This is a phantom bursting model, (see Bertram et al, Biophys. J. 79:2880-2892, 2000 ) for pancreatic beta-cells in which the role of s_1 is played by cytosolic calcium (c) and the role of s_2 is played by ER calcium (cer) and the ADP/ATP ratio (a).
Reference: Bertram and Sherman, Bull. Math. Biol., 66:1313-1344 2004.
The best way to see the animations is with XPP and its animator.
With these files you can view the moving slow manifold and nullcline in the V-w (omega) plane. The file is set to produce slow bursting with the ER/ATP model. To see animation choose View/Toons and read in the animation file from the animator File menu. File/Get set can be used to visualize other burst modes. You will need to adjust the parameters ttotal, wmin, and wmax to get the right scaling.
Warning: Some of these files are large, so make sure you have enough free memory (256 - 512 MB recommended). I recommend downloading the image file to your machine and playing there (eg., in Netscape right-click)
What you will see: Each animation has the time course in purple in the upper half and the v-w phaseplane in the lower half. The slow manifold (where v and n are at steady state) is in black and the w nullcline is in blue. The trajectory is red.
In these fast bursts the slow manifold and w nullcline are stationary or very nearly so.
(The rest of the files are large (up to 2 MB), and they will use much more memory than that when rendered, so they are plotted sparsely and split into Silent_to_Active and Active_to_Silent transitions.)
In the ER model the w nullcline oscillates. The movement is subtle so look closely.
In the ER/ATP model both the slow manifold and the w nullcline oscillate.