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Current time:0:00Total duration:11:24

Video transcript

in this video I want to introduce the autonomic nervous system autonomic nervous system which is part of the overall nervous system and this is a functional division of the nervous system not a structural division like the central nervous system and the peripheral nervous system the autonomic nervous system consists of efferent neurons in the peripheral nervous system that do specific jobs so these are e ferrant neurons and these neurons control 3 different types of cells the first are smooth muscle cells which are in all sorts of structures all over our body like around our blood vessels and the control cardiac muscle the muscle that makes up our heart tissue so cardiac muscle and these muscle tissue types are different than the skeletal muscle the muscle that's all over attached to our skeleton that moves us around because those are controlled by different efferent neurons of the peripheral nervous system those are controlled by lower motor neurons not autonomic neurons the last thing that autonomic neurons control are gland cells some gland cells are controlled by the autonomic nervous system now the autonomic nervous system is called this because it tends to control all these things without conscious involvement it doesn't require the involvement of consciousness to control these things so it's kind of autonomous it kind of does this stuff on its own without our conscious cells having to be involved for the most part and we divide the autonomic nervous system into two big subsystems so let me write two big arrows here and this part we call the sympathetic nervous system a sympathetic nervous system which is the first big part of the autonomic nervous system so I'll just write s and s for short for sympathetic nervous system and this other big part we call the parasympathetic nervous system parasympathetic so I'll just write P and s for short for parasympathetic nervous system and there are a number of big differences between these two parts of the autonomic nervous system that we can talk about in this kind of introductory talk the first big difference is kind of where a start in the central nervous system the sympathetic nervous system starts in the middle of the spinal cord and of the middle part of the spinal cord let me draw a bunch of sohma's here and I'll just take one of these here and I'll draw a little short axon on the first neuron that's coming out of the central nervous system and then it's going to synapse oh the second neuron in a ganglia close to where the first neuron is and then the second neuron is going to send the longer axon to reach its target cell so let me just draw a big T to represent some kind of target cell that it's going to synapse on in this target cell will be a smooth muscle cell a cardiac muscle cell or a gland cell and here's an illustration of kind of the entire autonomic nervous system and here they're showing kind of the middle part of the spinal cord that all these first neurons in the sympathetic nervous system are starting and then there's a short axon til they synapse and a ganglia that's pretty close to the spine here's a set of ganglia in here a few other ganglia but they all tend to be pretty close to the spine this set of ganglia are actually often linked together and kind of a chain which we actually called a sympathetic chain and here's a just a different illustration of the same thing so here it's showing in the middle part of the spinal cord that first axons coming out synapsing in a ganglia close to the spine with a lot of these ganglia linked together in a chain and then the second neuron sending a longer axon out to synapse on the target cell in whatever tissue you're talking about that contains smooth muscle cells cardiac muscle cells or gland cells now the parasympathetic nervous system has its first neurons start in different place in the central nervous system they start either up here in the brainstem or they start way down here at the bottom of the spinal cord and then their first neuron tends to send a long axon out to synapse with the second neuron in a ganglion at a distance from the first neuron and then that second neuron usually sends out a short axon to synapse on its target cell I'll just write a big T here for target cell and here this illustration is showing this as well where it's showing the first neurons of the parasympathetic nervous system either up here in the brainstem or down here at the bottom of the spinal cord and then it's showing these long axons on the first neuron until it reaches a ganglia at a distance from first neuron soma and then a shorter axon on that second neuron until it reaches its target cell and here's another illustration just showing the same thing so here's these first axons coming out of either the brain stem up high or the bottom part of the spinal cord down low and then these first long axons go all the way till they meet ganglion at a distance from the first neuron soma and then the second neuron sends a shorter axon to the target cells so the similarities in the structure of the different parts of the autonomic nervous system are that they both usually consist of a chain of two neurons connecting the central nervous system to the target cell but the differences are where those first neurons start and whether there's a short burst axon and a long second axon or a long first axon in a short second axon but more importantly than these structural differences between the different parts of the autonomic nervous system are the functional differences and these neurons do so many different things and so many tissues of the body that it's a little hard to talk about them in general but there are these great phrases that can kind of help think through lots of the changes that these different parts of the autonomic nervous system do and for the sympathetic nervous system the phrase is fight or flight fight or flight that the sympathetic nervous system when it's activated will cause lots of changes in the body that will prepare to either fight or run away which can kind of help you deal with threatening or dangerous situations so I'll write that in red here for the sympathetic nervous system whereas the parasympathetic nervous system I'll write in a nice cool green here because it it's phrase is rest and digest rest and digest so it when it's active it often causes lots of changes in the body that are more important for homeostasis and just maintenance of the body in non-threatening situations so let's take a few examples of a few tissues where these different responses happen to get a feel for what this means so first let's look down here at the gastrointestinal system the intestines or the gut and both the sympathetic and the parasympathetic nervous system play a role in a lot of activities of the gastrointestinal system but one is what flow to the intestines because the amount of blood flowing through the intestines plays a big role in how much digestion the intestines can do blood flow to intestines and it also plays a big role in how much blood is available for other parts of the body so when the sympathetic nervous system is activated in some kind of fight or flight situation blood flow to the intestines decreases and that blood is actually diverted away from the intestines often to skeletal muscle so all our muscles all over our body that can help us move to deal with dangerous situations the blood is going to leave the intestines and go to that because during a dangerous situation is not the time to be digesting food it's the time to be moving so the blood flow decreases to the intestines and is diverted to skeletal muscle whereas most of the time when you're in a non-threatening situation and it's time to rest and digest the peripheral nervous system is activated and that increases blood flow to the intestines that will divert blood away from skeletal muscle because now you're not in a fight or flight situation and you want to rest and digest so it's going to bring the blood flow back to the intestines to increase your ability to digest food if we look at the heart both the sympathetic and parasympathetic nervous systems innervate the heart and we look at the heart output kind of how much blood the heart is pumping out over any particular unit of time hurt output of blood when the sympathetic nervous system is activated the heart output increases the heart pumps harder and pumps faster and pushes more blood out so that things like skeletal muscle can get more blood flow in addition to diverting blood flow from the intestines to skeletal muscle the heart's just going to push more out so there's more available for the skeletal muscle when the parasympathetic nervous system is activated the heart output goes down the heart is pumping less hard and it's beating less often it's just working less because you don't need as much blood flow to the muscles for movement so you go to kind of a baseline level that's sufficient for activities that involve resting and digesting so these examples of blood flow involve the activity of smooth muscle because smooth muscle is around our blood vessels and determines where the blood is going to flow to and cardiac muscle because the cardiac muscle makes up the heart and then if we think about gland cells there's a bunch of different glands that the autonomic nervous system controls and they tend to be activated kind of differently at different times so one type of gland that's activated during fight-or-flight situations when the sympathetic nervous system is active our sweat glands out here in the skin the sweat glands are activated to secrete sweat which helps cool us down which increases our ability to move faster and farther if we're able to stay cool whereas some glands that are activated by the parasympathetic nervous system include things like the salivary glands that produce saliva in our mouth because saliva is very useful for digestion and it's part of a number of activities that happen that help us digest food so I find these phrases helpful what I'm thinking about what affects the autonomic nervous system will have on different tissues of the body during different situations because like in all of these examples most of the things that the sympathetic nervous system does when it's activated increase the body's ability to turn stored energy into movement to deal with dangerous situations like moving blood from the intestines to skeletal muscle and increasing the amount of blood being pumped around from the heart and increasing sweat production from sweat glands to keep us cool while we're moving to deal with a dangerous situation whereas all of these things that the parasympathetic nervous system is doing make sense in non-threatening situations where we're actually trying to conserve and store energy like diverting blood flow away from skeletal muscle to the intestines Timm increased digestion decreasing heart cardiac output to conserve energy and increasing saliva production from the salivary glands to help with digestion as well but the autonomic nervous system affects many more structures and has many more functions than I can cover in this little introductory video for instance autonomic neurons play a role in changing the size of your pupils in your eyes in sexual responses and in secretion from a whole bunch of other glands and because it does so many different things I find it best act not cover it all in one sitting but instead to cover these things as you're studying each individual organ system because almost any organ system you're going to cover is going to have autonomic neurons coming in and affecting how that organ system functions