Resting and Action Potential in Muscle Cells

Resting Membrane Potential

• The resting membrane potential of skeletal muscle is -94 mV.
• The resting membrane potential is maintained due to the constant leakage of potassium ions out of the cell.
• Potassium ions leak down their concentration gradient from inside the cell to outside the cell.
• The outward movement of positive potassium ions leaves the inside of the cell more negatively charged.

Action Potential

• The minimum potential required to generate an electrical signal is -70 mV.
• An action potential is triggered when acetylcholine binds to a receptor on the muscle cell membrane.
• The binding of acetylcholine allows sodium ions to enter the cell.
• The influx of sodium ions causes the membrane potential to become more positive.
• This is referred to as depolarization.
• The peak potential during depolarization is +70 mV.
• At the peak, the sodium channels close, while the potassium channels open.
• Potassium ions leave the cell, causing repolarization.
• The repolarization phase returns the membrane potential to the resting potential of -94 mV.
• The membrane potential may briefly drop below the resting potential, known as hyperpolarization.
• Hyperpolarization is a built-in mechanism preventing overlapping muscle contractions.
• The sodium-potassium pump restores the original ion distribution, maintaining the resting membrane potential.

Absolute Refractory Period

• The absolute refractory period is a time when another action potential cannot be generated.
• This occurs because sodium channels are either open, closed, or inactivated.
• Inactivated sodium channels require time to reset to their original open position.