Interactive Biology TV: Episode 12 - Absolute and Relative Refractory Periods

Presenter

• Leslie Samuel

Main Topics

• Absolute and Relative Refractory Periods
• Voltage Gated Sodium Channels

Introduction

• Discussion on absolute and relative refractory periods.
• Context: Action potential and voltage gated sodium channels.

Voltage Gated Sodium Channels

• States:
  • Closed
  • Open
  • Inactive
• Components:
  • Activation Gate
  • Inactivation Gate
• Mechanism:
  • Stimulus causes activation gate to open.
  • Inactivation gate closes automatically after 0.5 to 1 millisecond.

Action Potential Review

• A stimulus is needed to exceed the threshold for action potential.
• Voltage gated sodium channels open, allowing sodium ions to enter the cell, causing depolarization.

Absolute Refractory Period (ARP)

• Definition: Cannot initiate another action potential regardless of stimulus strength.
• Occurs when sodium channels are open or inactive.
• Key Point: Sodium channels must reset to closed state to be restimulated.

Relative Refractory Period

• Definition: Possible to initiate another action potential, but requires a stronger stimulus.
• Occurs when sodium channels start resetting to closed state.
• As channels reset, less stimulus is needed.

Conclusion

• Summary:
  • Absolute Refractory Period: No new action potential possible during open or inactive states of sodium channels.
  • Relative Refractory Period: New action potential possible with stronger stimulus as sodium channels reset.
• Next Steps: Further episodes to be watched for continued learning.