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2-Minute Neuroscience: Action Potential
Neuroscientifically Challenged
Overview
This video explains the action potential, the fundamental electrical signal in neurons. It details the process starting from the resting membrane potential, how depolarization reaches the threshold, the rapid influx of sodium ions causing the rising phase, the subsequent outflow of potassium ions during the falling phase (repolarization and hyperpolarization), and the refractory period that prevents immediate re-firing. This electrical signal is crucial for transmitting information throughout the nervous system.
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Chapters
- The action potential is a brief reversal of the neuron's membrane potential.
- It serves as the basis for electrical signaling within neurons.
- Understanding resting membrane potential is prerequisite knowledge.
This chapter introduces the core concept of neuronal electrical signaling, setting the stage for understanding how neurons communicate.
- Neurotransmitters binding to dendrites cause depolarization, making the membrane potential less negative (closer to 0).
- Repeated depolarization can lead the neuron to reach its threshold potential (around -55 mV).
- The resting membrane potential is typically around -70 mV.
This explains the initial trigger and the critical 'all-or-none' point that must be reached for a neuron to fire an electrical signal.
When neurotransmitters bind to receptors, they cause the inside of the neuron to become less negative, moving the membrane potential from -70 mV towards -55 mV.
- Upon reaching threshold, voltage-gated sodium channels rapidly open.
- Positively charged sodium ions rush into the cell, causing massive depolarization.
- This rapid influx creates the rising electrical signal of the action potential, making the membrane potential positive.
This phase represents the rapid generation of the electrical impulse itself, driven by the movement of ions across the neuronal membrane.
The sudden opening of sodium channels allows a flood of positive charges into the neuron, causing the electrical charge inside the cell to quickly become positive.
- At the peak of the action potential, sodium channels close and potassium channels open.
- Potassium ions flow out of the cell, reducing the positive charge inside.
- This outflow causes repolarization, returning the membrane potential towards resting levels, often overshooting to become hyperpolarized (more negative than resting potential).
This phase is crucial for resetting the neuron's electrical state and introduces a temporary period where firing is difficult, preventing continuous signaling.
As potassium leaves the cell, the internal electrical charge decreases, bringing the membrane potential back down and even making it more negative than the initial resting state.
- The hyperpolarized state creates a refractory period, making it difficult for the neuron to fire again immediately.
- Eventually, ion channels close, and the membrane returns to its resting potential.
- The generated action potential travels down the axon to the axon terminals, enabling signal transmission to the next neuron.
This explains how the neuron recovers and prepares for subsequent signals, and how the action potential ultimately communicates information to other cells.
After firing, the neuron becomes temporarily unresponsive, ensuring that the electrical signal is discrete and moves in one direction down the neuron.
Key takeaways
- The action potential is an 'all-or-none' electrical signal generated when a neuron's membrane potential reaches a specific threshold.
- Ion movement (sodium in, potassium out) across the neuronal membrane is the physical basis of the action potential.
- Depolarization brings the membrane potential closer to the threshold, while repolarization and hyperpolarization restore and temporarily lower the potential.
- The refractory period ensures unidirectional signal propagation and prevents immediate re-firing.
- Action potentials are the fundamental mechanism by which neurons transmit information throughout the nervous system.
Key terms
Action PotentialMembrane PotentialResting Membrane PotentialDepolarizationThreshold PotentialSodium ChannelsPotassium ChannelsRepolarizationHyperpolarizationRefractory Period
Test your understanding
- What is the primary function of an action potential in a neuron?
- How does depolarization contribute to reaching the threshold potential for an action potential?
- What role do sodium and potassium ions play during the rising and falling phases of an action potential?
- Why is the refractory period important for neuronal communication?
- What happens to the membrane potential during hyperpolarization, and why does it occur?