Action Potential Animation

Summary

This video explains the process of action potential generation in neurons. It details how a threshold stimulus causes voltage-gated sodium channels to open, leading to depolarization as sodium ions enter the axon. The potential then repolarizes as potassium channels open, allowing potassium ions to exit. A brief hyperpolarization phase occurs before the membrane returns to its resting potential. This cycle enables the neuron to transmit signals across long distances, preparing it for the next action potential.

Takeaways

• 😀 Neurons send signals over long distances by generating and propagating action potentials.
• 😀 Action potentials originate near the axon hillock of the cell body in the initial segment of the axon.
• 😀 Voltage-gated channels open and close, altering the membrane's permeability to sodium and potassium ions during an action potential.
• 😀 A threshold stimulus activates voltage-gated sodium channels, starting the depolarization phase of the action potential.
• 😀 During depolarization, sodium ions diffuse into the axon, making the membrane potential less negative and eventually reaching +30 mV.
• 😀 At +30 mV, sodium channel inactivation gates close and potassium channels open, initiating the repolarization phase.
• 😀 In repolarization, potassium ions diffuse out of the axon, restoring the membrane potential to a negative value.
• 😀 Hyperpolarization occurs when the membrane potential becomes more negative than the resting state, beyond -70 mV.
• 😀 During hyperpolarization, potassium channels close and sodium channels are released from inactivation.
• 😀 The membrane potential returns to the resting state of -70 mV, and the neuron is ready to fire another action potential.

Q & A

What initiates the generation of an action potential in a neuron?

A threshold stimulus initiates the generation of an action potential by triggering the opening of voltage-gated sodium channels.

Where do most action potentials originate in the neuron?

Most action potentials originate near the axon hillock, specifically in the initial segment of the axon.

What happens during the depolarization phase of an action potential?

During depolarization, voltage-gated sodium channels open, allowing sodium ions to diffuse into the axon, making the membrane potential less negative and eventually reaching +30 mV.

What triggers the opening of more voltage-gated sodium channels during depolarization?

The initial depolarization of the membrane triggers the opening of additional voltage-gated sodium channels, causing further depolarization and a positive feedback loop.

What occurs at +30 mV during the action potential?

At +30 mV, the inactivation gates of voltage-gated sodium channels close, and voltage-gated potassium channels open, marking the transition to the repolarization phase.

What is the primary ion movement during the repolarization phase?

During repolarization, potassium ions diffuse out of the axon, causing the membrane potential to become negative again.

What is hyperpolarization, and how does it occur?

Hyperpolarization occurs when the membrane potential becomes more negative than the resting state, caused by the continued efflux of potassium ions after the repolarization phase.

How does the neuron return to its resting membrane potential after hyperpolarization?

After hyperpolarization, voltage-gated potassium channels close, and the membrane potential returns to the resting state of -70 mV, mainly through leak channels.

Why are the inactivation gates of sodium channels important during an action potential?

The inactivation gates of sodium channels close at +30 mV to stop the influx of sodium ions, ensuring that the action potential does not reverse and progress properly toward repolarization.

What is the role of leak channels in maintaining the resting potential?

Leak channels allow ions to flow in and out of the neuron, helping to maintain the resting membrane potential of -70 mV once the action potential has completed.