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It does so by contracting around 70 times per minute.
In order for cardiomyocytes to contract, they first need to depolarize.
Depolarization is when ions move across the membrane of a cell, and the membrane potential becomes less negative or even slightly positive.
Think of a really pessimistic negative cell throwing his hands up and enjoying a moment of joy.
When one cell depolarizes enough - it can cause some ions like calcium to flow into neighboring cells and trigger them to depolarize as well.
If one cell after another depolarizes, then there’s a depolarization wave which you can imagine would look like a wave moving through a crowd at a football stadium.
So if depolarization waves are going through about once per second, that means that your heart beats once per second, or sixty times in a minute.
Now let’s zoom in on a cardiomyocyte.
When ions like calcium move from that cell into a neighboring cell, this triggers depolarization, and cardiomyocytes depolarize one after another.
Another feature of cardiomyocytes are passageways called transverse tubules, or T-tubules.
Contractility is the ability of the heart muscle to contract and thereby pump blood. Cardiac contractility is determined by the interaction between intracellular calcium concentration, and the myofilament cross-bridge cycling. The Frank-Starling mechanism is a key factor in determining cardiac contractility. This mechanism states that the more stretched (tensed) a heart muscle fiber is, the more calcium it will release from its stores, leading to increased contraction force.
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