The word of the week this week is one that many scientists often assume that you already know: presynaptic. But do you? Pre- means before, and it's before the synapse, but what does that mean?
Presynaptic: This is an adjective really, but when I use it, I use it to talk about the neuron that releases the neurotransmitters into a synapse. A synapse (by which I usually mean the synaptic cleft technically) is a space between two neurons, through which chemicals pass to transmit a signal from one neuron to another. The neuron SENDING the signal is considered to be "presynaptic", while the one receiving the signal is "postsynaptic".
This word is very dependent on context. Neurons receive and send information, often in the same area, so whether you are looking at a presynaptic neuron depends on what neurotransmitter or modulator you are looking at, where the signal is coming from, and where it is going. Often a neuron is presynaptic in many places while being postsynaptic in many others, or even within the same signal, as it sends signals back.