An artificial pacemaker provides an electrical stimulus to bring cardiac muscle cells to threshold and initiate action potentials when the pacemaker cells in the heart are not working properly....

An artificial pacemaker provides an electrical stimulus to bring cardiac muscle cells to threshold and initiate action potentials when the pacemaker cells in the heart are not working properly. Suppose that the pacemaker provides a current applied as a square-wave pulse (consider it to be a step input, as you are only interested in the sudden increase in current). The cell membrane can be modeled as a resistor and capacitor in parallel, as shown in Figure 5.76.You want to bring the membrane potential up from -90mV to the threshold value of -55mV (after which the Na+ channels open and the action potential begins), so you need to apply a voltage of 35 mV. The value of the membrane resistance is 3300Ω and the membrane capacitance is 1.5mF. If you want the increase in voltage to occur within 5 ms, what should be the value of the applied current (i_m)?