= Solution
<Ion-channel deactivation> and <ion-channel inactivation> are different. <Ion-channel deactivation> closes an activation gate when the <voltage> returns toward rest. <Ion-channel inactivation> makes a channel unavailable even while depolarization remains favorable for activation. A minimal kinetic picture is a closed state, an open state and an unavailable state, with recovery required before reopening. This helps terminate inward <electric current> and produces a <neuronal refractory period>.
In rapid <voltage-gated potassium channel> <N-type inactivation>, a cytoplasmic terminal segment, sometimes supplied by an auxiliary subunit, blocks the open inner pore. The classic <ball-and-chain inactivation> picture is supported by loss of rapid <ion-channel inactivation> after removing the relevant terminal segment and restoration by an appropriate soluble <peptide>. This links a mobile structural element to open-pore blockade; it does not imply that all <potassium> channels use that mechanism.<Restoration of inactivation in mutants of Shaker potassium channels by a peptide derived from ShB by William N. Zagotta and others>[1990 primary study, restoration of rapid inactivation]{ref}
Slower <C-type inactivation> involves rearrangement near the <selectivity filter> and external pore. Dependence on pore structure, <ion> occupancy and extracellular <ions> distinguishes it from a simple cytoplasmic plugging particle. Different channels can combine several unavailable states, so a single recovery <time constant> need not describe every trace.
Fast <ion-channel inactivation> in canonical animal voltage-gated <sodium> channels involves the intracellular linker between domains III and IV, including its hydrophobic IFM motif, and is coupled to domain-IV voltage-sensor activation. The modern structural interpretation is an allosteric latch acting on the gate, rather than a universal literal particle sitting in the <ion> pathway. The older hinged-lid analogy is useful only with that qualification.https://www.nature.com/articles/s41467-022-30400-w/[2022 primary structural study, discussion distinguishes IFM-mediated allosteric inactivation from an observed alternative N-terminal pore block]{ref}
Functionally, a <voltage clamp> trace shows <electric current> declining during a maintained step; a second test pulse measures recovery of availability. Holding-potential dependence separates an altered fraction of available channels from a mere change in maximal open <electrical conductance>. Persistent <electric current> after defective <ion-channel inactivation>, or delayed recovery that reduces subsequent responses, illustrates why both entry into and exit from unavailable states matter for excitability. A decaying macroscopic <electric current> alone does not uniquely identify the molecular mechanism.
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