While the muscles in your arms and legs might get tired and achy after a workout in the gym, a brisk walk or a spot of energetic gardening, the muscle cells in your heart (two of which are seen here down a high-powered microscope) don’t have that option. They have to keep pumping 24 hours a day, clocking up around 2.5 billion beats in a lifetime. Unlike skeletal muscle cells in the body, which are very long and thin, heart (cardiac) muscle cells are shorter and Y-shaped, locking together and keeping in close contact so they move as one. There’s another important difference: once they’ve contracted, squeezing blood out of the heart, cardiac muscle cells take a relatively long time to get ready for another beat. This means they can’t stay contracted – unlike skeletal muscles, which can hold a pose for a long time – keeping the heart beating regularly.
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.
BPoD is also available in Catalan at www.bpod.cat with translations by the University of Valencia.