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  1. A nerve impulse is a wave of propagation of an action potential that moves through a nerve cell in the form of a change in the potential on the neuron membrane.

    Initially, its membrane from the extracellular side has a “+” charge due to the large number of cations Na+ in the extracellular fluid and intracellular — “–” due to the large number of negatively charged protein particles that are too large to leave the cell (classically considered outside cells are sodium (and chlorine) because the primary broth in which formed the first cells on Earth were salty and contained more precisely NaCl). This state is called the resting potential.

    The action potential is the reverse change of the membrane potential: outside it becomes “–”, and inside it becomes “+”. This is due to some kind of stimulus: in the worst case-a violation of the cell envelope and the exchange of cell ions with the intercellular environment, in the best case — the interaction of certain substances with the receptors of the postsynaptic membrane in the synaptic cleft, which leads to the activation of these receptors and the opening of channels for sodium and potassium, which leads to their exchange between the intracellular and extracellular environments.

    In the future, ion channels for sodium and potassium begin to open like an avalanche, following a wave of sodium ions flowing into the cell (a change in the potential at the previous site causes a change in the next one, and so on without stopping from the beginning of the neuron to the end-from the dendrite to the axon). The wave propagates in one direction, because previously activated channels cannot be activated again for some time.

    Thus, a nerve impulse is the same electric current through wires, only the current of charged ions through nerve cells.

    If you don't understand something, please write in the comments and I'll update my answer.

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