Artificial Consciousness/Neural Correlates/Synaptic Models/Pre-Synaptic Bud Model

Pre-Synaptic Bud Model
A Synapse, consists of a Pre-Synaptic Bud, a Post-Synaptic sensitive patch, and a gap containing extra-cellular fluid. The pre-synaptic bud, is usually at the end of an Axion process, but some synapses in dendrites have been found to be pre-synaptic buds suggesting that Axons are not the only location for pre-synaptic buds.

Essentially, how the pre-synaptic bud is thought to work, is that as the voltage at the end of the process increases, with the Action potential of the cell, at some point it promotes the secretion of Neuro-Transmitters, this usually happens as a result of vessicles attaching to the cellular membrane at the end of the process. The vessicles release the Neuro-Transmitters into the extra-cellular fluid, where it diffuses across the synaptic gap and can be detected by the post-synaptic sensitive patch.

To complicate this model however, we have to take into account the fact that the voltage, and the attachment of the vessicles to the cellular membrane seem somehow related to the level of Calcium that can be found at the pre-synaptic bud. A condition called Habituation has been discovered where the strength of the connection of the synapse gradually gets weaker, as the calcium levels in the pre-synaptic bud drop, and fewer vessicles attach to the cellular membrane.

This condition is reversed however, with the opening of Synapses like the S synapse or NMDA synapse that pump more calcium into the cell, so that it can be transported to the end of the process. The change in habituation that this causes is called Facilitation. The S type synapse causes short term facilitation, the NMDA type synapse causes Long-Term Facilitation.