In axons the cytoskeletal polymers are transported by slow axonal transport. Microtubules, microfilaments and neurofilaments move at different rates in the axon. On the basis of their transport rates, two populations of polymers can be distinguished: SCb polymers are transported at 2–4 mm day−1 and SCa polymers are transported at 0.25–1 mm day−1. As they move within the axon, the faster moving SCb polymers must pass the slower moving SCa polymers. This observation and others indicate that polymers slide in the axon. A model of polymer sliding is presented. This model provides a dynamic architectural framework for studies of the mechanisms of slow axonal transport.
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