MATLAB, How to filter a discrete signal?
Easiest way to remove baseline is to remove the average:

filtered = original - mean(original);


Actually, the average is the first coefficient of the Fourier transform, so it is actually a very sharp filtering: you are eliminating the DC coefficient.

If you want more classic filtering, then check functions like butter and friends, which will synthesize an IIR filter, then use filter to filter out your signal.

Matlab also includes a filter design tool.