Sara J, a 16 year old female from the Internet asks on October 6, 2001,What causes a human embryo heart to begin beating? And when a cell divides does it "spark"?
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The heart develops in a human embryo around day 23.
As for what actually causes the heart muscle to contract at all, one needs to first understand that an electric potential is created in all of your muscle cells. The potential is created by ions moving into and out of the individual cell membranes. The response to this activity is contraction and relaxation of the cells as a group. This is how your muscles, composed of many individual cells, work to form a single muscle activity. If you want to understand more about how ions move into and out of different types of muscle cells (there are three types: smooth muscle, skeletal muscle and cardiac muscle), here's a detailed explanation.
As for a cell causing an actual "spark" while dividing.....well, it's not that quick. It takes cells several minutes to divide completely. Chromosomes must be separated, the cell membrane must start to close in on the cell, etc. The general mantra for cell division (mitosis) is IPMAT- interphase, prophase, (prometaphase), metaphase, anaphase and telophase. With so many phases, there isn't a single quick spasm of cell separation. There's lots of info out there on mitosis.
I hope that this has given you at least a place to start with learning more on these topics.
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