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# Biology Grade 12 ## Unit 5: Human body system ### Figure 5.4. Resting potential ### Polarization * In the resting state the inside of the membrane has a negative electrical potential compared to the outside. This difference in potential is called resting potential (about -40mv to -90mv). * The i...

# Biology Grade 12 ## Unit 5: Human body system ### Figure 5.4. Resting potential ### Polarization * In the resting state the inside of the membrane has a negative electrical potential compared to the outside. This difference in potential is called resting potential (about -40mv to -90mv). * The interstitial fluid has a high concentration of $Na^+$ which is about 16 times higher outside the neuron than inside the neuron. Similarly, the axoplasm has a high concentration of $K^+$ which is about 25 times higher inside than in outer interstitial fluids. * Due to the difference in Na, K concentration, the $Na^+$ ions diffuse inside the exoplasm, and $K^+$ ions tend to diffuse outside of it. * The membrane of the neuron at resting is more permeable to $K^+$ ion than $Na^+$ ion. So, $K^+$ leaves the neuron faster than $Na^+$ enters the neuron. * $Na^+$ and $K^+$ are transported across the membrane against their concentration gradient by carrier protein, which is called Na-K pump and energy is used through ATP. * The difference in permeability results in accumulation of high concentration of cation (+ve charged ion) outside of the neuron compared to the concentration of cation inside. * Sodium channels are opened, but potassium channels are closed and