Question

1. which stage of action potential comes when an impulse arrives at the axon?

1. what does the impulse cause during depolarization?

1. when the na+ channels open during depolarization, what happens to sodium?

1. what does this rush in of na+ cause?

1. once na+ rushes in and is at equilibrium (ex. 4 inside, 4 outside) is there a concentration gradient of na+ anymore?

1. if there is no concentration gradient, what happens to the sodium voltage - gated channels?

1. after depolarization, which stage of action potential comes next?

1. what happens at the beginning of repolarization?

1. when the k+ channels open, what happens to potassium?

1. what does this rush out of k+ cause?

Explanation:

These questions are about the action potential in neurons, which is a topic in Biology (a subfield of Natural Science). Let's answer each:

1. When an impulse arrives at the axon, the first stage of action potential is Depolarization. The arrival of the impulse triggers the opening of voltage - gated sodium channels.

1. During depolarization, the impulse causes voltage - gated sodium channels to open. This is the initial event that starts the change in membrane potential.

1. When Na⁺ channels open during depolarization, sodium (Na⁺) rushes into the neuron (from the extracellular fluid to the intracellular fluid). This is because there is a higher concentration of Na⁺ outside the neuron and the channels are now open, allowing diffusion down the concentration gradient.

1. The rush in of Na⁺ causes the membrane potential to become more positive (depolarization). The influx of positive Na⁺ ions makes the inside of the neuron less negative (or even positive) compared to the resting state.

1. If Na⁺ is at equilibrium (equal concentration inside and outside, like 4 inside and 4 outside), there is no concentration gradient for Na⁺ anymore. A concentration gradient exists when there is a difference in concentration between two areas; if they are equal, the gradient is zero.

1. If there is no concentration gradient, the sodium voltage - gated channels close (inactivate). Once the concentration gradient is gone, these channels stop allowing Na⁺ to pass, and they enter an inactivated state during the action potential process.

1. After depolarization, the next stage of action potential is Repolarization. After the sodium channels inactivate, potassium channels start to open, leading to repolarization.

1. At the beginning of repolarization, voltage - gated potassium channels open. This allows potassium (K⁺) to move out of the neuron, starting the process of restoring the negative membrane potential.

1. When K⁺ channels open, potassium (K⁺) rushes out of the neuron (from the intracellular fluid to the extracellular fluid). There is a higher concentration of K⁺ inside the neuron at rest, so when the channels open, K⁺ diffuses down its concentration gradient.

1. The rush out of K⁺ causes the membrane potential to become more negative (repolarization, and eventually hyperpolarization in some cases). The loss of positive K⁺ ions from the inside of the neuron makes the membrane potential more negative, moving back towards (or beyond) the resting membrane potential.

Answer:

1. Depolarization
2. Voltage - gated sodium channels to open
3. Sodium rushes into the neuron
4. The membrane potential to become more positive (depolarization)
5. No
6. The sodium voltage - gated channels close (inactivate)
7. Repolarization
8. Voltage - gated potassium channels open
9. Potassium rushes out of the neuron
10. The membrane potential to become more negative (repolarization/hyperpolarization)