Final answer:
Ion channel inactivation refers to closing of the channel even when the stimulus continues, which prevents further ion movement until the channel resets. This occurs in voltage-gated ion channels which are crucial for generating action potentials. A negative ion entering through a postsynaptic channel creates a hyperpolarizing graded potential.
Step-by-step explanation:
Ion channel inactivation refers to B) closing of the channel even when the stimulus continues. This process occurs in voltage-gated ion channels, which open in response to changes in membrane voltage. Their activation is an important part of the action potential. After opening and allowing ions to pass through, these channels become inactivated for a brief period, even if the depolarizing stimulus is still present, preventing any further ion movement until they return to a closed state that can be opened again.
A postsynaptic membrane channel opening that allows a negative ion to enter would create a hyperpolarizing graded potential, making the cell more negative inside and thus less likely to reach action potential threshold. This mechanism operates contrastingly to voltage-gated Na+ channels that, upon opening, allow Na+ to enter the cell and contribute to depolarization, which if reaching threshold, could trigger an action potential.