Action Potential has 4 different stages in which it starts with the resting stage. In the resting stage large negative ions inside the axon gives the inside an overall negative charge at -70; in the next stage called the depolarization stage an incoming message stimulates a section of the axon and channels in the membrane open which allows sodium to flow into the axon and the voltage increases to +30. In the depolarization stage new channels open up allowing potassium to enter the axon which then decreases the charge back to -70; though the charge is back to normal, repolarization causes the next section of the axon to start depolarization. The flow of depolarization commences repolarization in specific sections, which stimulates depolarization in the next section; impulses don’t travel backwards because of the refractory period.

 

The synapse is the gap between the giving axon bulb and the dendrites of the receiving  neuron. When the action potential reaches this area it triggers the release of the neurotransmitters from the synaptic vesicles into the synapse. The neurotransmitters bind to the receptors on the dendrites which leads to electrical changes that can generate action potential and continue the signal. The receiving neuron determines whether or not to send its action potential based on the integration of the excitatory and inhibitory postsynaptic potentials it receives. If the combined effect of the excitatory signals exceeds a certain threshold, the neuron generates an action potential and sends it along its axon, continuing the transmission of the signal to other neurons.