The geometry of the half-sarcomere as used in the model. A. The cylindrical geometry formed by rotating the plane in B. B. Roman numerals denote regions where different model equations are used. I: homogenised region, II: cytosol in the non-homogenised region, III: SR in the non-homogenised region. Lowercase letters denote the boundaries. a: L-type channels, b: NCX, SL pump and background flux, c: RyR, d: SERCA pump, e: Homogenised/non-homogenised cytosolic boundary, f: Homogenised/non-homogenised SR boundary. The numbered points show where readings of calcium concentration were taken (see Results).