Biophysics: Membrane Potential and Voltage

Electrical Circuits

• Voltage plays a crucial role in an electrical circuit, enabling the flow of electric current.
• According to Ohm's Law, the relationship between potential difference (V), current (I), and resistance (R) is V = I × R.
• Current represents the flow rate of electric charge in a circuit.

Resistance and Voltage

• If 12.0 V is applied to an automobile headlight and 250 mA flows through it, the resistance of the headlight is 48 ohms (calculated using Ohm's Law).

Cell Membrane Potentials

• The membrane potential in cells is primarily determined by the concentration gradient of ions across the cell membrane.
• A voltmeter measures the voltage across the cell membrane (inside versus outside) of a cardiomyocyte.
• The resting membrane potential is caused by the concentration gradient of ions, particularly potassium (K+) and sodium (Na+) ions.
• Potassium ions have a much higher concentration in the cytoplasm compared to the extracellular fluid.
• The general rule regarding membrane potential is that a higher concentration of ions inside the cell results in a more negative resting membrane potential.
• The equilibrium potential for a given ion is the potential difference at which the tendency of the ion to diffuse down its concentration gradient is balanced by the electric force driving it in the opposite direction.
• The concentration gradient of ions across the cell membrane primarily determines the membrane potentials in cells.