Parallel arrangement of capacitor and resistor in leaky integrate-and-fire model I have read from several sources that in the leaky integrate-and-fire model of a single neuron resistor (leakage) and capacitor (membrane potential) are arranged in parallel. Look at the following RC circuit, taken from the book Neuronal Dynamics:



The author says:


  The cell membrane acts like a capacitor in parallel with a resistor
  which is in line with a battery of potential $u_{rest}$.


But I think capacitor and resistor are arranged in series. Can anybody please explain why it is said that they are arranged in parallel?
I see your confusion is caused by $u_{rest}$. Indeed that diagram is somewhat confusing because $u_{rest}$ is not the main source relative to which to consider the topology of the circuit. The main source is actually a current source designated by $I(t)$ in your diagram. With respect to that source R and C are in parallel. If that's not convincing enough, consider another (information) source which presents a different (but still leaky) integrate and fire model, sans a $u_{rest}$: 



In the latter diagram, $I_{dc}$ is the equivalent of $I(t)$ in yours. In the alternative circuit, the firing actually comes from a voltage-controlled switch, which is indeed in series with the RC circuit (to the left of it).