Neurotransmission is the process whereby a neuron fires, releases neurotransmitters into the synapse, and the activity of a second neuron is affected. In the presynaptic neuron, neurotransmitters are stored in vesicles present at the axon terminal. In the event of an action potential in the presynaptic neuron, an influx of calcium ions promotes the release of neurotransmitter into the synaptic cleft. The neurotransmitter molecules will bind to receptors at the postsynaptic membrane, and effect the activity of the postsynaptic neuron either by excitation or inhibition. The neurotransmitter molecules still present in the synaptic cleft will then either be broken down or taken back into the axon terminal of the presynaptic neuron, where they will be re-used or disposed of.