Supplementary Video 2. Panel A contains motion-corrected volumetric image data obtained from the V1 region of the cerebral cortex (130 × 130 μm2, from the surface to 60 μm below) with a customized miniature two-photon microscope, from the brain of a live Thy1-GFP transgenic mouse, as it stepped down a ladder. Panel B contains a remarkably similar recording of Calcium transients detected in SAN tissue preparation extracted from a HCN4-GCaMP8 transgenic mouse (20× water immersion objective). Panel C depicts a panoramic (5× air objective) recording of Calcium transients across the entire HCN4+ meshwork. Note how the earliest Calcium events become visible near the central body of the SAN, and continue to appear in other locations towards the inferior and superior venae cavae. Panel A adapted from Zong et al., 2017); Panel B adapted from from (Bychkov et al., 2020); Panel C adapted from (Bychkov et al., 2022).