Problem 2 - Biology Concepts and Applications

Question

When a neuron is at rest ___________. a. it is at threshold potential b. gated sodium channels are open c. it holds less sodium than the interstitial fluid d. both a and \(c\)

Step-by-Step Solution

Answer

The correct answer is c. The neuron holds less sodium than the interstitial fluid when at rest.

Step 1: Understanding Resting Potential

A neuron at rest is in a state where it is not transmitting an active signal. This state is known as the resting potential. During this state, specific conditions related to ion concentrations and membrane potential exist.

Step 2: Identifying Resting Conditions

During resting potential, the neuron has more sodium ions outside the cell than inside. This means that the interior has less sodium compared to the surrounding interstitial fluid. This differential contributes to the resting membrane potential, which is usually around -70mV.

Step 3: Checking Sodium Channel Status

Gated sodium channels are typically closed when the neuron is at rest. They remain closed to maintain the resting potential until the neuron reaches a threshold that prompts them to open for depolarization.

Step 4: Analyzing Given Options

- Option (a): A neuron at threshold potential is not at rest; it is about to fire an action potential. - Option (b): Gated sodium channels are not open when the neuron is at rest. - Option (c): This condition is true as the neuron holds less sodium than the interstitial fluid when at rest. - Option (d): This is incorrect because option (a) is false.

Step 5: Conclusion

Based on the analysis, option (c) accurately describes a neuron at rest because it reflects the correct ion distribution without any misalignments like the other options.

Key Concepts

Neuron

A neuron is a fundamental unit of the brain and nervous system, responsible for conveying information throughout the body. When we talk about neurons, we often refer to their ability to transmit signals. But when a neuron is not actively sending a signal, it is in a state known as resting potential.
Resting potential is crucial as it sets the stage for transmitting impulses when needed. A neuron at rest isn't doing nothing; it is actively maintaining an environment where it can quickly respond to stimuli when necessary. It achieves this by controlling the flow of ions across its membrane. This resting state is essential for the neuron to be ready to spring into action whenever a new signal has to be transmitted.

Sodium Ions

Sodium ions play a vital role in establishing a neuron's resting potential. At rest, a neuron has a high concentration of sodium ions outside the cell. This concentration gradient is maintained by sodium-potassium pumps which actively transport sodium ions out of the neuron while bringing potassium ions in.
This pump creates a difference in ion concentration across the neuron's membrane.

• Sodium ions are more abundant outside the neuron.
• Potassium ions are more abundant inside the neuron.

This differential ensures that when the neuron is at rest, it maintains a stable internal environment compared to its surroundings. The controlled movement of these ions is what allows the neuron to maintain its resting potential and be prepared for activation.

Membrane Potential

Membrane potential refers to the voltage difference across a cell's membrane. For neurons at rest, this is known as the resting membrane potential, typically measured at around -70mV. This voltage difference is crucial as it equips the neuron to rapidly generate an action potential when stimulated.
The resting membrane potential is primarily established by sodium and potassium ions. But why is this potential negative? It arises due to the movement and distribution of these ions.

• More potassium ions flow out of the neuron than sodium ions flow in, leading to a net negative charge inside.
• Sodium-potassium pumps work continuously to maintain this balance, pumping sodium ions out and potassium ions in.

Together, these ion movements through the neuron membrane help maintain a stable resting state, enabling the neuron to function efficiently and reliably.