Pushing and Pulling

The heart is autogenic and depolarizes no less But it can be influenced by the ANS. Autogenic means leaky channels And within the channel annals, This means changes in membrane potential And for the heart, are is essential. The sympathetic speeds it up and the parasympathetic, it slows. And both the sympathetic and parasympathetic talk to the nodes But only the sympathetic to the myocardium goes. A change in rate is chronotropic. A change in force is inotropic. A muscarinic receptor for acetylcholine Opens potassium channels and that will mean That as potassium leaves, it will oppose the leak Of sodium entering and both will tweak The membrane potential so that it’s slower To reach the threshold and not from potassium, go lower. So overall, to reach threshold, it takes longer But the contraction is not stronger. Beta 2 is the receptor for the sympathetic response And norepinephrine it will ensconce. Separate sodium channels will open and add to the leak And faster get to the threshold peak. But norepinephrine binds to the muscle And in doing so, will make it hustle. So overall, to reach threshold, it’s quicker And contraction strength, a stronger ticker. But epinephrine too, has the same effects With the sympathetic flex. Beta blockers which calm the heart Antagonists that will slow the start Bind to these receptors tightly And make the heart beat more lightly.