Mt treadmilling occurs as the result of different ccs between the + and - end of a mt. in general, the + end of a mt has a cc that is less than that of the - end. treadmilling occurs when the local alpha-beta tubulin dimer concentration falls between the two critical concentrations of a mt, thus resulting in shrinkage of the - end and growth of the + end. if you focus on one particular tubulin dimer subunit in the middle of the mt, the mt will appear to move like a treadmill as that particular subunit gets nearer and nearer to the - end (because the - end is shrinking). see diagram in slides.
