Question

What is meant by depolarization? Repolarization? How, in general, are each of these accomplished? (Right now, you just need to know that positively-charged ions move and which direction they go in each case. We'll worry more about specifics of this when we talk about the nervous system.)

Answer 1

Depolarization is the phase of the action potential where Na+ ions enter a neuron, making it more positive inside, while repolarization follows when K+ ions leave the neuron, restoring its negative charge. Myelin sheaths on nerves provide insulation that accelerates nerve signal transmission.

Step-by-step explanation:

Depolarization and repolarization are two phases of the action potential in neurons. Depolarization occurs when sodium ions (Na+) flow into a neuron, making the inside of the neuron more positive and triggering the action potential. Repolarization occurs afterwards, as potassium ions (K+) move out of the neuron, restoring the negative charge inside the neuron and returning it to its resting state. Myelinated nerves have a covering of myelin, which acts as insulation, speeding up the transmission of action potentials through a process called saltatory conduction.

The movements of Na+ and K+ across the neuron's membrane are carefully regulated by voltage-gated channels. When a stimulus reaches a neuron, it causes these channels to open sequentially. The rapid influx of Na+ during depolarization causes the interior of the neuron to become more positive relative to the outside. Once the peak is reached, the Na+ channels inactivate and K+ channels open, allowing K+ to flow out and returning the neuron to its negative resting membrane potential, a phase known as repolarization.