Final answer:
Cardiac pacemaker cells and contractile cells have some similarities in their action potentials, but also some important differences.
Step-by-step explanation:
Cardiac pacemaker cells and contractile cells have some similarities in their action potentials, but also some important differences.
In pacemaker cells, the resting membrane potential is around -60 mV. This potential gradually rises due to a slow influx of sodium ions, leading to spontaneous depolarization. Once the threshold is reached, voltage-gated calcium channels open, leading to a rapid influx of calcium ions, causing further depolarization. This is followed by repolarization due to the opening of potassium channels.
In contractile cells, the resting membrane potential is much more stable at around -90 mV. When stimulated, voltage-gated sodium channels open, causing a rapid depolarization. This is followed by a plateau phase where calcium ions enter the cell, maintaining the depolarization. Finally, potassium channels open, allowing repolarization.