Lecture on Action Potentials

Introduction

• Previous lectures discussed how cells utilize voltage and concentration differences across membranes for work.
• Voltage changes and concentration differences also signal cells for other tasks.

Action Potential

• Definition: A rapid change in membrane potential involving ion concentration and voltage.
• It signifies a shift from the resting membrane potential, which is the cell's homeostasis or set point.

Importance of Resting Membrane Potential

• Resting potential is typically around -70 millivolts.
• Maintaining this potential is crucial for cell function.

Mechanism of Action Potential

• Involves changes in membrane permeability to specific ions, particularly sodium (Na+) and potassium (K+).
• Conductance: Ability of ions to traverse the membrane impacts action potential.

Detailed Process of Action Potential

Depolarization Phase

• When membrane potential shifts to around -55 mV, sodium channels open.
• Sodium influx due to high external concentration and internal negativity.
• Result: Rapid increase in internal cell positivity.

Repolarization Phase

• Sodium channels close at peak positivity.
• Potassium channels open, allowing K+ to exit.
• Result: Rapid decrease in internal positivity.

Hyperpolarization Phase

• Membrane potential becomes more negative than resting potential.
• Sodium-potassium pump restores resting potential by expelling Na+ and importing K+.

Graphical Representation

• Graphs show changes in membrane potential and ion conductance over time.
• Sodium conductance spikes during depolarization, while potassium spikes during repolarization.

Visual Explanation

• Cell membrane depicted with closed sodium and potassium ion channels.
• Sodium concentration higher outside, potassium higher inside.
• Negative proteins contribute to internal negativity.

Resting State Factors

• Sodium-potassium pump maintains ionic balance.
• Membrane permeable to potassium due to open channels.

Summary of Phases

• Depolarization: Sodium entry, potential becomes positive.
• Repolarization: Potassium exit, potential becomes negative.
• Hyperpolarization: More negative than resting potential, sodium-potassium pump reestablishes set point.

Conclusion

• Action potential is crucial for cellular signaling and function.
• Understanding facilitated by lab activities.