In the fifth lecture we talked about neurotransmitter systems. There are more than 100 different neurotransmitters and some neurotransmitter candidates. The major classes of these are amino acids, amines and peptides. To be called neurotransmitter, there are three conditions that has to be filled: it need to be synthesized and stored in presynaptic neuron, needs to be released from the presynaptic axon terminal following stimulation and need to produce a response in the postsynaptic cell.
We went a bit deeper in the function of synapses than previously in this course. The transmitter system can be divided into chain of events. The neurotransmitters are synthesized by the synthesizing enzymes and transferred to vesicles by vesicle transporters. This all happens in the presynaptic axon terminal. After releasing these neurotransmitters they can be reuptaken or degraded by degradative enzymes. In the postsynaptic membrane there are receptors, transmitter-gated receptors and G-protein-coupled receptors. They affect directly on the ion channels, either opening or closing them, or they can work as a signal cascade through G-protein-coupled receptors. The G-protein-receptors activate the G-proteins, which then again activates the effector enzymes (like adenylyl cyclase in case of ACh). Effector enzymes use ATP to create second messenger cascade which leads to opening and closing many ion channels. This one G-protein-coupled receptors affecting on many ion channels is called signal amplification. These opening and closing of channels have an excitatory or inhibitory effect on the postsynaptic dendrite. Finally, we learned about the different types of neurons depending on which neurotransmitter they use: catecholaminergic, amino acidergic, serotonergic, cholinergic neurons.