Control of the ANS - Video Tutorials & Practice Problems

Review of Relevant Brain Anatomy

All right. So in this section, we're gonna be talking about some of the brain structures that work together to control our autonomic nervous system. But before we dive into that, we have a quick video for you just reviewing some relevant brain terminology. So we're gonna start with the hypothalamus, which is arguably the most important brain structure when we're thinking about the autonomic nervous system. And that's because our hypothalamus controls autonomic functions. So it sort of acts like your body's command center for autonomic or visceral activities. So it's gonna control things like heart rate, blood pressure, digestion, arousal, you name it. And what we find is that the anterior hypothalamus largely directs parasympathetic activity while the posterior hypothalamus largely directs sympathetic activity. So one way that I always like to remember that is by thinking that the hypothalamus is kind of like a mullet, you know how a mullet is all like business upfront party in the back, right? So I always think that a hypothalamus is sort of like calm, cool, collected upfront. That's that parasympathetic activation and it's all stressed out and crazy in the back and that's that sympathetic activity. So we have our little hypothalamus in a mullet to hopefully help you guys remember that as well. All right. So, next, we have our brains stem, which I'm sure you guys remember, but that's going to act as kind of a relay um center between our brain and our spinal cord and the rest of our body. And it's gonna contain some nuclei that help control autonomic functions. All right. Next, we have our reticular formation and that is a functional system or kind of a network of neurons and nuclei that's going to regulate both skeletal and visceral muscle activity. And our reticular formation is going to have the most direct influence on autonomic functions. And what we find very generally is that the reticular formation is going to become more active when we have sympathetic activation and it'll be less active when we have parasympathetic activation. And then finally, we have our limbic system, which is a whole bunch of brain structures, right? It includes ar thalamus, hypothalamus, amygdala, hippocampus among some others. And it's very important for the processing and interpretation of emotional stimuli, right? So our AMG our amygdala helps us process emotions. Our hippocampus is where we store long term memory and emotional memory. So if you encounter a stimulus, this system is going to help you, you know, recall if you have any strong memories associated with it, any emotions that you associate with it and help you process the stimulus in that way. So looking down here at our brain, we have our limbic system highlighted in orange and you don't have to know where any particular structures of the limbic system are. For this chapter, just know that in general, it's important for processing the emotional salience of a stimulus, right. So we have our limbic system here in orange. You can see we have our little purple hypothalamus right there in the middle of the um cerebrum. We have our green brain stem and you can see that blue reticular formation kind of running through the brain stem. There, there we go. All right. So that is our review of the relevant brain anatomy and I will see you guys in our next video. Bye bye.

Control of the ANS Example 1

So this question asks us a lesion on the anterior hypothalamus would have the most effect on the blank division of the autonomic nervous system. Now, I can immediately eliminate C and D because somatic and involuntary are not divisions of the autonomic nervous system. So we're left with A and B. Now remember our little trick. A hypothalamus is kind of like a mullet. So a mullet is business upfront party in the back, right? And a hypothalamus up front is calm, cool collected. That's our parasympathetic division and in the back, it handles all that stress. That is the um sympathetic division. So if there was a lesion on the anterior at the front of the hypothalamus, our parasympathetic division would be the most affected by that. So there you go.

Levels of Control in the ANS

OK. So let's dive into how those brain regions can work together to control our autonomic functions. So as I mentioned, the hypothalamus is going to be the main integration center of the A NS. So all of the commands are going to be coming from the hypothalamus. And as and as I kind of alluded to now, the A NS primarily operates in two ways. So the first is maintaining homeostasis and that of course, is a largely parasympathetic response. And it's also gonna be responding to emotionally salient or stressful or threatening events, which is more of a sympathetic response. And these two functions are gonna involve slightly different neural pathways. So this first pathway where we're just maintaining homeostasis, we're gonna have some kind of stimulus coming in. So for example, the hormone levels in your blood, the chemical composition of your blood, um the presence of food in your gut, something like that. And then that hypothalamus will process that and figure out what you know, function do we have to do to get back to homeostasis? So, for example, you know, let's slow down hormone production, let's start digestion, whatever it may be. And then that command will get sent to the brain stem to the reticular formation and then down to the spinal cord where that nerve impulse will then travel along the efferent pathway to the relevant effector organ. So pretty straightforward there, now it gets a bit more complicated when we are responding to emotionally salient or threatening or stressful stimuli because more brain regions are now going to be involved. So if we are, for example, encountering a threatening um stimulus, what's going to happen is some activation in our limbic system. So our amygdala is going to be processing that fear, that threat. We're going to be using our um our hippocampus to kind of think back into a long term memory. You know, have we encountered this before? How did we feel about it? How did we deal with it? And we are going to be consciously processing all of that in our prefrontal cortex? You know, thinking through how my feeling, why do I feel that way? How can I, you know, get through the situation and that information will get sent to our hypothalamus, which will decide if we're going to be turning on fight or flight or not. Basically. And then from there, the pathway is very similar. So the hypothalamus will send commands to the brain stem to the reticular formation, which will then send commands to the spinal cord. And then that nerve impulse will travel along the efferent pathway to the relevant organ now, you see, we also have this bidirectional arrow going back up from the hypothalamus to the limbic system and cerebral cortex. And that is there because sometimes when you know, let's say, for example, you're beginning to feel some fear and then your fight or flight response kicks in and you start to have that pounding heart, the increased respiration and well, your body has learned to associate that physical sensation with the emotion of fear. And so when you start feeling that physical sensation, it can actually increase your cognitions about fear and it kind of creates like a feedback loop. It doesn't always happen that way, but it can, so that's why that arrow is there as well. And you can see how in both of these um these pathways, the hypothalamus is still the structure that is in charge and, and, and is ultimately going to be sending out the commands for what the A NS should be doing. All right. So those are the levels of control in our A Ns and I will see you guys in our next video. Bye bye.

Control of the ANS Example 2

OK. So this one asks us, the blank acts as an integration center between areas of the brain that govern emotion and regions of the brain that control visceral functions. So remember when we're thinking about our autonomic nervous system, the region of the brain that is really the most important and is absolutely central to our processes is going to be the hypothalamus, which does indeed act as a relay station between those kind of higher level areas of the brain like our limbic system and cerebral cortex and the lower level areas like our brains stem that have a more direct influence on our visceral activity and homeostatic regulation. So our answer here is going to be c hypothalamus looking quickly at these other ones, the hippocampus is more involved in memory. Um Both memory formation and long term memory storage not really involved here at all. The reticular formation is one of those regions of the brain that does control visceral functions. It has a very direct impact on them, in fact, um but it's not involved as kind of an integration center. It's kind of just directly impacting those visceral activities and our limbic system is of course, involved in governing emotions, it involves our Amygdala. And so that's going to be one of those kind of higher level brain regions that helps us appraise emotions in the first place. So for example, if I was to, you know, walk outside and I saw a snake and I was to immediately appraise that as very threatening, maybe my, you know, my Amygdala immediately helps me feel some fear. I may start having some cognitions in my cerebral cortex. About, you know, is this snake venomous? How can I tell, how can I exit this environment and all of those cognitions and emotions are going to get sent to that hypothalamus which will process them and then send signals down to my brain stem and reticular formation to say, hey, you know, we have to activate that sympathetic division gear this girl up for some fight or flight, probably flight because I'm not going to fight a snake, right? And you know, get me out of that environment as quickly as possible. So that, that, that's kind of how that process would work. All right. So our answer here is c hypothalamus.

Which of the following brain regions is NOT involved in maintaining routine, homeostatic activity? 

• A. The hypothalamus.
• B. The reticular formation.
• C. The brainstem.
• D. The prefrontal cortex.