Describe how an action potential is carried across a synapse between to neurons.

Once the action potential reaches the pre-synaptic bulb, the change in membrane potential triggers the opening of voltage-gated calcium channels to allow calcium to enter the cell. The influx of calcium triggers the movement of synaptic vesicles, containing a neurotransmitter, to the pre-synaptic membrane. The neurotransmitter leaves the pre-synaptic bulb via endocytosis and moves across the synapse. The neurotransmitter binds to sodium channels on the post-synaptic bulb, which opens them to allow sodium into the post-synaptic neuron. The influx of sodium triggers the action potential in the post-synaptic neuron and allows the action potential to continue down the neuron.