All life originates from the sea. Therefore, there are conditions in the body that build on these original conditions of life. This means that vital building blocks in the organism are salts. They enable all physiological processes, are part of the organs and form ions in aqueous solution. Sodium and potassium chloride are dominant salts in cells. In ionic form, they drive protein functions, determine the osmotically active components between cell interior and external conditions, and cause electrical potentials. One such potential is the membrane potential.
What is the membrane potential?
A membrane potential is the electrical voltage or potential difference between the outside and inside of a cell membrane. All cells have the property of forming a membrane potential. A membrane potential is understood to be the electrical voltage or potential difference between the outside and the inside of a cell membrane. When concentrated electrolyte solutions of a membrane are separated from each other and there is conductivity in the membrane for ions, a membrane potential occurs. Biological processes in the body are extremely complex. Especially for muscle and nerve cells, and also for all sensory cells, the membrane potential plays a decisive role. In all these cells, the process is in a state of rest. Only by a certain stimulus or excitation the cells are activated and a change of voltage occurs. The change occurs from the resting potential and returns to it. In this case we speak of depolarization. This is the decrease of membrane potential due to electrical, chemical or mechanical effects. The voltage change takes place as an impulse and is transmitted along the membrane, thus transmitting information throughout the organism and making it possible for the individual organs to communicate with each other, the nervous system, and the environment.
Function and task
The cell in the human body is excitable and consists of sodium ions, insofar as they are extracellular. Few sodium ions are present intracellularly. The imbalance between the inside and outside of the cell results in a negative membrane potential. Membrane potentials are always negatively charged and have constant and characteristic magnitudes in individual cell types. They are measured with microelectrodes, one leading into the interior of the cell and the other being located in the extracellular space as a reference electrode. The cause of a membrane potential is the difference in concentration of ions. This means that electrical voltage builds up across the membrane, even if the net distribution of positive and negative ions is the same on both sides. A membrane potential builds up because the lipid layer of the cell makes it possible for ions to accumulate on the membrane surface, but they cannot penetrate through nonpolar regions. The cell membrane has too low a conductivity for the ions to do so. This results in a high diffusion pressure. Not only as a whole, each individual cell has electrical conductivity. The diffusion pressure then leads to transfer from the cytoplasm. As soon as a potassium ion escapes under these conditions, positive charge is lost in the cell. Therefore, as a consequence, the inner membrane surface becomes negatively charged to create a balance. Thus an electrical potential is formed. This increases with each change of sides of the ions. In turn, the concentration gradient of the membrane decreases, and with it the diffusion pressure of the potassium. The outflow is thus interrupted and a new equilibrium is created. The level of a membrane potential differs from cell to cell. As a rule, it is negative with respect to the cell exterior and varies in magnitude from (-)50 mV to (-)100 mV. In smooth muscle cells, on the other hand, smaller membrane potentials of (-)30 mV develop. As soon as the cell expands, which is the case in muscle and nerve cells, the membrane potential also differs spatially. There it serves primarily as propagation and signal transmission, while in sensory cells it enables information processing. The latter occurs in the same form in the central nervous system. In the mitochondria and chloroplasts, the membrane potential is the energetic coupling between the energy metabolic processes. In this process, ions are transported against the voltage.Under such conditions, measurement is difficult, especially if it is to take place without mechanical, chemical or electrical interference. Other ratios occur in the cell exterior, i.e. in the extracellular fluid. There are no protein molecules there, which is why the ratio is reversed. Although the protein molecules have a high conductivity, they cannot pass through the membrane wall. Positive potassium ions always strive to balance the concentration. Therefore, a passive transport of the molecules in the extracellular fluid occurs. This process continues until the built up electrical charge is in equilibrium again. In this case, a Nernst potential occurs. This states that a potential can be calculated for all ions, since the magnitude depends on the concentration gradient on both sides of the membrane. For potassium, the magnitude under physiological conditions is (-)70 to (-)90 mV, and for sodium it is about (+)60 mV.
Diseases and disorders
The magnitude of the membrane potential characterizes the general health of the cells. A healthy cell has the magnitude of (-)70 to (-)90 mV. The energy flow is strong, and the cell is highly polarized. Fifty percent of the subtle energy is used for polarization. Accordingly, the membrane potential is high. In a diseased cell, the situation is different. It needs fine-material energy from its environment by the energy-poor area. In doing so, it either performs a horizontal oscillation or a left turn. The membrane potential of these cells is very low, as is the cell vibration. Cancer cells, for example, only have a magnitude of (-)10 mV. The susceptibility to infection is therefore very high.
