Figure 1. Equivalent electrical circuit of a short segment of the muscular wall of the gastric antrum.

A, a schematic representation of a small segment of antral wall comprising a layer of circular smooth muscle, which includes some ICC_IM, connected via a resistive pathway (R_C-IC) to the ICC_my layer. On the right of the panel, a layer of longitudinal smooth muscle is also connected to the ICC_my layer via a resistive pathway (R_L-IC). B, the equivalent electrical circuit describing current injection (I) into a circular muscle cell. Shown are equivalent resistors for the circular layer (R_C), the ICC_my layer (R_ICC) and the longitudinal layer (R_L). Access resistances connecting the ICC_my to the muscle layers are shown as R_C-IC to the circular muscle layer and R_L-IC, to the longitudinal muscle layer. Steady-state voltages arising in response to current injection, V₁, V₂ and V₃, are marked at the circular, ICC_my and longitudinal layers. Also shown are pacemaking elements, R_{ICC-Pacemaker} and E_Pacemaker, but these are disconnected to simulate baseline conditions; their connecting switch is shown open. C, the equivalent circuit describing the state during spontaneous depolarization of the ICC_my layer in the absence of current injection. In this case, depolarization (V₅) occurs because the switch is closed, mimicking the peak of a pacemaker potential. R_{ICC-Pacemaker} represents the increase in ICC_my membrane conductance that provides the pacemaker current shunt, and E_Pacemaker represents the equilibrium potential for the pacemaker current.