What’s happening neurologically/biologically/chemically for your heart to speed up or slow down say exercising or when stressed? What’s the key contributors?
In: Biology
Your heart rate is actually governed by a few different systems.
Firstly there is something called the sinoatrial node which pulses regularly. This pulse occurs because there is a special movement of charged chemical ions that pass from one side to another of the cell (the “funny” current). Thus means the cells have automaticity – basically without any other influence at all they will regularly pulse and cause the heart to beat. This property is pretty unique to heart electrical pathway cells.
If the sinoatrial node is damaged, more areas downstream will take over, though the further you go down the path the slower the basic rate will be. E.g. the atrioventricular node is usually the next one in line to take up the slack.
When each pulse occurs, it travels down the electrical pathway and the heart muscle contracts (assuming the heart is working fine).
In response to different stimuli however, the rate that this all occurs will change. Usually part of your nervous system called the parasympathetic system is in control. It keeps the rate fairly steady and low. E.g. 70 beats per minute.
In response to potential issues, the sympathetic system activates e.g. when you suddenly hear a loud noise. This overrides the parasympathetic system and you get an increase in heart rate and strength of beat. Other parts of your body will also respond e.g. pupils dilate, you sweat, you increase.blood flow to your muscles. All this is possible due to rapid release of chemicals called catecholamines, for example adrenaline, which stimulate loads of different parts of your body.
We can replicate both the parasympathetic (chill out) and Sympathetic (emergency mode) with many different drugs that act on the same receptors.
Please bear in mind this is an oversimplified version because ELI5.
Source- I work in intensive care.
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