Synaptic Transmission A. Definitions 1. A neurotransmitter is a chemical contained in a neuron which is released by an action potential, crosses the synaptic cleft, and interacts with a post-synaptic target to cause excitation or inhibition of that target. A neuromodulator is a chemical which does not by itself cause excitation or inhibition postsynaptically, but which influences the probability that a neurotransmitter released from the same cell will cause a post-synaptic response. A neurohormone is a substance released from a neuron which travels far beyond the synapse, ie into the blood, to influence the activity of distant targets. GABA, Glycine, Aspartate, Glutamate 3.
Enkephalins are the body's own morphine.
C. Considerable evidence indicates co-localization of multiple neurotransmitters in individual neurons 1. D. Examples of drug sensitive sites in synaptic transmission 1. Microtubules responsible for orthograde and retrograde transport of macromolecules between the soma and distal processes. Electrically conductive axonal membranes. Sites for active reuptake of released transmitters.