if you look at a diagram of the nervous system one thing that you'll notice is that everything is connected they have to be connected so the information can pass between different parts of your body but one thing that we do when we study science is break things up into different divisions or different parts that we can study individually when we do this it helps us better understand how does the system work how does it function and do what it needs to do so in this video we're looking at the divisions of the nervous system so even though the nervous system is one large complex network we're going to break it up into its individual parts and study them separately in order to better understand how it all works together let's jump to the whiteboard my favorite way to think about the divisions of the nervous system is to think of them in terms of information coming in us processing that information in some way and then doing something with that information in my homeostasis video i took us through a similar process where i had a sensor an integrator that's where we processed some information and then an effector where we made some change to bring a variable back to the set point during a homeostatic negative feedback loop like that we use all of these divisions of the nervous system as part of the process on the bottom left here we have receptors above that we have the peripheral nervous system which includes all the nerves that branch out of the brain and the spinal cord at the top of our diagram we have the central nervous system and that is the brain and the spinal cord and then in the bottom right of the diagram we have effectors effectors are all the different organs in our body that can produce some response to information that we brought into the body i think of our sensory receptors in two main categories one are the things that we can consciously detect those would be our special senses like seeing or hearing or tasting or feeling things like detecting cold or detecting pressure we often call those our special senses or our five senses and the second type i think of are the visceral receptors these would be receptors throughout your internal organs monitoring things like your blood pressure the stretch in your stomach or your blood sugar levels things like that as these special sensory cells throughout the body detect information they're constantly sending signals through part of your peripheral nervous system called the sensory division the sensory division is taking information from your sensors or your receptors and sending that information toward the brain and the spinal cord that's all taking place in these nerves that we have drawn in the diagram right here the sensory division is also called the afferent division not to be confused with the efferent division afferent and efferent really yeah kind of confusing because those two terms afferent and efferent are really easy to get confused i refer to these two divisions as the sensory division and the motor division the sensory division bringing information to the brain and spinal cord and the motor division taking information from the brain or spinal cord and sending it out to effectors throughout the body since both the sensory division and the motor division exists in the nerves that run between our brain and spinal cord and the rest of our body they're both considered part of the peripheral nervous system whenever you think of nerves in the body think of the peripheral connecting the two divisions of sensory and motor is the central nervous system which includes your brain and your spinal cord the brain and the spinal cord are the main organs for taking information and previous experiences and making decisions about what to do next this could be consciously controlled like things that you think about doing or it could be subconsciously controlled such as a quick reaction to something or an implicit bias or regulating your heart rate things that you don't actively think about so as information comes into the brain and spinal cord from that sensory division your brain or spinal cord will process or integrate those sensory inputs and make decisions about what to do once the decision has been made the brain or spinal cord will send information out through the motor division to cause the change to happen in the body this motor division or efferent division of the nervous system has two parts to it the somatic division and the autonomic division the somatic division is going to control your skeletal muscles i think of somatic and skeletal this is all voluntary things you can voluntarily control the movements of your body so if you make a decision to go run or if you make a decision to sit down and stop procrastinating on your schoolwork or to get up and do a silly dance you're making conscious voluntary decisions using your skeletal muscles so this will be part of the somatic division of the nervous system the opposite of that is the autonomic division of the nervous system autonomic sounds like automatic so these are going to be processes that happen subconsciously or automatically or involuntarily you don't think about these things occurring they're happening in your subconscious in your brain humans generally aren't able to consciously control their autonomic division of their nervous system these are all processes happening subconsciously or automatically these neurons in the autonomic division are going to send signals down to involuntary organs throughout our body in just a minute we're going to see a whole bunch of examples of this now this autonomic division has two divisions of its own i know there's a lot of divisions here our country is just so divided these days much like our nervous system does that comparison work i don't know those two divisions of the autonomic nervous system are called the sympathetic and the parasympathetic and before we dive into the difference between those two subdivisions of the autonomic nervous system let's recap everything so far we have sensory receptors such as the visceral receptors throughout our body or our special senses like touch and taste and sight and smell that are collecting information and it's being sent through the sensory division or afferent division of the nervous system up to our brain or spinal cord our brain or spinal cord which is the central nervous system will process that information and make decisions about what to do signals are then sent from the brain or spinal cord through the motor division of the nervous system to cause some change to happen in the body the sensory and the motor division both take place in the nerves of our body and so they're both part of the peripheral nervous system the motor division has two parts we have the somatic which controls voluntary movement of our skeletal muscles and the autonomic division of the nervous system which controls automatic or involuntary processes like regulating blood pressure and blood sugar and things like that so now let's take a deeper dive into the autonomic nervous system into the sympathetic and the parasympathetic the sympathetic division of the autonomic nervous system controls your response to stress i remember sympathetic and stress because they both start with an s think of a time where you were stressed out you had a big test coming up that you were nervous about you're finally worked up the courage to tell that person that you really like them like like like them you're walking down a dark alley and you hear somebody come up from behind you whatever the situation is that you've been in that made you stressed our bodies respond in the same way so everything you see in this left column will be things that your body does whenever you're undergoing stress now stress isn't a bad thing stress can be good stress can keep us safe when we're in a dangerous situation it's all about our bodies responding appropriately to the given situation this sympathetic response we call the fight or flight it gets that name because a lot of times it's going to cause us to fight back against something or to maybe run away from something the opposite of this is the parasympathetic division of the autonomic nervous system the parasympathetic is all the things that your body does whenever it's relaxed whenever it's calm cool and collected yeah this is often referred to as the rest and digest response so everything you see in this right column are going to be the things that happen whenever your body's calm and not under any stress so let's go through a bunch of examples these first examples are going to be processes that are amplified whenever you're under stress our heart will start beating faster and harder whenever we're under a stressful situation during the sympathetic response we need our heart to beat faster because we need to get oxygen and nutrients throughout our body to power our muscles so that we can run away so we can fight back so that we can be prepared for whatever we need to do compare that to a parasympathetic response when we're relaxed our heart beats slow and softer another sympathetic change is that our airways will expand this allows us to breathe more to breathe faster and to get more oxygen into our bloodstream to power our muscles so that we can run away or whatever we need to do to survive under parasympathetic stimulation our bodies are relaxed and we don't need to breathe as hard or as quickly and so those airways will constrict a little bit they don't need to be quite as wide open another response to the sympathetic nervous system is the dilation of your pupils this allows more light to get in so you can more easily determine what's happening around you and you can stay alert and keep away from whatever might harm you when you're relaxed though your pupils will shrink and they'll let less light in because it doesn't matter as much that you see every single thing going on you're in a safe environment under stressful situations generally your alertness will increase these are all the feelings of being afraid or scared and you're not in a safe situation and you need to get out of that situation so your brain will be on full alert you're going to notice every little thing that might happen and you're ready to make a run for it if you need to compare that to parasympathetic alertness doesn't matter as much you're gonna be able to fall asleep easier things like that during stressful situations a lot of times you'll start to sweat a little bit more your palms might get sweaty before you tell that person that you really like them but during parasympathetic stimulation your hands stay nice and dry now all five of those sympathetic responses are things that our body needs to do whenever we're in danger evolutionarily this might mean that there's a predator about to eat us and we have to be ready to get away or to fight back the next three responses though are examples of things that aren't very important when we're in danger and so these responses are amplified whenever we're relaxed and calm and under parasympathetic control the first one is our digestion think about it you just ate a big meal and then how do you start to feel oh my gosh i ate so much i'm in a food coma why do you get sleepy after you eat well your body is going to devote more resources to getting nutrients from that food and so you start to feel sleepier but whenever you're stressed out and in danger your body's not going to donate resources toward digestion you don't need to get nutrients right now you need to not die or not fail your anatomy test another example is our immune response if an organism is fighting for its life it doesn't need to worry about viruses and bacteria and finding out pathogens at the moment right then it needs to worry about staying alive in the moment but after that organism is no longer in danger suddenly immune system is very important and the body needs to donate resources toward fighting off any bacteria or pathogens or things that might have gotten into the body but during stress forget about it it's not the most important thing right now another example is sexual function sexual functions generally increase when an organism is relaxed and calm and not in danger but when somebody's in a dangerous situation or they're feeling stressed or uncomfortable for some reason sexual activity generally is diminished this is not a comprehensive list of different sympathetic and parasympathetic responses there's a lot more than this the key takeaway in all of this though is to know that your sympathetic response is the stress response and these are the things that happen that keep an organism alive in the moment when they're in danger and then the parasympathetic is the opposite these are the responses that the body has whenever things are relaxed and calm and the organism is not in a stressful situation so these were the divisions of the nervous system it's one system that's all interconnected whenever we break it down into these different parts it helps to understand what's going on a little bit better [Music] neurons in the brain