The propagation of impulses is explained by ionic permeability mechanisms in the axon membrane. Two different types of ionic channels, sodium channels and potassium channels, open and close in the membrane in response to changes of the membrane potential. Open channels allow ions to pass in or out of the axon at high rates as though the channel is a pore. Many neuropoisons and neuropharmacological drugs act directly to block, open, or in other ways change the properties of the ionic channels. The nature of the ionic channels in the axon seems to be the same in invertebrates and vertebrates.
Bertil Hille. Ionic Permeability Changes in Active Axon Membranes. Arch Intern Med. 1972;129(2):293–298. doi:10.1001/archinte.1972.00320020137011