Final answer:
Neurotransmitter release and depolarization occur when a neuron sends a signal. This leads to a self-propagating action potential along the axon. Afterward, neurotransmitter reuptake clears the synapse.
Step-by-step explanation:
When a neuron sends a signal, a series of events known as an action potential occurs. When the neuron is activated, neurotransmitter molecules are released into the synaptic cleft. These molecules bind to receptors on the postsynaptic neuron and cause depolarization, a decrease in the voltage across the neuron's membrane. If a sufficiently strong depolarization occurs, reaching about -60mV which is known as the threshold of excitation, it will trigger a positive feedback loop. This loop involves the opening of additional voltage-gated sodium channels and the influx of sodium ions, further depolarizing the membrane. An action potential is a self-propagating reversal of the resting membrane potential that travels along the axon. After the transmission of the action potential, there is a phase known as repolarization, where the inside of the neuron becomes more negative, followed by hyperpolarization, a state where the neuron is even more negative than during its resting state. Finally, the neurotransmitter reuptake process removes the neurotransmitters from the synaptic cleft to reset the synapse for the next signal.