Question

The resting membrane potential of a neuron or muscle cell is a. equal to the potassium equilibrium potential. b. equal to the sodium equilibrium potential. c. somewhat less negative than the potassium equilibrium potential. d. somewhat more positive than the sodium equilibrium potential. e. not changed by stimulation.

Short answer

The resting membrane potential of a neuron or muscle cell is somewhat less negative than the potassium equilibrium potential (option c). This is because it is influenced by the distribution of not only potassium ions but also other ions, such as sodium and chloride.

Step-by-step solution

Option a: Equal to the potassium equilibrium potential.

The resting membrane potential is slightly more negative than the potassium equilibrium potential due to the presence of other ions like sodium and chloride. Therefore, this option is incorrect.

Option b: Equal to the sodium equilibrium potential.

The resting membrane potential is less positive than the sodium equilibrium potential due to the higher ratio of potassium ions outside the cell compared to sodium ions inside the cell. Hence, this option is incorrect.

Option c: Somewhat less negative than the potassium equilibrium potential.

This option is correct. The resting membrane potential is slightly less negative than the potassium equilibrium potential because it is influenced not only by potassium ion distribution but also by other ions, such as sodium and chloride. These ions cause the resting membrane potential to be slightly higher than the potassium equilibrium potential.

Option d: Somewhat more positive than the sodium equilibrium potential.

The resting membrane potential is less positive than the sodium equilibrium potential, not more positive. Therefore, this option is incorrect.

Option e: Not changed by stimulation.

Upon stimulation, the resting membrane potential will undergo changes (such as depolarization) as the permeability of the cell membrane to different ions changes. So, this option is incorrect. In conclusion, the correct answer is option c: The resting membrane potential of a neuron or muscle cell is somewhat less negative than the potassium equilibrium potential.

Key concepts

Potassium Equilibrium Potential

The potassium equilibrium potential is a critical aspect of membrane potential in neurons. It refers to the electrical potential difference across the neuronal membrane that precisely balances the concentration gradient for potassium ions (K+).In simpler terms, it's the voltage at which there is no net flow of potassium ions in or out of the neuron. This is achieved when the outward chemical gradient of potassium ions, driving them out of the cell, is perfectly balanced by the inward electrical gradient attracting them back into the cell.
Mathematically, it can be determined using the Nernst equation:

• \[ E_{K} = \frac{RT}{zF} \ln \left( \frac{[K^+]_{outside}}{[K^+]_{inside}} \right) \]

where:

• \(E_{K}\) is the equilibrium potential for potassium,
• \(R\) is the gas constant,
• \(T\) is the absolute temperature,
• \(z\) is the charge of the ion, and
• \(F\) is Faraday's constant.

It's essential to understand that while the potassium equilibrium potential plays a significant role in the resting membrane potential, the membrane potential itself is not exactly equal to the potassium equilibrium potential because of the influence of other ions like sodium (Na+) and chloride (Cl-). This makes the resting membrane potential somewhat less negative than the potassium equilibrium potential.

Sodium Equilibrium Potential

The sodium equilibrium potential is similar to the potassium equilibrium potential but specifically refers to sodium ions (Na+) and the balance of forces acting on them.The sodium equilibrium potential is the voltage at which the inward chemical gradient of sodium ions is equal to the outward electrical gradient. This means there is no net movement of sodium ions across the neuronal membrane.
The Nernst equation is also used to calculate the sodium equilibrium potential:

• \[ E_{Na} = \frac{RT}{zF} \ln \left( \frac{[Na^+]_{outside}}{[Na^+]_{inside}} \right) \]

Differences between sodium and potassium ion concentrations inside and outside the cell lead to different equilibrium potentials for each ion. Typically, the sodium equilibrium potential is more positive than the resting membrane potential, reflecting the higher concentration of sodium ions outside the cell compared to inside.It's important to note that the sodium equilibrium potential contributes to the overall membrane potential of a neuron, particularly during events like action potentials when sodium permeability increases significantly.

Neuron Physiology

Neuron physiology revolves around the ability of neurons to transmit signals rapidly and precisely, which is central to all nervous system functions. A key aspect of neuron physiology is the membrane potential, a voltage difference across the cell membrane. This is primarily determined by the distribution of ions across the membrane, dictated by the equilibrium potentials of potassium and sodium, as well as chloride ions.

• **Resting Membrane Potential:** This is the baseline membrane potential of a neuron when it's not transmitting a signal. It's usually around -70 mV and is influenced primarily by the potassium equilibrium potential, as well as some contribution from sodium and chlorine equilibrium potentials.
• **Action Potentials:** These are rapid changes in the membrane potential that occur when neurons transmit signals. Action potentials are characterized by a fast depolarization (when Na+ channels open) followed by repolarization (when K+ channels open) of the membrane.
• **Ion Channels:** Specialized proteins in the neuron's membrane that regulate the flow of ions into and out of the cell, crucial for maintaining the resting membrane potential and generating action potentials.

Understanding these processes helps explain how neurons communicate and process information in the brain, underscoring the sophisticated nature of neuron physiology.