Systems Biology
Resting membrane potential is a cell's baseline charge, referring to the difference in charge between the inside and the outside of a cell when it is not undergoing an action potential. For neurons, the resting membrane potential is around -70 millivolts, indicating that the inside of the cell is 70 millivolts more negative relative to the outside. This charge is generated by ions accumulating inside the cell and in the extracellular space. Key ions involved in resting membrane potential are sodium and potassium. At rest, sodium is more concentrated outside the cell, whereas potassium ions are more concentrated inside the cell. This creates concentration gradients for each ion, driving the flow of sodium and potassium ions through leaky channels in the membrane.
Equilibrium potential is the charge across the membrane when the inward and outward flows of an ion balance each other out. Since there are multiple ions in play, a neuron's actual resting membrane potential lies between the equilibrium potentials of the key ions but closer to potassium's equilibrium potential. This is due to the cell membrane being leakier to potassium ions, allowing them to have a stronger pull in determining resting membrane potential. Resting membrane potential relies on ion concentration gradients, maintained by the sodium-potassium ATPase pump. Using active transport through ATP, the pump exchanges three sodium ions out of the cell for two potassium ions brought in, maintaining the sodium and potassium ion concentration gradients across the membrane.
Lesson Outline
<ul> <li>Introduction to Resting Membrane Potential</li> <ul> <li>Inside of cell (neuron) vs outside of cell (extracellular space)</li> <li>Resting membrane potential: around -70 millivolts (mV)</li> </ul> <li>Key ions: Sodium and Potassium</li> <ul> <li>Sodium concentration higher outside cell, potassium concentration higher inside cell</li> <li>Concentration gradients drive ion flow through leaky channels</li> </ul> <li>Electric gradients</li> <ul> <li>Generated by ions crossing membrane; it can push against concentration gradients</li> <li>Potassium electric gradient drives potassium ions back in</li> </ul> <li>Equilibrium potential</li> <ul> <li>Where inward and outward flows balance each other out</li> <li>Potassium equilibrium potential: -90 millivolts</li> <li>Sodium equilibrium potential: +65 millivolts</li> </ul> <li>Role of other ions</li> <ul> <li>Chloride ions high concentration outside cell</li> <li>Equilibrium potential similar to resting potential, role reinforced under most circumstances</li> </ul> <li>Mathematical equations</li> <ul> <li>Goldman-Hodgkin-Katz equation incorporates sodium, potassium, and chloride ions concentration gradients and membrane permeabilities</li> <li>Chord conductance equation uses conductance values and equilibrium potentials</li> </ul> <li>Sodium-potassium ATPase pump</li> <ul> <li>Active transport to exchange ions and maintain concentration gradients</li> <li>Exchanges three sodium ions out for two potassium ions in using ATP</li> </ul> </ul>
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FAQs
Resting membrane potential is the difference in voltage across the neuron cell membrane when the cell is at rest, typically around -65 to -70 mV (more negative inside). It is established by ion concentration gradients of sodium and potassium, selectively permeable leaky channels, electric gradients, and the active sodium-potassium ATPase pump. These factors contribute to maintaining a stable resting membrane potential that is crucial for a neuron's ability to transmit electrical signals.
Sodium and potassium ion concentration gradients play a significant role in establishing resting membrane potential. Inside the neuron, potassium concentration is high while sodium concentration is low, and the reverse is true outside the cell. The selective permeability of the neuron cell membrane, due to the presence of leaky channels, allows potassium ions to move more easily compared to sodium ions. This selective movement creates an electrical imbalance along the membrane, resulting in the resting membrane potential.
The Goldman-Hodgkin-Katz (GHK) equation calculates the membrane potential by considering the permeability and concentration gradients of various ions, such as sodium, potassium, and chloride. It is based on the chord conductance equation that calculates potential across multiple parallel conductances (ionic permeabilities). The GHK equation mathematically explains the contribution of each ion to the overall membrane potential, thereby allowing the prediction of the membrane's electrical behavior based on its ion permeabilities and concentrations.
The sodium-potassium ATPase pump is essential for maintaining the resting membrane potential as it actively transports ions against their concentration gradients. It exchanges 3 sodium ions from the inside of the cell for 2 potassium ions from the outside, using energy from ATP hydrolysis. This pump maintains the relative intracellular and extracellular ion concentrations, ensuring the neuron's ability to reach resting state after depolarization events such as action potentials or graded potentials.
Leaky channels, also known as passive ion channels, are crucial in maintaining the resting membrane potential in neurons. These channels are more permeable to potassium ions than sodium ions, allowing potassium ions to move more freely across the membrane. The continuous outflow of potassium ions due to these selective leaky channels creates a net negative charge inside the cell. Electric gradients and the forces that result from these charge differences work to maintain the stable resting membrane potential within the neuron.
