If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:8:23

Video transcript

why do we shiver when it's cold what did the Fivefinger say to the face in this video we'll talk about how our body uses our muscles to maintain a core body temperature that process is called thermal regulation the regulation of body temperature so in order to do that I'll first give you guys an overview of how thermal regulation works next we'll talk about how our bodies respond to hot temperatures before finally talking about how our bodies respond to cold temperatures so first if we have this gentleman right here who doesn't look very impressed and he's holding his hand up one day and notices it's really hot outside that looks really hot so the skin on his hand in his arm the rest of his body will perceive that it's really warm and in doing so this will create a neuronal signal a signal that's sent across neurons up into the brain and the part of the brain that perceives that it's really warm outside has a specific name it's called the hypothalamus the hypothalamus and in fact we split up the hypothalamus into two different parts to respond to two different types of temperature there's the anterior hypothalamus which just means the front of the hypothalamus and then there's also the posterior hypothalamus and that's just the back of the hypothalamus but which one responds to what kind of temperature well the way I remember it is that if it's hot outside we like to use the front of our hypothalamus or the anterior part of our hypothalamus to respond to temperatures that make it feel like we're on fire so if we're on fire we're going to use the front of our hypothalamus to respond well what if it's cold in those situations will use the posterior part or the back of our hypothalamus to respond to climates that make us say BRR we say BRR because it's really cold outside so we use the back of our hypothalamus okay so that all sounds good but what happens after our brain knows that it's really hot outside well then it sends back a signal - our body's telling it to respond to maintain our core body temperature and of all things to take point from here and act it's going to be muscles in our body that will do something to make sure we can maintain our core body temperature that will involve smooth muscle and when it's cold we also use skeletal muscle to respond to changing temperature so how does that work let's take a look when we're in a hot or a cold environment how to muscle help us respond here well the way to talk about this is to go through the two main types of muscle that will act here first there's smooth muscle specifically it's smooth muscle that lines our arterioles now arterioles are just smaller versions of our arteries arterioles the other type of muscle that functions here is called skeletal muscle and that's the type of muscle that works in your biceps your triceps all right now let's answer this question here why do you think arterioles have anything to do with temperature I mean how does that change whether we have a lot of heat in our body or not well the way that works is that if you take a look at a blood vessel I'll just draw a small one right here it's got a bunch of red blood cells and white blood cells and proteins and whatnot all of this is just kind of running around through the blood stream and the way it does that is just kind of in a random sort of motion or manner it's never directly forward but it just kind of bumps around like that and moves this way so overall you've got a general movement in the forward direction but you kind of are bumping around to do this and the interesting thing is this movement here this momentum that your red blood cells white blood cells or whatever you have in your bloodstream make that's energy so we have a ton of energy in our blood stream and energy is just another form of heat so if we are in a hot environment we want to get rid of this heat so we're going to put more heat to our most superficial or the most external parts of our body our skin so the more blood flow we get to our skin the more heat we can have leave our bodies and that's how we get to regulate our temperature so let's talk about it here when it's hot our smooth muscle then is going to relax and in doing so the arterioles then are going to become wider or larger and this process is called vasodilation your arterioles are dilating they're becoming wider and so the way you could see that happen is that this blood vessel that was about be a big is now going to become that big in the skin and so that means that you're going to have a lot more blood flow going in here to the skin you're going to have tons of red and white blood vessels and protein just kind of merrily tumbling about going like this that means you're going to have a ton more heat or energy that's present here that can then dissipate and leave and so that helps you cool off you're losing all of this energy or this heat that you have by diverting blood flow to your skin now what does skeletal muscle do here they don't do anything when it's hot they'll respond in a second and we'll talk about that when it gets cold what do smooth muscle do when we're in the cold well you can imagine that if we relaxed when it was hot it's fair to think that we're going to contract when it's cold and so this process then in the arterioles is going to be called vasoconstriction vasoconstriction which just means the narrowing of our arterioles and so if I were to draw that on a diagram right here you would see that this blood vessel that looked like this in our normal state is now going to turn into something more like that kind of a pipsqueak really tiny so you're going to have red blood cells white blood cells and protein just kind of shifting through here like this but there's not a lot of opportunity to kind of tumble around and be naughty they just got to go forward they can only go in one direction because there's not a lot of space here for blood flow and so in the skin you're going to have less energy or less heat that's present at this very external or superficial part of your body the more blood that you have that gets away from the skin the more that's going to go towards your core your core will then have more energy or more heat to help you stay warm when it's cold outside so that's what your smooth muscle does what do skeletal muscle do well skeletal muscle will also contract when it's cold but there's a very different purpose for why that happens when skeletal muscle contracts it's going to take ATP or adenosine tri or three phosphate and break that to make adenosine diphosphate ADP so that's two phosphates and we just snapped off a little phosphate group I'll write an AI here to show that it just snapped off but these aren't the only two things that are made you actually will produce energy as well and we call this reaction an exothermic reaction EXO meaning exiting or the leaving of thermal or thermic meaning heat or energy and so we're actually producing energy here by contracting our skeletal muscle this happens in our core muscle groups that cause more of the heat that's being produced from this reaction to be stored there to help us respond to these cold environments now this isn't such an unusual process that's so foreign to us the contraction of our core skeletal muscle groups is actually just called shivering this is the whole reason why we shiver when it's cold because we need to produce some energy by breaking off some phosphate from this ATP and that shivering then will help us warm up when we're in the cold and that's how our muscles help us respond to the temperature change