14. The Autonomic Nervous System
Sympathetic Nervous System
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going to finish up this section by talking about those splanchnic nerves as well as the adrenal medulla. So, as we talked about in our sympathetic division, the preganglionic fibers arise from spinal cord segments t 1 through l 2. What we find is that from t5 down, the majority of those preganglionic fibers are going to be these splanchnic nerves which are nerves that synapse in a collateral ganglion rather than in that trunk. So these collateral ganglion are just ganglia that are further out closer to the effector organs. So these, nerves basically bypass the sympathetic trunk. So they pass through it without ever synapsing and instead they synapse in these collateral ganglia. Now, these nerves mainly innervate the visceral structures of our abdomen, so things like our stomach, our intestines, our liver, our spleen. And what we find with these nerves is that the preganglionic fibers tend to be long and the postganglionic fibers tend to be short. So it's the opposite pattern that we saw in the fibers above t5. So, if we look down here we have our, our spinal cord. Again, we're working from t5 and down with these splanchnic nerves and you can see how these purple preganglionic fibers now have to extend all the way from the spinal cord all the way out to these collateral ganglia, which we have depicted here as these yellow balls. And then they will synapse in those ganglia and then these now relatively shorter, postganglionic fibers just go from the collateral ganglia out to the effector. Okay? So that is what that looks like and, again, it's that opposite pattern from what we saw above t5. Now, next, we're gonna kind of switch gears and just talk about the adrenal medulla, which is a very important structure for our sympathetic division. Now, to understand why this is so important, we have to recall something called dual innervation. And so we've been talking about how our sympathetic nervous system obviously innervates all of these organs. But what we haven't talked about in detail is how most organs are actually innervated by both the sympathetic and parasympathetic divisions and that is called dual innervation. But there are exceptions to that and one of those exceptions is the adrenal medulla which is only innervated by our sympathetic nervous system and for a very good reason. So the adrenal medulla, when it gets stimulated, secretes epinephrine and norepinephrine, which are also known as adrenaline and noradrenaline. And And as I'm sure you can imagine those are very important for that fight or flight response to kick in and get your body really going. And so, that's why this structure is only innervated by our sympathetic nervous system. That parasympathetic division does not want any extra epinephrine or norepinephrine kicking around in your body. Right? That's not going to help you rest and digest. So this is very much a sympathetic structure. So the adrenal medulla is located, in the adrenal gland, which is located right on top of the kidney, kinda like a little hat on top of the kidney. And what's really cool about this structure is that it can actually be considered a modified sympathetic ganglion. So if we look down here at our image we have our adrenal medulla right here and you can see that the way that it's innervated this is just a preganglionic fiber going all the way to this structure and that's because the, the synapsing is actually gonna happen in that adrenal medulla. Again, it's acting kind of like a modified ganglion itself. So it is very unique in that way as well. But, again, very important for this division because it's going to be releasing that epinephrine and norepinephrine, which are essential for that fight or flight response. Alright. So, that was our sympathetic nervous system. Thanks for sticking around and I'll see you guys in the next one. Bye bye.
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