What are the two forces that go into how ions move across membranes?

 It turns out that you can measure the charge difference across the membrane. (In other words, you can find out how different the charge inside vs outside is). This difference is measured as a voltage (units = mV).

 

If we only had the Na+/K+ pump involved, the charge difference of the cell = -0.5mV. But when we measure a real neuron, we find a charge difference of -70mV! This is way more negative than we expect and it means we don't have all the information regarding a cell at rest.

 

Please watch two videos next to better understand what else is going on. First, you'll learn about electrochemical gradients and then you'll review the whole picture of a cell at rest.

Watch and Review electrochemical gradients videoLinks to an external site. (6 minutes)

What are the two forces that go into how ions move across membranes?

•   physical (mechanical) force 
•   THE FORCE (like what Yoda uses) 

•   electrical force (+ vs - charges) 
•   chemical force (concentration gradients) 
•   ATP