How does the heart keep rhythm?

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I know electrical signals are sent causing it to contract, but what sort of internal clock is this? What causes it, and how is it so exact?

In: Biology

Most cells in your body have a “resting membrane potential” in which they’re ready to send an electrical signal but they need a trigger to tell them when to fire. The pacemaker cells in the heart don’t have a resting membrane potential, they send that signal as soon as soon as the cell reaches threshold potential. The charge needed to send the signals is dependent on the movement of electrolytes so that is what determines how quickly the heart beats.

The best analogy I can think of is one of those bamboo shoots that fills with water and then tips over when it’s full. Think less water when you’re relaxed and more water when you’re excited. The rate may change but the rhythm will remain constant.
Sorry if it got too medical, I don’t think you could explain this to a 5-year old lol

The thing that differentiates the heart cells is something called the ‘funny current’. Usually channels of excitable cells open when they become positive but the funny current channels open when the cells are negative. Essentially this means that channels open and the voltage goes up and then falls back down but when it falls down the funny current makes it go back up etc

Edit: in an attempt to make this 5 year old friendly, consider an analogy of someone throwing a ball in the air. They have to put the work in each time to throw it in the air. In comparison a ball bouncing on a trampoline (without air resistance etc) would go up and down forever with extra work being put in.