Resting membrane potential - definition, examples

Summary

This script delves into the science of cell membranes and resting membrane potential. It explains how concentration gradients and ion permeability across the membrane create this potential, focusing on the role of the sodium-potassium pump and the equilibrium potential for potassium, sodium, chloride, and calcium ions. The Nernst equation is introduced to calculate these potentials, revealing how the resting membrane potential is a balance of these individual ion potentials, primarily influenced by potassium due to its high permeability.

Takeaways

• 🔬 Each cell in the human body is surrounded by a membrane that separates the inner and outer environments.
• ⚡ Positively and negatively charged ions are not equally distributed across the membrane, creating differences in concentration and charge.
• 🚰 The sodium-potassium pump uses ATP to move three sodium ions out of the cell for every two potassium ions it moves in, establishing a concentration gradient.
• 📉 Potassium has a higher concentration inside the cell (150 mMol/L) compared to outside (5 mMol/L), creating a strong concentration gradient that pushes potassium out of the cell.
• 🔌 Potassium moves across the membrane through leak channels and inward rectifier channels, resulting in a negative charge buildup inside the cell.
• 📉 The equilibrium potential for potassium is about -92 mV, balancing the concentration gradient pushing potassium out and the electrostatic gradient pulling it back in.
• 🧮 The Nernst equation calculates the equilibrium potential for ions, taking into account their concentration inside and outside the cell.
• 📊 The resting membrane potential of a cell is influenced by the equilibrium potentials of potassium, sodium, chloride, and calcium, with potassium having the most significant effect.
• 🔄 Changing the permeability of the cell membrane to different ions can alter the cell's resting membrane potential.
• 💡 The cell's resting membrane potential is a summation of the equilibrium potentials of individual ions, weighted by their relative permeability.

Q & A

What is the primary function of the cell membrane?

The primary function of the cell membrane is to separate the inner environment of the cell from the outer environment, maintaining a difference in ion concentration and charge across its surface.

What establishes the cell's resting membrane potential?

The cell's resting membrane potential is established by differences in ion concentration and charge, as well as the permeability of the membrane to various ions.

What are the typical ion concentrations found inside and outside a cell?

Typically, there is a higher concentration of Na+, Cl-, and Ca2+ outside the cell, while K+ and negatively charged anions like amino acids and proteins are more concentrated inside the cell.

How does the sodium-potassium pump contribute to the resting membrane potential?

The sodium-potassium pump uses ATP to move three sodium ions out of the cell and two potassium ions into the cell, helping to establish the concentration gradient necessary for the resting membrane potential.

What is the role of potassium leak channels and inward rectifier channels in the cell membrane?

Potassium leak channels and inward rectifier channels allow potassium ions to move across the membrane, following the concentration gradient and contributing to the establishment of the resting membrane potential.

What is the equilibrium potential, and how is it related to the resting membrane potential?

The equilibrium potential, also known as the Nernst potential, is the point where the movement of an ion due to its concentration gradient equals the movement due to the electrostatic gradient. The resting membrane potential is influenced by the equilibrium potentials of the ions that are most permeable across the membrane.

What is the Nernst equation, and how is it used to calculate the equilibrium potential of an ion?

The Nernst equation is used to calculate the equilibrium potential (Vm) of an ion based on the ion's concentration outside and inside the cell. For a single-charged ion, Vm = 61.5 * log([ion]outside/[ion]inside), and for a double-charged ion, Vm = 30.75 * log([ion]outside/[ion]inside).

What are the equilibrium potentials for potassium, sodium, chloride, and calcium ions based on the given concentrations?

The equilibrium potentials are approximately -92 mV for potassium, +67 mV for sodium, -86 mV for chloride (since it's a negatively charged ion, the sign is flipped), and +123 mV for calcium.

How does the actual resting membrane potential of a cell differ from the individual ion equilibrium potentials?

The actual resting membrane potential is a summation of the individual ion equilibrium potentials, weighted by the relative permeability of each ion across the cell membrane at a given time.

How can a cell change its resting membrane potential?

A cell can change its resting membrane potential by altering its permeability to ions, for example, by adding or removing ion channels, which affects the proportion of each ion moving across the membrane.

What is the resting membrane potential of a cell if 90% of ions moving across the membrane are potassium ions, 1% are calcium ions, 1% are sodium ions, and 8% are chloride ions?

Given these proportions and their respective equilibrium potentials, the resting membrane potential would be approximately -86 mV, calculated as 90% of -90mV (-81 mV) + 1% of 123 mV (1.23 mV) + 1% of 67 mV (0.67 mV) + 8% of -86 mV (-6.88 mV).