Explain how the resting potential of -70mV is maintained in a sensory neuron.

The resting potential is a result of the concentrations of the sodium and potassium ions inside the neuron compared to outside. The leaky channels in the sensory neuron membrane allow the movement of Na+ (sodium ions) and K+ (potassium ions) to move across the cell membrane via diffusion, i.e. down their concentration gradient. In addition, three sodium ions move out of the membrane for every two potassium ions that move into the membrane via the sodium potassium pump.
The combination of the sodium-potassium pump and the leaky channels results in the cell maintaining a stable, negative, resting membrane potential.