(3.2.2) Long-term potentiation of synapses
When the postsynaptic cell ignites, receptors on the postsynaptic cell surface increase. In other words, postsynaptic cells ignite with less stimulation than before. This phenomenon is called "long-term potentiation" (LTP).
Since this long-term potentiation finishes in about two hours, we can not explain why we can keep the memory for days by merely this mechanism. However, if stimulated four times at short intervals, long-term potentiation lasts about 28 hours. The shorter the duration is called "Early LTP," the longer one is called the "Late LTP." Interestingly, by chemicals that inhibit protein synthesis, the early LTP is not affected, and only late LTP hindered.
In the early LTP, the cell place receptors previously made and stored on the cell membrane. The process can be accomplished quickly, but it does not last long as the stock of the receiver decreased.
On the other hand, in the late LTP, the amount of receptor itself increase. As the amount of receptors creation increases, the amount of receptor of the cell membrane is kept high for a long time. Protein synthesis inhibitors stop this process because the receptor is a protein.
Fig: - Left: Make receptors a little and put them on the membrane.
- Middle: Early LTP. Put more receptors on the membrane.
- Right: Late LTP. Make more receptors. It keeps large number of receptors on the membrane.
- Middle to Left: 2 hours
- Right to Middle: 26 hours
- Footnote: *13: In the process of protein production, the cell first transcribes the blueprint (DNA) in the nucleus into RNA. Based on that, the cell aligns amino acids, and it goes proteins. This transcription is active when the late LTP is occurring.