Final answer:
The statement regarding ion channel activity during the plateau phase of an action potential is true. Voltage-gated Ca²⁺ and K⁺ channels are open, while the voltage-gated Na⁺ channels are closed.
Step-by-step explanation:
The statement that during the plateau phase voltage-gated Ca²⁺ and K⁺ ion channels are open, and voltage-gated Na⁺ ion channels are closed is true.
The plateau phase occurs after the depolarization phase, which is marked by a rapid influx of Na⁺ ions through voltage-gated Na⁺ channels, raising the membrane potential to approximately +30 mV. These Na⁺ channels then close, and this depolarization is followed by the plateau phase.
During the plateau phase, slow voltage-gated Ca²⁺ channels open allowing Ca²⁺ to enter the cell, meanwhile, only a few K⁺ channels are open, allowing K⁺ to exit the cell, which slows the decline of membrane potential.
This results in the characteristic plateau seen in the action potential of cardiac myocytes, making the phase crucial for the prolonged contraction needed in heart muscles.
The plateau phase lasts approximately 175 ms, after which Ca²⁺ channels close, and more K⁺ channels open leading to repolarization of the cell membrane.