Exam 3 High Yield Review: Membrane and Action Potential

Membrane and Action Potential (Lectures 16)

Transport Review

• Review Exam 2 high yield material, specifically Lecture 5 up to 6 minutes and 28 seconds.
• Focus on the difference between active and passive transport.
• Pay attention to facilitated diffusion, especially channel proteins.
• Understand the sodium-potassium pump as primary active transport using ATP directly.

Components of Nervous Tissue

• Neurons: Conduct action potentials, which involve the movement of ions across the membrane.
• Glial cells: Support cells with various functions (glia means "glue").

Potentials

• Potentials refer to voltage differences across membranes.

Membrane Potential

• Definition: Voltage difference across the membrane.
• One side is positive, and the other is negative due to ion concentration (primarily) and some proteins.
• Measured in millivolts (mV).

Resting Potential

• Definition: Membrane potential of the membrane at rest.
• Negative on the inside and positive on the outside.
• Varies from cell to cell:
  • Epithelial cell: approximately -50 mV.
  • Neuron: approximately -70 mV (depends on the type of neuron).
  • Muscle cell: approximately -90 mV (depends on the type).

Action Potential

• Definition: Changes in voltage from the resting potential.
• The voltage flips: positive on the inside and negative on the outside.
• Due to ions moving across the membrane via channel proteins.

Resting Potential and Ion Channels/Pumps

• Key point: Inside is negative, and outside is positive.

Sodium-Potassium Pump (Na+/K+ ATPase)

• Uses primary active transport (ATP directly).
• Pumps 3 sodium ions (Na^+) outside the cell and 2 potassium ions (K^+) inside the cell.

Ion Channels (Leak Channels)

• Sodium leak channels and potassium leak channels.
• Utilize facilitated diffusion.
• Move ions along their concentration gradient.

Combined Action of Sodium-Potassium Pump and Leak Channels

• Sodium-potassium pump removes more positive charges (3 \Na^+ out) than it brings in (2 \K^+ in).
• Sodium leak channels allow positively charged sodium ions to leak out.
• Potassium leak channels allow even more positively charged potassium ions to leak out.
• Result: More positive charges on the outside, making the inside more negative.

Potassium Leak Channels as Main Driver

• Potassium leak channels are the main driver of the resting potential because they are responsible for more positive charges leaving the inside.

Review and Summary

• Understand membrane potential, resting potential, and action potential.
• Resting potential: negative inside, positive outside.
• Action potential: flips to positive inside, negative outside.
• Different ion channels set up these potentials.
• Lecture 16 ends content for Exam 3 (up to slide 29, not including).