# An Algorithm for Creating a Synaptic Cleft Digital Suitable for Further Numerical Modeling
## 3 Results
The green body indicates an astrocyte with leaflet. The orange domain corresponds to presynaptic neuron and a blue area is equivalent to AZ. The isolines indicate the boundaries retained after different radiuses (**a**) and heights (**b**) of synaptic phantoms \(\Omega_{\text{SP}}\) were used; and (**c**) the full structure of the digital phantom, including a postsynaptic neuron (empty domain) with indication of PSD (magenta). The differences in AZ are presented in Figure 4. The results clearly indicate a profound enlargement and change in the shape of the AZ with an increased radius RSP. At the same time, the height of \(\Omega_{\text{SP}}\) is not a crucial parameter affecting the size of AZ under the same radius. Additionally, although the PSD area is similar, it is not equivalent to the AZ. As follows from Figure 4, there is one remarkable feature of our 3D model--the larger synaptic cleft most likely comes into direct contact with the astrocytic leaflet [47]. This observation correlates with the prominent practical finding that large synapses have increased astroglial synaptic coverage [55]. The leaflet protrusion toward the cleft excludes thick intercellular spaces (tunnels) in close proximity to the astrocyte, leaving only a sheet-like diffusion area, which is also in good agreement with 3D reconstruction data from the rat CA1 hippocampal region [38]. An essential part of the applied algorithm is the adjustment of the astrocytic leaflet and its size to AZ and PSD. The presented method makes it possible to create various types of cradle for the synapse. Conditionally, they can be classified as small, medium, and large. It is intuitively acceptable that a large \(\Omega_{\text{SP}}\) should correspond to a large cradle and vice versa. However, this is not necessarily obvious. For native cases, all types of combinations may be considered. The shape and the size of the leaflet likely depend on the activity of the vesicles and the intensity of convectional diffusion near the cleft. The results of astrocyte leaflet modeling are represented in Figure 5. A notable feature of this part of the algorithm is that the shape and size of the leaflets are determined by the curve traces remaining after Boolean operations with \(\Omega_{\text{SP}}\) and \(\Omega_{\text{j}}\). This simplification allows additional geometrical modification of the domains to be avoided and, at the same time, a smooth and twisted pattern of the leaflet to form. The different shapes of the astrocytic leaflets can be applied in the creation of the final synaptic cleft phantom. It is interesting that the same AZ and PSD may be surrounded by various types of cradle (Figure 6). Geometrically, such variation in the mutual position of the astrocyte/neurons is not prohibited. Moreover, this example can be used to evaluate the biological aspect of synaptic plasticity when re-uptake of the neuromediators may be determined not only by the activity level of transporters. The difference in position of astrocytic leaflets reveals a flexibility of spillover flux regulated by the spatial distribution of the transport system. This process can appear as a part of nervous tissue development or pathological changes.