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Muscle innervation

Which muscles do we voluntarily control? Which muscles do we have NO control over? What's the difference between sympathetic and parasympathetic innervation? Learn about how our brain splits its control over the body into autonomic and somatic nervous systems.  By Raja Narayan. Created by Raja Narayan.

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Video transcript

So there are muscles that we control, and then there are muscles the control us. So in this video we're going to be talking about voluntary versus involuntary muscle control. And then I'll talk about the autonomic versus the somatic nervous systems, and we'll jump into a few of the subunits of those systems as well. So imagine if we had this gentleman right here, who does not look very impressed. We can talk about what parts of our nervous system are responsible for voluntary control of muscles versus those parts of the nervous system that are responsible for involuntary muscle control. Now, the first question that should come to your mind is why do we have this sort of a setup? Why is it important to have things that are involuntarily contracting? Well, think about structures in our body that we don't actively think about. We have the heart, so we've got things like cardiac muscle. We've also got things like our intestines, so that's composed of smooth muscle. Smooth muscle is also found lining our vessels whenever we need to vasoconstrict, or narrow those vessels. So there's also that smooth muscle there. So we don't think about whether we need to divert blood away from our skin towards our abdomen or towards our brain. Our body just does that for us, and that's muscle that's controlled on an involuntary basis. What about on the flip side over here? For voluntary control, which of the three types of muscle do you think is under voluntary control? Well, if you said skeletal muscle, striated skeletal muscle, you'd be absolutely correct. So that's how we split that up. Now, what parts of our nervous system here do we use for voluntary versus involuntary control? I'll start on this side. So what we have drawn here, this person who's not very impressed, is the brain as it goes down into the spinal cord. This general area is referred to as the cortex, the cerebral cortex. And that's part of voluntary control of muscle. In addition to that, we've also got what I can call the cord, over here, the spinal cord. And that'll also be contributing to voluntary control of muscles. And the way I like to remember this is that if it's something that's controlled by me, if I am the one that controls the muscle function, then I'm going to use either my cortex, which also happens to start with a C, or my cord, which happens to start with a C. So if it's controlled by me, or if it's voluntary, that's going to be the cortex or the spinal cord that comes in handy. Now, what about if we're talking about involuntary control? This part that I'm going to draw briefly that sits back here behind the spinal cord and then goes in there, that guy is called the brain stem. And so the brain stem is responsible for things like if we should have more blood go to our abdomen instead of our skin, so if we should dilate smooth muscle in our arterioles or if our heart should beat faster. The brain stem will regulate that through parasympathetic or sympathetic mechanisms we'll talk about in a minute. In addition to the brain stem, there's a structure that's found down here that contributes to involuntary control, but it's not in the spinal cord. It's actually beside the spinal cord, and it's lined like a chain. So I'll draw it like this with these sort of cell bodies, this neuronal tissue with cell bodies that sit outside of our central nervous system in a chain. And so this is called sympathetic ganglia. Well, what the heck are ganglia? It sounds like it's plural for something. Well, let's define that, sympathetic ganglia, or just a ganglion if we're going to use it in a singular term. A ganglion is just a cell body or a soma of a neuron that sits outside the brain and spinal cord. I'll just write brain right here. And most of these ganglia sit besides the spinal cord. So that's an important point, the sympathetic ganglia that sit beside the spinal cord. And so that comes with another trick that I'd like to think about when I'm trying to remember which parts of my nervous system is responsible for involuntary control. This is stuff that's going on that's beyond me. It's beyond my control. And so if it's beyond me, I'm going to have to use either the brain stem or neuronal tissue that sits beside the spinal cord in order to be able to cause involuntary contraction of muscle. So great. That's voluntary versus involuntary control.