Transmembrane potentials

Introduction

A transmembrane potential describes the electrical voltage between the inside and outside of a cell membrane. It is created by the uneven distribution of ions and is essential for many biological processes.

Development of the transmembrane potential

1. Ion distribution

Inner space: High concentration of potassium ions (K⁺), many negatively charged proteins.
Outer space: High concentration of sodium ions (Na⁺) and chloride ions (Cl-).

2. Membrane permeability

The cell membrane is semi-permeable and contains special ion channels. Potassium flows preferentially out of the cell, making the inside of the cell more negative.

3. Sodium-potassium pump

An active transport mechanism that pumps 3 Na⁺ ions out and 2 K⁺ ions into the cell. This helps to maintain the negative potential.

Typical values

Resting membrane potential: about -70 mV (in nerve cells).
Depolarisation: cell interior becomes less negative.
Hyperpolarisation: Cell interior becomes more negative.

Significance and function

Nerve conduction: Basis for action potentials.
Muscle contraction: Control of muscle activity.
Cardiac function: Control of the heart rhythm.
Sensory functions: Conversion of stimuli into electrical signals.

Important concepts

Goldman-Hodgkin-Katz equation: Calculation of the membrane potential.
Action potential: Rapid change in membrane potential.
Electrochemical gradient: Combination of chemical and electrical gradient.

Summary

The transmembrane potential is essential for electrical excitability and communication in biological systems. It forms the basis for nerve conduction, muscle movement and numerous other processes.