Membrane Potential, Equilibrium Potential and Resting Potential, Animation

Summary

The video explains the concept of membrane potential, which refers to the electric charge difference across a cell membrane. It covers how ions move based on concentration gradients and electrostatic forces, and how membrane permeability to specific ions influences this movement. The equilibrium potential for ions like sodium, potassium, and chloride is discussed, illustrating how different ion gradients contribute to the resting membrane potential. The role of the sodium-potassium pump in maintaining this potential is highlighted, emphasizing its importance in generating action potentials. This process is crucial for the cell’s physiological functions and responses to stimulation.

Takeaways

• 😀 Membrane potential refers to the difference of electric charges across a cell membrane, typically with a negative charge inside the cell.
• 😀 The two main rules governing ion movement are: ions move from high to low concentration, and ions move toward opposite charges and away from like charges.
• 😀 Ion channels regulate the permeability of the membrane to specific ions, and this permeability can change with the cell's physiological state.
• 😀 If a membrane is equally permeable to both sodium and chloride ions, they will diffuse until both sides have the same concentration, resulting in zero membrane potential.
• 😀 When a membrane is permeable only to sodium ions, they diffuse down their concentration gradient, causing one side of the membrane to become positive and the other negative.
• 😀 At equilibrium, the diffusion force and electrostatic force on sodium ions balance out, resulting in no net movement of sodium and an established voltage known as the equilibrium potential for sodium.
• 😀 The equilibrium potential can be calculated based on the concentration gradient of ions and represents the voltage needed to balance ion movement.
• 😀 Neurons have unequal ion distributions across their membranes, which create gradients that contribute to the equilibrium potentials of different ions.
• 😀 Sodium has a positive equilibrium potential, potassium has a negative equilibrium potential, and chloride has an equilibrium potential that is close to the resting membrane potential.
• 😀 The resting membrane potential of a neuron is approximately -70mV, and chloride ions are in equilibrium at this potential, while sodium and potassium are not.
• 😀 The sodium-potassium pump actively transports sodium out of the cell and potassium into the cell to maintain unequal ion concentrations, which is essential for generating action potentials in neurons.

Q & A

What is membrane potential?

Membrane potential refers to the difference in electric charges across a cell membrane. It is typically negative in most cells, meaning there are more negative charges inside the cell than outside.

How is the movement of ions governed?

Ions move from areas of higher concentration to areas of lower concentration, and as charge-bearing particles, they also move away from like charges and toward opposite charges.

What role does membrane permeability play in ion movement?

The permeability of the membrane to specific ions controls ion movement. Ion channels open and close to allow or block the flow of ions, and this permeability can change depending on the cell's physiological state.

What happens when two solutions of different sodium chloride concentrations are separated by a membrane?

If the membrane is equally permeable to both sodium and chloride ions, both ions will diffuse from higher to lower concentrations, eventually equalizing the concentrations in both solutions, and the membrane potential will be zero.

What occurs when the membrane is only permeable to sodium ions?

If the membrane is only permeable to sodium ions, they will diffuse down their concentration gradient, causing one side to become increasingly positive and the other increasingly negative. This creates two opposing forces: diffusion and electrostatic forces.

What is the equilibrium potential for sodium?

The equilibrium potential for sodium is the voltage that balances both the diffusion force and the electrostatic force, resulting in no net movement of sodium across the membrane.

How does the equilibrium potential for different ions vary?

The equilibrium potential for different ions varies based on their concentration gradients. For example, the equilibrium potential for sodium is positive because its concentration gradient drives it into the cell, while potassium’s equilibrium potential is negative due to its reverse concentration gradient.

Why does chloride have a negative equilibrium potential?

Chloride has a negative equilibrium potential because, although its concentration gradient drives it into the cell, it is a negatively charged ion, and therefore needs a negative internal environment to move out of the cell.

What is the resting membrane potential of a neuron?

The resting membrane potential of a neuron is approximately -70 mV. This is mainly due to the unequal distribution of ions across the cell membrane, particularly sodium, potassium, and chloride.

Why are sodium and potassium not at equilibrium in resting neurons?

Sodium and potassium are not at equilibrium in resting neurons because the sodium-potassium pump actively transports sodium out of the cell and potassium into the cell, maintaining the concentration gradients necessary for action potential generation.