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.
Written by Kat Arney
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