serve within the cell as scaffolding, roadways, and a building material for machinery; some proteins serve as fasteners, binding and releasing other materials; and motor proteins use chemical energy to push and pull
materials along microtubules, or move the microtubules themselves.
This interrupts the transport of cellular
materials along axonal
microtubules, causing these
materials to accumulate at several points
along the axon where they may give rise to varicosities.