2-Minute Neuroscience: Action Potential

Summary

The video '2 Minute Neuroscience' succinctly explains the action potential, the electrical signal that underpins neuron communication. Starting from a resting potential of -70 mV, neurotransmitters cause depolarization, moving the neuron towards its threshold at -55 mV. Once reached, sodium channels open, leading to a rapid influx of sodium ions and a reversal of membrane potential, marking the action potential's rising phase. After peaking, potassium channels open, initiating repolarization and the falling phase, returning the neuron to its resting state, albeit briefly hyperpolarized during the refractory period. This process enables the transmission of signals along the neuron and the potential release of neurotransmitters to the next neuron.

Takeaways

• 🧠 The action potential is a fundamental mechanism for electrical signaling in neurons.
• ⚡ The resting membrane potential of a neuron is typically around -70 millivolts.
• 🔄 Depolarization occurs when neurotransmitters bind to receptors, making the membrane potential less negative and closer to 0.
• 📈 The neuron reaches a threshold membrane potential of approximately -55 mV, which triggers the action potential.
• 🚀 At the threshold, sodium channels open, allowing a rush of positively charged ions into the cell, creating the action potential.
• 📊 The action potential has a rising phase where the membrane potential becomes positive, followed by a peak.
• 🔄 The falling phase of the action potential involves the closing of sodium channels and the opening of potassium channels, leading to repolarization.
• 💥 The neuron may become hyperpolarized during the refractory period, making it difficult to trigger another action potential.
• 🔄 The refractory period is followed by the closing of potassium channels and a return to the resting membrane potential.
• 🔗 The action potential travels down the neuron and can lead to the release of neurotransmitters at the axon terminals, continuing the signal to the next neuron.

Q & A

What is the action potential in neuroscience?

The action potential is a brief reversal of the membrane potential that serves as the basis for electrical signaling within neurons.

What is the resting membrane potential of a neuron?

The resting membrane potential of a neuron is approximately -70 millivolts.

What is depolarization and how does it relate to the action potential?

Depolarization is the process where the neuron's membrane potential becomes less polarized, moving closer to 0, which is a precursor to the action potential.

What causes the neuron to reach its threshold membrane potential?

Repeated depolarization due to neurotransmitters binding to receptors on the dendrites can cause the neuron to reach its threshold membrane potential, typically around -55 mV for a neuron with a resting potential of -70 mV.

What happens when a neuron reaches its threshold membrane potential?

When the threshold is reached, many sodium channels open, allowing positively charged sodium ions to enter the cell, leading to a massive depolarization and the initiation of the action potential.

What is the rising phase of the action potential?

The rising phase of the action potential is when the influx of positive ions causes the membrane potential to go from 0 to a positive value, creating the electrical signal that travels down the neuron.

What occurs during the peak of the action potential?

At the peak of the action potential, sodium channels close and potassium channels open, allowing potassium ions to flow out of the cell, which initiates repolarization.

What is repolarization and what phase of the action potential does it occur in?

Repolarization is the process where the neuron's membrane potential returns to its resting state from a positive value, and it occurs during the falling phase of the action potential.

What is the refractory period and why is it significant?

The refractory period is a phase following repolarization where the neuron is hyperpolarized and less likely to fire again, making it a critical time for the neuron to reset and prepare for the next potential signal.

How does the action potential contribute to the transmission of signals in the nervous system?

The action potential travels down the neuron and can trigger the release of neurotransmitters at the axon terminals, allowing the signal to be passed on to the next neuron in the sequence.

What is the final step in the action potential process before the neuron is ready to be activated again?

The final step is when the potassium channels close and the membrane returns to its resting membrane potential, making the neuron ready to be activated again.

Outlines

00:00

🧠 Introduction to Action Potentials

This paragraph introduces the concept of action potentials in the context of neuroscience. It explains that action potentials are brief reversals of the membrane potential, which are fundamental to electrical signaling in neurons. The resting membrane potential is typically around -70 millivolts, and neurotransmitters can cause depolarization, making the potential less polarized and moving it closer to 0. The paragraph also introduces the concept of threshold membrane potential, which, when reached, triggers a large influx of sodium ions, leading to the rising phase of the action potential. The action potential then travels along the neuron, eventually reaching a peak before sodium channels close and potassium channels open, initiating repolarization and the falling phase of the action potential.

Keywords

💡Action Potential

Action potential refers to the rapid and temporary reversal of the electrical potential across the membrane of a neuron, which is fundamental to the process of neuronal communication. In the video, it is described as the basis for electrical signaling within neurons, where a momentary reversal of membrane potential occurs. The action potential is initiated when the neuron reaches a threshold membrane potential, leading to the opening of sodium channels and the influx of sodium ions, which is a critical step in the neuron's ability to transmit signals.

💡Membrane Potential

Membrane potential is the voltage difference across the cell membrane, which is essential for the neuron's function. In the context of the video, the resting membrane potential of a neuron is around -70 millivolts, indicating a state of relative electrical inactivity. The script explains how neurotransmitters can cause depolarization, reducing the membrane potential and moving it closer to zero, which is a precursor to the action potential.

💡Depolarization

Depolarization is the process by which the membrane potential of a neuron becomes less negative, moving towards zero. In the video, it is mentioned that when neurotransmitters bind to receptors on the dendrites, they can cause depolarization, which is a crucial step in the initiation of an action potential. The script illustrates this by stating that repeated depolarization can lead to the neuron reaching its threshold membrane potential.

💡Threshold Membrane Potential

Threshold membrane potential is the specific level of membrane potential at which an action potential is triggered. In the video, it is stated that for a neuron with a resting membrane potential of -70 mV, the threshold is generally around -55 mV. This concept is central to understanding how neurons decide to fire an action potential in response to stimuli.

💡Sodium Channels

Sodium channels are protein structures in the neuron's membrane that allow the passage of sodium ions. The video script explains that when the threshold membrane potential is reached, a large number of sodium channels open, allowing positively charged sodium ions to enter the cell, which is the driving force behind the rising phase of the action potential.

💡Repolarization

Repolarization is the process by which the neuron's membrane potential returns to its resting state after an action potential. In the video, it is described as the falling phase of the action potential, where potassium channels open and potassium ions flow out of the cell, helping to restore the membrane potential to its resting level.

💡Potassium Channels

Potassium channels are membrane proteins that facilitate the movement of potassium ions out of the cell. The script describes how, after the peak of the action potential, sodium channels close and potassium channels open, leading to the outflow of potassium ions and the process of repolarization.

💡Refractory Period

The refractory period is a brief interval following an action potential during which the neuron is less likely to generate another action potential. The video script mentions this phase, noting that after the neuron returns to its resting membrane potential, it overshoots and becomes hyperpolarized, making it difficult for the neuron to fire again during this period.

💡Neurotransmitter

Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another. The video script explains that the signal generated by the action potential can cause the release of neurotransmitters at the axon terminals, which is essential for passing the signal to the next neuron in the chain of communication.

💡Axon Terminals

Axon terminals, also known as synaptic terminals, are the end parts of an axon where neurotransmitters are released into the synaptic cleft. The video script refers to axon terminals as the location where neurotransmitters are released to pass the signal to the next neuron, illustrating the final step in the transmission of an action potential.

💡Synaptic Cleft

Although not explicitly mentioned in the script, the synaptic cleft is the space between the axon terminal of a neuron and the dendrite of another neuron, where neurotransmitters are released and bind to receptors. Understanding the synaptic cleft is important for grasping how action potentials lead to communication between neurons.

Highlights

The action potential is a momentary reversal of membrane potential that enables electrical signaling within neurons.

The resting membrane potential of a neuron is approximately -70 millivolts.

Depolarization occurs when neurotransmitters bind to receptors on dendrites, moving the membrane potential closer to 0.

Threshold membrane potential is reached at about -55 mV, triggering the action potential.

Sodium channels open at threshold, allowing positively charged sodium ions into the cell, causing massive depolarization.

The rising phase of the action potential is characterized by the influx of positive ions and the membrane potential becoming positive.

The action potential is an electrical signal that travels down the neuron.

At the peak of the action potential, sodium channels close and potassium channels open, initiating repolarization.

Repolarization, or the falling phase, involves potassium ions flowing out of the cell, returning the neuron to its resting state.

The neuron may become hyperpolarized before returning to the resting membrane potential.

The refractory period is a phase where it is difficult to trigger another action potential in the neuron.

The signal from the action potential can lead to neurotransmitter release at the axon terminals, passing the signal to the next neuron.

Understanding the action potential is fundamental to grasping how neurons communicate through electrical signals.

The process of depolarization and repolarization is crucial for the propagation of the action potential along the neuron.

The action potential's rising and falling phases are key components of the neuron's electrical signaling.

The refractory period plays a critical role in preventing continuous firing and maintaining the neuron's signaling integrity.

The entire action potential process is essential for the transmission of information between neurons.

Transcripts

Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics

in 2 minutes or less.

In this installment I will discuss the action potential.

The action potential is a momentary reversal of membrane potential that is the basis for

electrical signaling within neurons.

If you’re unfamiliar with membrane potential, you may want to watch my video on membrane

potential before watching this video.

The resting membrane potential of a neuron is around -70 millivolts.

When neurotransmitters bind to receptors on the dendrites of a neuron, they can have an

effect on the neuron known as depolarization.

This means that they make the membrane potential less polarized, or cause it to move closer

to 0.

This chart shows membrane potential on the y axis and time on the x axis.

When neurotransmitters interacting with receptors causes repeated depolarization of the neuron,

eventually the neuron reaches what is known as its threshold membrane potential.

In a neuron with a membrane potential of -70 mV, this is generally around -55 mV.

When threshold is reached, a large number of sodium channels open, allowing positively

charged sodium ions into the cell.

This causes massive depolarization of the neuron as the membrane potential reaches 0

and then becomes positive.

This is known as the rising phase of the action potential.

This influx of positive ions creates the electrical signal known as the action potential, which

then travels down the neuron.

Eventually the action potential reaches its peak, sodium channels close and potassium

channels open, which allows potassium to flow out of the cell.

This loss of positive potassium ions promotes repolarization which is known as the falling

phase of the action potential.

The neuron returns to resting membrane potential, but actually overshoots it and the cell becomes

hyperpolarized.

During this phase, known as the refractory period, it is very difficult to cause the

neuron to fire again.

Eventually the potassium channels close and the membrane returns to resting membrane potential,

ready to be activated again.

The signal generated by the action potential travels down the neuron and can cause the

release of neurotransmitter at the axon terminals to pass the signal to the next neuron.