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Cytoskeleton, microtubules & filaments, axon, x-section.
Filaments are usually inconspicuous and vary in thickness and arrange-ment; some attach to desmosmes and zonulae occludens; others function in cell movement.
Tubules have a dense wall and clear center. They are composed of protein subunits and are found in most cells, but always form the spindle in mitosis.