on action potential will cause muscle fibers to twitch, as it's called, so a single action potential results in a single twitch. Now the tension, the difference intention that you can create in your muscle is due to action potential frequency. So the higher the frequency of the action potentials, the more tense the muscle will become. And this can actually lead to something known as tetanus, which is sustained muscle contraction because the twitches fuse together. Now you can see a model of that happening here where we have an action potential, this red spike. And then here in blue, we have the twitch of the muscle, and here you can see the frequency of action potentials. Each one of these lines is an action potential coming in, and here you can see the resulting tension, how the frequency of the action potentials is actually going to cause the tension to increase. Now there's actually different types of fibers designed for different types of twitches. There are what we call fast twitch fibers that contract very rapidly and slow twitch fibers that contract slowly. Now. The reason you want both of these is they serve different purposes. Those fast twitch fibers contract very quickly, but they'll tire out quickly as well. And this is in part because they rely on, uh, a teepee from like Allah assists instead of aerobic respiration, which is going to allow them to get a lot of ATP really quickly. But it's not going to be as sustainable because aerobic respiration provides a much higher yield of ATP. Now these slow twitch fibers can sustain longer contractions. They're not gonna tire out as quickly. And they are going to contract mawr slowly due to a, uh, the rate of 80 p hydrology sis in mice. And that's what's actually going to control that, or what's going to cause it to actually slow down. Now muscles contain a special oxygen binding protein called myoglobin, like hemoglobin, for example. You know, similar similar idea there, of course, it's, um, gonna be a bit different from hemoglobin. However, it's an oxygen binding protein, Um, and its purpose is to actually store oxygen so that when the oxygen demand and muscles is very high, and perhaps that hemoglobin can't provide everything they need, we have this store in myoglobin. Now there are different types of muscles, and they could be grouped based on whether they're controlled by conscious thought or unconscious signals. So voluntary muscles, which are controlled by conscious thought our, uh, skeletal muscles and these air going to be those strident muscles made of long my A fib. RL now, involuntary muscles are, as we said, controlled by unconscious signals and thes. They're gonna be regulated by a division of the nervous system known as the autonomic nervous system. Now they're gonna be two types of involuntary muscles smooth muscle, which actually doesn't contain my A fib, rials. And these are going to line blood vessels, the digestive tract, and they're going to be responsible for parastatal sis. So these air actually a very important type of muscle, Um, just made of, you know, little individual cells that will contract in, you know, a different way than these my A fib roles. They'll still use those acting in mice and interactions, but they're not gonna have these long chains of SAARC. Amir's that are, um, you know, going to chain together those contractions now, cardiac muscle is striated, and it, uh, contained you know, it's dry it So it contains Sark Amir's. However, it is on involuntary muscle. You don't have conscious control over your heart rate. Um, and it's gonna have this special feature known as inter kill ated discs. Thes are basically like, uh, they're gonna have gap junctions. More or less. There's a little more to them, but they involve gap junctions, which are those direct connections between cells. And that's gonna allow action potentials to spread through the cardiac muscle. And this is gonna be very important for heart contraction, which relies on the spread of these action potentials flowing through the heart. Thio create the rhythmic heartbeat. Now with that, let's go ahead and flip the page.
