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Sometimes in medicine, you'll see that words get used a lot

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and sometimes the meaning is pretty simple or straightforward and you know can be understood,

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but the words themselves can be kinda tricky and confusion. I think some of that has to do with the fact

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that these words in medicine often come from latin and so we haven't really changed the word and so,

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because latin is not a language that any of us are really familiar with and it ends up being that the term has become confusing.

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So what I'm going to do is, I'm actually gonna lay out four words for you. Starting with Chronotropy.

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And we're going to go through them one by one, basically describing what they mean.

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Chronotropy refers to the heart rate. Now as you see I've put in parentheses, a simpler way to think about these terms.

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So chronotropy has to do with heart rate. A second term is Dromotropy. And Dromotropy has to do with conduction velocity.

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How fast a signal is going from one cell to the next. And then we have Ionotropy - and Ionotropy has to do with contractility.

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How hard the muscle is contracting. The force of contraction, you can think of it as the force of contraction.

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And Lusitropy. Lusitropy has to do with the relaxation - how fast its relaxing. So, lets go through these one at a time and

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talk about the effects of the sympathetics and the parasympathetics on this. So, actually - the other thing I'm

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going to do maybe even write out where these things are primarily being effected. Where and then we'll talk about

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sympathetics and parasympathetics. Ok so where is the first one happening? So we talked about chronotropy. Of course

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its not just one cell that's going to be affected, but in general what cluster of cells are we thinking of? You're right if you're

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thinking about the SA node. Right, the SA node and this is where the heart rate is usually set. And sympathetics are

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usually going to make the SA node go and fire faster because they're going to want to allow more sodium into

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those cells, so its going to get up to the threshold for an action potential more quickly. And parasympathetics

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basically do the opposite right, they're going to let less sodium flow in, and its going to take longer to get to the

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threshold potential. So what about Dromotropy? This is a word that's maybe less commonly used, and that's why I

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want to throw it up so that you're at least familiar with at least the fact that it exists. But dromotropy has to do with

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conduction velocity so how fast is the signal being conducted through the heart. And remember for this

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the major delay ends up being in the AV node right. The huge delay sometimes, we say its a tenth of a second is in

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the AV node. So what happens in the AV node with sympathetic stimulation, well you remember when you're

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sympathetics are around they allow the calcium to come into the cell more quickly, so you actually have a faster