Lecture Notes: Understanding Action Potentials

Introduction to Action Potentials

• Action potentials, nerve impulses, or electrical impulses are terms used interchangeably to describe signals traveling along neurons.
• These signals travel from sensory neurons to relay neurons to motor neurons, depicted as arrows.

Misconceptions about Action Potentials

• Common misconception: Action potentials are not electrons moving along neurons (unlike electricity in physics).

Textbook Definition

• Action Potential Definition: Rapid change in electrical charge distribution across a cell surface membrane.
• This definition can be confusing initially; a deeper breakdown is needed.

Breakdown of Key Concepts

Cell Surface Membrane

• Location: Found along the axon of neurons.
• Structure: Includes a phospholipid bilayer and is simplified in diagrams as lines.

Electrical Charge Distribution

• Inside the Axon: More negative charge.
• Outside the Axon: More positive charge.
• Caused by Ions: Positively charged ions like sodium and potassium influence this distribution.

Membrane Potentials

• Represented by positive (outside) and negative (inside) symbols.
• Implies higher voltage outside and lower inside.
• This concept will be expanded in further studies on resting membrane potential.

Action Potential Process

Initial State

• Axon without Signal: No action potentials yet, but electrical charge distribution is necessary.
• Requirement: Outside must be more positive, inside more negative before any signal can be sent.

Rapid Change Mechanism

• When stimulated, the charge at a point (A) flips—inside becomes positive, outside negative.
• This rapid change moves sequentially along the axon to point (B), reverting to normal after passing.

What Happens During Action Potential

• Sequence: Charge changes rapidly from A to B, each section returning to its initial state post-change.
• Not Electron Movement: It is about changes in charge distribution, not physical movement of electrons.

Conclusion & Next Steps

• Understanding the axon’s charge distribution is crucial before studying resting membrane potential.
• Future topics will cover the specific causes of these charge changes and their propagation along the axon.