<prompt> Post-tetanic potentiation is due toHyper polarization of muscle fibresRapid K effluxIncreased availability of CaRapid Na influx  <response>: Post-tetanic potentiation one form of plastic change it is the production of enhanced postsynaptic potentials in response to stimulation. This enhancement lasts up to 60s and occurs after a brief tetanizing train of stimuli in the presynaptic neuron. The tetanizing stimulation causes Ca2 to accumulate in the presynaptic neuron to such a degree that the intracellular binding sites that keep cytoplasmic Ca2 low are overwhelmed. Ref: Ganongs Review of Medical Physiology 26th edition 