Protein 5. Enzymes 6. Cell Respiration 9. Photosynthesis 3: Genetics 1. Genes 2. Chromosomes 3. Meiosis 4. Inheritance 5. Genetic Modification 4: Ecology 1. Energy Flow 3. Carbon Cycling 4. Climate Change 5: Evolution 1. Evolution Evidence 2. Natural Selection 3. Classification 4. Cladistics 6: Human Physiology 1.
Digestion 2. In humans this is said to be around mV [2]. This means that the inside of the cell is negatively charged in comparison to the outside.
Resting membrane potentials are maintained by two different types of ion channels: the sodium-potassium pump and the sodium and potassium leak channels. Firstly, there is a higher concentration of the potassium ions inside the cell in comparison to the outside of the cell. This creates an unequal distribution of potassium ions, or more accurately, a potassium ion gradient is created.
Therefore, following the concentration gradient, the potassium ions will diffuse from the inside of the cell to outside of the cell via its leaky channels. As the potassium ions leave the cell, it increases the number of anions trapped inside the cell, hence accumulating the negative charges and the positive charges are accumulated outside of the cell.
The resting membrane potential is determined mainly by two factors: the differences in ion concentration of the intracellular and extracellular fluids and the relative permeabilities of the plasma membrane to different ion species. Sodium, potassium, and chloride ions are present in the highest concentrations and therefore generally play the most important roles in the generation of the resting membrane potential. These concentration differences for sodium and potassium are due to the action of a membrane active transport system which pumps sodium out of the cell and potassium into it.
The pump protein is phosphorylated by ATP. To understand how the concentration differences for sodium and potassium maintained by the membrane pumps create membrane potentials, let us consider the following situation: let us assume that the membrane is permeable only to potassium but not to sodium.
Therefore, potassium can diffuse through the membrane but sodium cannot. Initially there is no potential difference across the membrane because the two solutions are electrically neutral; i.
There is also a concentration gradient favouring sodium diffusion in the opposite direction but the membrane is not permeable to sodium. Accordingly, after a few potassium ions have moved out of the cell, the cell will have an excess of negative charge, whereas the outside solution will have an excess of positive charge; i.
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