Question

After an action potential, the opening of additional voltage-gated _____ channels and the inactivation of sodium channels, cause the membrane to return to its resting membrane potential. a. sodium b. potassium c. calcium d. chloride

Short answer

Answer: (b) Potassium

Step-by-step solution

Understand the action potential sequence

Action potentials involve the opening and closing of voltage-gated ion channels in the membrane of a neuron. Initially, sodium channels open and allow positively charged sodium ions to flow into the cell, causing depolarization, i.e., the inside of the cell becoming more positive. This is the rising phase of the action potential. Subsequently, these sodium channels start to inactivate, and additional voltage-gated channels open that allow other ions to flow across the membrane and lead to the return to the resting membrane potential.

Analyze the given answer choices

We are provided with four options; sodium, potassium, calcium, and chloride ion channels. As mentioned in step 1, sodium channels become inactivated after the peak of an action potential, so they do not help in the return to the resting membrane potential. Therefore, option (a) can be ruled out.

Determine the correct answer

After an action potential, the opening of voltage-gated potassium channels is what allows positively charged potassium ions to flow out of the cell, causing the inside to become more negative, ultimately returning the membrane potential to its resting state. Hence, the correct answer to this question is option (b) potassium.

Key concepts

Voltage-gated Ion Channels

Voltage-gated ion channels are crucial in the generation and propagation of action potentials in neurons. These channels are highly sensitive to changes in membrane potential.
When a certain voltage threshold is reached, they open, allowing ions to flow across the neuron's membrane.

• The opening of these channels typically initiates the depolarization phase of the action potential by allowing ions like sodium to flow into the neuron.
• As the potential changes further, different ion channels, such as potassium, become activated to help restore the resting state.

The precise timing of the opening and closing of these channels ensures the action potential propagates efficiently along the neuron.

Depolarization

Depolarization is a critical phase in the action potential sequence. During depolarization, the membrane potential becomes less negative.
This phase is initiated by the opening of voltage-gated sodium channels, allowing an influx of sodium ions into the neuron.

• The rapid influx of sodium ions changes the neuron's internal charge from negative to positive.
• This charge shift allows the action potential to reach its peak.

Depolarization is essential for transmitting nerve signals and ensures communication between neurons.

Resting Membrane Potential

The resting membrane potential is the stable, negative charge of a neuron's membrane when it's not actively sending a signal.
This potential is typically around -70 mV.
It is maintained by several factors:

• Sodium-potassium pumps actively transport sodium out of and potassium into the cell, creating an electrochemical gradient.
• Potassium leak channels allow a slow exit of potassium ions, helping maintain the negative resting potential.

The resting membrane potential serves as the baseline from which neurons can fire action potentials.

Neuron Function

Neurons are the basic building blocks of the nervous system. They transmit information throughout the body using electrical impulses called action potentials.
Neuron function is key to everything from muscle contraction to processing thoughts.

• When a neuron receives a signal, it initiates an action potential.
• This involves a precisely choreographed opening and closing of voltage-gated ion channels.

The action potential travels down the length of the neuron to communicate with other cells, allowing the nervous system to send rapid messages.

Potassium Channels

Potassium channels play a pivotal role during the repolarization phase of an action potential.
After the peak of depolarization, these channels open to allow potassium ions to exit the cell.

• The efflux of positively charged potassium ions helps restore the negative interior of the neuron.
• This repolarization is essential for the neuron to return to its resting membrane potential.

Efficient functioning of potassium channels is vital to ensure neurons are ready for subsequent action potentials.