Channel proteins is the answer to your question
Each layer of earth has a different density the more in you go with the layers the more density is going to show up.
Crust-2.2g/cm^3
Upper mantle-3.4g/cm^3
Lower mantle-4.4g/cm^3
Outer core-9.9g/cm^3
Inner core-12.8g/cm^3
Hope I helped in something, Sorry if I didn't gave it my best shot:)
Answer:
The areas that have had the action potential are refractory to a new action potential.
Explanation:
Hope this helps<3
