1. The problem statement, all variables and given/known data Derive the differential equation that relates the voltage (V) to the current (I) entering the circuit. 2. Relevant equations Let: ic = C dV/dt = current traveling through the capacitor (C) ik = (V+Ek) / Rk = current traveling through the potassium (K) channel iNa = (V-ENa) / RNa = current traveling through the sodium (Na) channel iCl = (V+ECl) / RCl = current traveling thought the chlorine (Cl) channel I = ic + ik + iNa + iCl = total current 3. The attempt at a solution I = ic + ik + iNa + iCl I = C dV/dt + (V+Ek) / Rk + (V-ENa) / RNa + (V+ECl) / RCl My confusion is from the signs of the batteries. What is the convention (or physical meaning) when you are subtracting the voltages. For example, in the potassium (K) channel, it is V - (-Ek); while in the sodium (Na) channel, the signs on the battery are reversed. How do I know when a voltage source is positive or negative in relation to the current flow? Thank you!