An action potential is moved along a neuron fiber called the axon through neural pulses that use polarity/charge. The resting potential is the initial state where the outside of the membrane retains a positive charge and inside retains a net negative charge, preparing for the action potential. The beginning of the action potential occurs with depolarization, where the sodium ions that made the outside positive move across the membrane to equalize the net charge, resulting in that spike of positive charge. After the spike has occurred, positive potassium ions that were within the membrane flow out to equalize the charge, resulting in the drop from the spike. The more-negative after potential is when potassium and sodium ions switch to reset back to the resting potential along with the rapid effect of becoming negative again. After this process, the neuron is prepped to fire again. The action potential moves along the axon like the force given to a whipped rope or a wave. The myelin sheath allows the action potential to fire 10x faster, as it helps retain the charges on the axon from other forces. 

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How the neuron determines to fire an action potential in the first place is decided by the dendrites of the cell. When enough stimulus is given to the dendrite of a cell, the cell body makes up its mind to fire a signal through the axon to another cell, muscle, organ, etc. How the dendrite gets stimulated happens either by a specific function to sense the environment or by receiving messages from the axon terminal of other neurons. How two neurons communicate is through the sending of a few thousand molecules known as neurotransmitters, between a gap called the synaptic gap. The neurotransmitters are released from the presynaptic membrane once an action potential is received from the axon terminal, and then received by the postsynaptic membrane from the dendrite of the other neuron. Once enough neurotransmitter gets accepted, the dendrite will fire the message to the cell body, to then send to the axon and do the same process passed on. Enough neurotransmitter has to be accepted in order for the dendrite to consider passing the information, because at the same time other signals are being sent and the highest in quantity gets the message through.