Question

An action potential involves Na+ moving ________ the cell and K+ moving ________ the cell. a. inside; outside b. outside; inside c. inside; inside d. outside; outside

Short answer

The correct answer is a. Na+ moves inside the cell and K+ moves outside the cell during an action potential.

Step-by-step solution

Understand an Action Potential

During an action potential, a neuron receives a signal and this causes cell membrane channels to open and allow sodium ions (Na+) to flow into the cell. This results in the cell's interior becoming more positive, producing the initial part of the action potential.

K+ ion Movement

After the influx of Na+ ions, potassium ions (K+) start to leave the cell. This movement of K+ ions out of the cell brings the membrane potential back to a negative value, ending the action potential.

Match the Mechanism to the Choices

Since Sodium ions (Na+) move into the neuron and Potassium ions (K+) move out of the neuron during an action potential, the correct answer is the choice that states: 'Na+ moves inside the cell and K+ moves outside the cell'.

Key concepts

Neuron Signal Transmission

Imagine the nervous system as a complex network of highways, with messages speeding along from one destination to another. This is essentially the role of neurons in neuron signal transmission. Each neuron is like a city, sending and receiving signals to and from other cities, or in this case, other cells within the body.

An action potential is the special 'vehicle' that travels on these highways, carrying important information. It's created when a neuron sends a signal down its axon to communicate with another neuron or muscle cell. The process begins when certain triggers cause a sudden change in the electrical state of the neuron's membrane, leading to a domino effect that races along the neuron's length.

In simple terms, the neuron 'fires' by rapidly changing the electrical charge from negative to positive and back to negative again, allowing the message to leap from one node to the next, much like the quick successions of a zip line between towers.

Sodium-Potassium Pump

To maintain this precise communication, neurons rely on a molecular device known as the sodium-potassium pump. This pump is an essential protein found in the cell membrane that acts like a dedicated gatekeeper, controlling the movement of ions into and out of the neuron.

The pump uses energy in the form of ATP to move three sodium ions (Na+) out of the cell and two potassium ions (K+) into the cell, against their concentration gradients. This activity is key because it helps to restore and maintain the neuron's resting membrane potential after an action potential has occurred, essentially 'recharging' the neuron's battery so it's ready to fire again. It's a meticulous balance of ions that the pump must maintain, and it's vital for healthy neural functions such as muscle contractions, heartbeat rhythm, and even your ability to read this text.

Membrane Potential

The term 'membrane potential' refers to the electrical voltage difference across the cell membrane. Due to the action of the sodium-potassium pump and other ion channels, there's a higher concentration of positive sodium ions outside the neuron, and a higher concentration of negative charge inside.

Think of this as a charged-up battery: the inside of the neuron is like the negative end, and the outside is like the positive end. This charge difference is the neuron's resting state, calmly waiting for a signal to activate it. During an action potential, this delicate balance temporarily topples, allowing sodium ions to rush into the cell, reversing the charge, and then potassium ions spill out to reset the original polarity.

This flip-flop of charges is vital for generating an action potential, and thus for signaling in the nervous system. Without membrane potential, our neurons would be unable to communicate, and our nervous system would be out of commission.