How does mass spectroscopy of nicotine work? Take this nicotine molecule:



And this mass spectrum:



I'm not sure how to explain all the peaks.

This might explain the peak at 42:

 

But can this peek als be explained by something else in the molecule? 

Like the decomposition of the ring with the double bonds:


This might explain the peak at 84: 



And I'm clueless on the peak at 133
The peak at 133 corresponds to a loss of 29 mass units (nicotine is 162).  N-CH3 has a mass of 29