6.2.2 Resting Potentials

Key Features of the Resting Potential

1. Voltage Difference:

• The inside of the neurone has a negative charge relative to the outside, with a typical resting potential of -70 mV.
• This is caused by an imbalance of ions across the membrane.

2. Ion Distribution:

• There is a higher concentration of sodium ions (Na⁺) outside the axon and a higher concentration of potassium ions ($K⁺$) inside the axon.

3. Role of the Sodium-Potassium Pump:

• The sodium-potassium pump actively transports ions:
• 3 sodium ions ($Na⁺$) are pumped out of the neurone.
• 2 potassium ions ($K⁺$) are pumped into the neurone.
• This creates an electrochemical gradient with more positive ions outside the neurone.

4. Membrane Permeability:

• The membrane is impermeable to sodium ions, so Na⁺ cannot diffuse back into the axon.
• The membrane is partially permeable to potassium ions, allowing some K⁺ to diffuse out through potassium ion channels, contributing to the positive charge outside.

5. Imbalance of Charges:

• The movement of 3 $Na⁺$ out and 2 $K⁺$ in creates a net loss of positive charge inside the neurone.
• This makes the inside of the axon negatively charged relative to the outside.

6. Active Process:

• The sodium-potassium pump uses ATP for active transport, maintaining the resting potential.