Resting potential is the voltage difference across a cell membrane, maintained by protein ion channels and pumps. Neurons and muscle cells use it to effect changes. Sodium and potassium ions are involved in creating and maintaining the resting voltage. Calcium ions are important in maintaining the resting membrane potential in muscle cells.
The resting potential is the voltage difference across a cell membrane, and is sometimes referred to as the resting voltage. Some cell types, such as neurons and muscle cells, use the resting potential to effect changes within the cell and within the body. Action potentials, muscle contraction, and the establishment or change of equilibrium processes in the cell all involve the resting membrane potential.
There are different concentrations of ions in the cytosol, or within the cell, as well as within different cellular compartments and organelles. Since the ions are either positively or negatively charged, they create a difference in charge between these different compartments, forming an electrical potential difference. Often, cells will want to maintain this difference across a membrane using protein ion channels and pumps. When an electric potential difference is maintained, it is referred to as the resting potential.
The ions most involved in creating and maintaining a resting voltage for a membrane are sodium (Na) and potassium (K) ions. Generally, the concentration of K+ is higher inside the cell than outside, while the concentration of Na+ is higher outside the cell than inside. This difference is maintained by a membrane protein pump called Na+/K+-ATPase, which uses adenosine triphosphate (ATP) as energy to maintain relative concentrations. The pump incorporates three Na+ ions into the cell for every two K+ ions it exports, imparting a more negative charge inside the cell. This resting potential is especially important for neurons, which use the voltage difference to fire action potentials.
In neurons and other cells of the nervous system, an action potential is generated when the resting potential is disturbed. The action potential begins with an influx of Na+ ions into the cell through certain ion channels, which creates a depolarization of the membrane potential once it reaches a certain threshold. Here the action potential is generated and the electrical signal is transmitted through the neuron. After the Na+ surge, more voltage-gated ion channels open, releasing K+ from the cell, a step in the action potential known as hyperpolarization, in which the membrane potential falls below the normal resting voltage. The cell then re-establishes its resting potential by using Na+/K+-ATPase in the repolarization process.
Calcium ions (Ca) are also important in maintaining the resting membrane potential in muscle cells. Ca2+ ions are stored in an organelle called the sarcoplasmic reticulum, which contains protein pumps to maintain high Ca2+ concentrations within the compartment. When a muscle cell is told to contract, an electrical signal activates the sarcoplasmic reticulum using the resting potential. The compartment is then able to open, releasing Ca2+ ions into the cell, which bind to the fibers allowing the muscle to contract.
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