Neurotransmitters are the chemical messengers that are released by the neuron to communicate with the target cell or another neuron. These neurotransmitters are stored in small, bubble-like structures called synaptic vesicles. When an action potential reaches the synaptic knob, these vesicles fuse with the presynaptic membrane and release the neurotransmitters into the synaptic cleft, which then bind to the receptors on the postsynaptic membrane, transmitting the signal to the next cell. The neurotransmitters are then either taken back into the presynaptic neuron for reuse or are broken down by enzymes in the synaptic cleft.