Control of the ANS - Online Tutor, Practice Problems & Exam Prep

The hypothalamus is the central command for the autonomic nervous system (ANS), regulating homeostasis through parasympathetic responses and reacting to stress via sympathetic pathways. It interacts with the brainstem, reticular formation, and limbic system, processing emotional stimuli and memories. The hypothalamus sends commands to the spinal cord, influencing heart rate, blood pressure, and digestion. This integration highlights the importance of the ANS in maintaining physiological balance and responding to environmental challenges, emphasizing the interconnectedness of brain structures in autonomic control.

Review of Relevant Brain Anatomy

Alright. So in this section, we're going to 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 going to 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 going to 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 up front, party in the back. Right? So I always think that a hypothalamus is sort of, like, calm, cool, collected up front. 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. Alright, next we have our brainstem which I'm sure you guys remember but that's going to act as kind of a relay center between our brain and our spinal cord and the rest of our body and it's going to contain some nuclei that help control autonomic functions. Alright, 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 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 our thalamus, hypothalamus, amygdala, hippocampus, among some others. And it's very important for the processing and interpretation of emotional stimuli. Right? So 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 cerebrum, we have our green brainstem, and you can see that blue reticular formation kind of running through the brainstem there. Oh, there we go. Alright, 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 options c and d because somatic and involuntary are not divisions of the autonomic nervous system. So we're left with options 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 upfront is calm, cool, collected. That's our parasympathetic division. And in the back, it handles all that stress. That is the sympathetic division. So if there was a lesion on the anterior, 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

Okay. So, let's dive into how those brain regions can work together to control our autonomic functions. As I mentioned, the hypothalamus is going to be the main integration center of the ANS. All of the commands are going to be coming from the hypothalamus. And as I kind of alluded to now, the ANS primarily operates in two ways. The first is maintaining homeostasis, and that, of course, is a largely parasympathetic response. It's also going to be responding to emotionally salient or stressful or threatening events, which is more of a sympathetic response. These two functions are going to involve slightly different neural pathways.

This first pathway where we're just maintaining homeostasis, we're going to have some kind of stimulus coming in. For example, the hormone levels in your blood, the chemical composition of your blood, the presence of food in your gut, something like that. The hypothalamus will process that and figure out what function we have to do to get back to homeostasis. For example, let’s slow down hormone production, let’s start digestion, whatever it may be. That command will get sent to the brainstem, 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. Pretty straightforward there.

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. If we are encountering a threatening stimulus, what's going to happen is some activation in our limbic system. Our amygdala is going to be processing that fear, that threat. We are going to be using our hippocampus to kind of think back into long-term memory. Have we encountered this before? How did we feel about it? How did we deal with it? And we’re going to be consciously processing all of that in our prefrontal cortex, thinking through how am I feeling? Why do I feel that way? How can I get through this situation? That information will get sent to our hypothalamus which will decide if we’re going to be turning on fight or flight or not. Then from there, the pathway is very similar. The hypothalamus will send commands to the brainstem, 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. That is there because sometimes when, 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. 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 pathways, the hypothalamus is still the structure that is in charge and is ultimately going to be sending out the commands for what the ANS should be doing.

Alright. So those are the levels of control in our ANS and I will see you guys in our next video. Bye bye.

Control of the ANS Example 2

Okay. 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 brain 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, 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, 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 the snake venomous? How can I tell? How can I exit this environment? And all of those cognitions and emotions are gonna 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 gonna fight a snake. Right? And, you know, get me out of that environment as quickly as possible. So that's kind of how that process would work. Alright. 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.

Here’s what students ask on this topic:

What role does the hypothalamus play in the autonomic nervous system (ANS)?

The hypothalamus is the central command center for the autonomic nervous system (ANS). It regulates homeostasis through parasympathetic responses and reacts to stress via sympathetic pathways. The anterior hypothalamus primarily directs parasympathetic activity, while the posterior hypothalamus directs sympathetic activity. It processes various stimuli, such as hormone levels and emotional stress, and sends commands to the brainstem, reticular formation, and spinal cord to influence heart rate, blood pressure, digestion, and other autonomic functions. This integration highlights the hypothalamus's crucial role in maintaining physiological balance and responding to environmental challenges.

How do the brainstem and reticular formation contribute to autonomic control?

The brainstem acts as a relay center between the brain, spinal cord, and the rest of the body, containing nuclei that help control autonomic functions. The reticular formation, a network of neurons and nuclei within the brainstem, regulates both skeletal and visceral muscle activity. It has the most direct influence on autonomic functions, becoming less active during parasympathetic activation. Together, the brainstem and reticular formation play essential roles in transmitting and modulating autonomic commands from the hypothalamus to the relevant effector organs, ensuring proper physiological responses.

What is the role of the limbic system in the autonomic nervous system?

The limbic system, which includes structures like the thalamus, hypothalamus, amygdala, and hippocampus, is crucial for processing and interpreting emotional stimuli. The amygdala processes emotions, while the hippocampus stores long-term and emotional memories. When encountering a stimulus, the limbic system helps recall associated memories and emotions, influencing the hypothalamus's decision to activate the sympathetic or parasympathetic response. This interaction highlights the limbic system's role in integrating emotional and physiological responses, contributing to the overall control of the autonomic nervous system.

How does the hypothalamus maintain homeostasis through the autonomic nervous system?

The hypothalamus maintains homeostasis by processing various stimuli, such as hormone levels, blood chemical composition, and the presence of food in the gut. It then determines the necessary actions to restore balance, such as slowing hormone production or initiating digestion. These commands are sent to the brainstem, reticular formation, and spinal cord, which relay the nerve impulses to the relevant effector organs. This pathway ensures that the body can maintain stable internal conditions, highlighting the hypothalamus's central role in homeostatic regulation through the autonomic nervous system.

What happens in the brain when responding to emotionally salient or stressful stimuli?

When responding to emotionally salient or stressful stimuli, the limbic system, particularly the amygdala and hippocampus, becomes active. The amygdala processes fear and threat, while the hippocampus recalls related memories. The prefrontal cortex consciously processes these emotions and thoughts. This information is sent to the hypothalamus, which decides whether to activate the fight-or-flight response. Commands are then relayed to the brainstem, reticular formation, and spinal cord, leading to physiological changes like increased heart rate and respiration. This process illustrates the complex interaction between emotional and physiological responses in the brain.