Resting and Action Potential Lecture

Jul 13, 2024

Resting and Action Potential Lecture by Dr. Jimmy

Introduction

  • Dr. Jimmy explains resting and action potential for AS and A-Level Biology students.
  • The concept can be challenging, so he uses a slide deck animation to aid understanding.

Resting Potential

  • Axon Membrane: Plays a role in the generation of an action potential.
    • Contains sodium-potassium pumps.
    • For every 3 sodium ions pumped out, 2 potassium ions are pumped in.
    • Result: Inside of the axon becomes more negative.
  • Sodium and Potassium Channels: Open all the time.
    • More potassium channels than sodium channels.
    • Potassium diffuses out more than sodium diffuses in, maintaining negativity inside the axon.
  • Resting Potential Value: -60 to -70 millivolts.

Generation of an Action Potential

  • Voltage-Gated Channels: Sodium-gated and potassium-gated channels are triggered by electrical impulses.
  • When a stimulus reaches the axon:
    • Sodium-gated channels open, sodium ions flow inside.
    • Membrane potential increases from -70 mV to -50 mV (threshold potential).
    • More sodium channels open, increasing potential to +30 mV (depolarization phase).
  • Depolarization: Sodium influx makes the inside of the axon more positive up to +30 millivolts.
  • After ~1 millisecond, sodium channels close, potassium channels open. Potassium flows out, making inside negative again (repolarization phase).
  • Repolarization: Inside returns to more negative values, eventually to resting potential (-70 mV).
  • Hyperpolarization: Potassium channels close slowly, making inside briefly more negative than resting potential.

Cycle of Resting and Action Potential

  • Potassium ions outside, sodium ions inside enable the sodium-potassium pump to work again.
  • Sodium pumped out, potassium pumped in, restoring resting potential.

Practical Application

  • Students should try to fit this sequence onto a graph for exams.
  • Key Graph Points:
    • Resting Potential (-70 mV), threshold potential (-50 mV), depolarization (+30 mV), repolarization (back to -70 mV), hyperpolarization.
  • Key Structures:
    • Sodium-potassium pump, sodium channels, potassium channels, gated channels.

Conclusion

  • Understanding this cycle is crucial for explaining the resting and action potential graph in exams.
  • Next video will cover synapses.