Some neurology texts classify cogwheeling as a variation of tremor, with the manifestation visible upon testing - either by wrist rotating or flexion of the arm. Evidence for this comes from that fact that cogwheeling can be seen in tremors without muscle tone increase.
Essential tremor, for example, demonstrates this finding.
If you approach these symptoms (dystonia, cogwheeling) from a Parkinson's perspective, it becomes more evident that this is a phenomena associated with a drop in intracerebral dopamine (<50% of normal). Subsequent mismatch of dopamine/cholinergic activity then contributes to symptoms.
The pathophysiology (stretch receptors, golgi tendon organs, etc, flower spray, annulospiral end organs) of the various symptoms are difficult to ascertain due to the differences in anatomic distrubition and individual differences in postsynaptic receptors for dopamine (of which there are 4 types).