Describe the steps of the action potential (as it travels down the axon of a neuron).
The correct answer and explanation is:
Correct Answer:
The steps of an action potential traveling down the axon of a neuron include:
- Resting Potential
- Depolarization
- Repolarization
- Hyperpolarization
- Return to Resting Potential
300-Word Explanation:
An action potential is an electrical signal that travels down the axon of a neuron to transmit information. It is a rapid, temporary change in the membrane potential that allows communication between neurons or between neurons and muscles.
- Resting Potential:
At rest, the inside of a neuron is negatively charged relative to the outside (about -70 mV). This is maintained by the sodium-potassium pump, which moves 3 Na⁺ ions out and 2 K⁺ ions into the cell, and by leak channels that allow more K⁺ to leave than Na⁺ to enter. - Depolarization:
When a neuron is stimulated past a certain threshold (around -55 mV), voltage-gated sodium (Na⁺) channels open, allowing Na⁺ to rush into the cell. This influx causes the inside of the cell to become more positive, reaching up to +30 mV. - Repolarization:
Soon after depolarization, Na⁺ channels close and voltage-gated potassium (K⁺) channels open. K⁺ ions flow out of the cell, restoring the negative internal charge. - Hyperpolarization:
K⁺ channels stay open slightly longer than needed, causing the membrane potential to become more negative than the resting potential (around -80 mV). This prevents the neuron from firing again too quickly (refractory period). - Return to Resting Potential:
Finally, all ion channels reset. The sodium-potassium pump restores the original distribution of ions, returning the neuron to its resting potential, ready for the next action potential.
The action potential travels along the axon like a wave, with each segment undergoing these changes in sequence. This rapid signaling is essential for nervous system function, including muscle movement, sensation, and thought.