What is the term for a neuron located 'upstream' of a synapse?

The term for a neuron located 'upstream' of a synapse is the presynaptic neuron. This neuron sends signals to the postsynaptic neuron across the synapse. In the context of synaptic transmission, the presynaptic neuron is responsible for releasing neurotransmitters into the synaptic cleft, which allows for the communication process between neurons. This signaling is essential for a variety of physiological processes, including reflex actions and the overall functioning of the nervous system. The term accurately describes the role of this neuron in the synaptic transmission pathway.