Dual Innervation

by Pravin Shukle, MD

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    Now a lot of our organs have dual innervation. Let's talk about dual innervation. And we will use two examples. The first is the iris and the second is the sinoatrial node in the heart. Now in both cases, there is sympathetic activation through either alpha or beta activity. In the eye, the sympathetic system causes a contraction of the radial muscle and dilation of the iris. Now, it's hard to remember that. So let's think of it this way. The sympathetic system is the system that we use to run away from the sabertooth tiger as a cavemen. So you need it to be able to see far and you need it to be able to see in the dark. So what we want it to do with our eyes is we want it to open up the iris so that we can see really really well. So it makes sense that the radial muscle which is the spoke like muscle on the outside of the eye will contract, opening up the iris and it also relaxes the ciliary muscle which is the constrictor muscle of the eye. With respect to the heart, we want a fast heart rate because we are going to be running. So it makes sense that we're going to accelerate the sinoatrial node through the beta 1 receptor. We also will increase the activity of ectopic pacemakers. Now why would we want that from an evolutionary point of view. That's because in case the SA node fails we have other ectopic pacemakers that would pick up the job. The opposite of sympathetic activity is parasympathetic activity. Now in the eye we act through the M receptors or muscarinic receptors causing circular muscle contraction. It also results in iris constriction. So we contract that ciliary...

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    The lecture Dual Innervation by Pravin Shukle, MD is from the course ANS - Pharmacology.

    Author of lecture Dual Innervation

     Pravin Shukle, MD

    Pravin Shukle, MD

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