Final answer:
The voltage-gated channel is the type of channel that has an 'inactivation' phase, in which the channel cannot be reopened immediately after being activated. This mechanism is crucial for the function of excitable cells, including neurons and muscle cells. The correct option is b.
Step-by-step explanation:
The type of channel that has an 'inactivation' phase is the voltage-gated channel. These channels are key components in the generation and propagation of action potentials in excitable cells like neurons and muscle cells. Voltage-gated channels respond to changes in membrane voltage and after activation, they momentarily become inactivated, during which time they cannot be opened again. The most well-known examples of these channels are the voltage-gated sodium (Na+) and potassium (K+) channels.
When a voltage-gated channel opens, it allows specific ions to flow across the membrane, either into or out of the cell, based on the gradient and the type of ion. For instance, voltage-gated Na+ channels open when the membrane potential becomes less negative, allowing Na+ to enter the cell and contribute to the depolarization phase of an action potential. These channels not only have an activation gate but also an inactivation gate, which closes shortly after the channel opens, thus temporarily preventing any further ion passage, even if the membrane potential remains changed.
Leak channels and ligand-gated channels, however, operate differently. Leak channels are randomly gated and contribute to the resting membrane potential but do not have an inactivation phase like voltage-gated channels. Ligand-gated channels open in response to the binding of specific molecules, such as neurotransmitters, but also lack an inactivation phase similar to that of voltage-gated channels.