Week 3. Synaptic Transmission and its wonders

This week was full of interesting information about the process of information transfer at a synapse. During the lecture, we learned about electrical and chemical synapses. In a mature human system, the majority of the synapses are chemical. Now we know that there are three main types of neurotransmitters involved in chemical synaptic transmission: Amino acids, amines, and peptides. Neurotransmitters have different sizes and are stored at particular places: amino acids and amines smaller in size than peptides and stored in synaptic vesicles, peptides located in secretory granules. It seems quite complex that even one neurotransmitter might be excitatory or inhibitory depending on which type of receptor it binds to on the post-synaptic membrane. The complexity and finesse of the synapse, and how precisely everything seems to work is quite mind-boggling!

The two different kinds of receptors on the post-synaptic membrane are ionotropic (ligand gated ion channels, they open as the neurotransmitter binds to them and depending on which kind of ions it allows to pass to the post-synaptic cell, it will either cause excitatory (with influx of + ions) or inhibitory (- ions) potential); and metabotropic (with the neurotransmitter binding to them they will activate a second messenger which in turn can make the ion channels more or less active or change the activity of proteins inside the neuron); in the case of the metabotropic channels the response of the target cell occurs more slowly then in the case of ionotropic channels

Among neuronal transmitters and their synthesis, release, and recovery we also learned about synaptic integration. Neurons send and receive signals from many other neurons. The integration of all inputs obtained by postsynaptic cells determines their actions. Both excitatory and inhibitory input decay with time and distance,  but eventually might reach the trigger zone. Temporal and spatial summation is needed from many excitatory inputs in order to make the neuron fire. If the summation of all the excitatory and inhibitory potentials bring the membrane potential over the threshold value, then an action potential would be started at the trigger zone, traveling all the way down the axon. There can be fine-tuning of the output of the neuron on multiple levels, from dendrite to the soma and to the axon terminals.

The main difficulty we had and still have during the course is the amount of information we should remember each week. Even if the book and lectures are attention-grabbing, it is sometimes hard to remember everything and understand which parts of the information are the core ones.