G’day team

-Apologies for the erroneous 'steemit' tag-
A few days ago I read an interesting new piece of research about the epigenetic changes that occur in muscle tissue when we work out. I was really excited to write a good article covering what these scientists had discovered, but as I got going I soon realised that without a basic understanding of what we know about muscles, there was just no way anyone would understand this research. So instead I’ve decided to write a series on the topic. I’ll be covering the following over the next week or so…

• Types of Muscles
• How Muscles Work
• How Muscles Grow
• Epigenetic Regulation in Muscle Growth

If I think of any other cool topics, of anyone has any questions or concepts they’d also like me to cover, I’ll write on those too. So let’s get started…

Types of Muscle

Let’s start with the real basics. The human body has three main types of muscle, each of which is customised for a specific role.

Skeletal Muscle

These are the muscles which allow us to move, walk and talk. They’re called skeletal muscles because they’re built around our skeleton, attaching to different bones at each end and contracting to cause movement across joints. Our skeletal muscles are the largest single component of our body weight, making up 40% of our mass, and their contractions also produce about 85% of our body heat.

Skeletal muscle has a few interesting features that we can look at too. They’re multinucleated, meaning that unlike most of the cells in our body which have one nucleus containing DNA, skeletal muscle cells have many. This means they have many copies of our genetic blueprint which they use for making important proteins, such as actin and myosin, to help muscle growth (more on this next post).

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Skeletal muscles are also what we call striated, meaning lined. These lines appear in skeletal muscle because the contractile units in each muscle (known as sarcomeres) are all arranged in an orderly fashion. More on this later, but ultimately this increases the contractile potential of skeletal muscle, making it potentially incredibly strong.

Finally, we should note one more simple thing about skeletal muscle. Skeletal muscle is generally voluntary, meaning that we are able to control its movements. But this doesn’t mean we’re always in control of its movements, as we’ll learn later most of our muscular contractions are controlled by involuntary parts of our brain which do things like maintain our posture and balance

Cardiac Muscle

This one, at least, is pretty self-explanatory. Cardiac muscle is specifically designed to do what no other muscle in the body can. To contract over and over again, for decades, and neither tire nor wear down. Of course, this process isn’t perfect, but our cardiac muscle does a great job of keeping our blood flowing for a long time. Now just like skeletal muscle, cardiac muscle is striated, with regularly arranged sarcomeres. But it’s here that the similarities finish.

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Cardiac muscle is mononucleotide, with a single nucleus per cell. It is also branched, meaning that each muscle cell has several projections which reach out like tentacles and intertwine with surrounding muscle cells. This feature means cardiac muscle is extremely strong, making it capable of withstanding the massive pressures created when our heart contracts and pumps blood all the way around our body.

Finally, as well all know, cardiac muscle is not voluntary, we cannot control our heart the same way we control our hand. Our heart’s contractions respond to parts of our endocrine (hormone) and nervous (neural) system that are not under our control, such as the release of adrenalin or stimulation by the vagus nerve.

Smooth Muscle

Smooth muscle is an incredibly important and often overlooked component of our everyday bodily functions. Unlike skeletal and cardiac muscle, smooth muscle doesn’t have any cool traits. Its non-striated, mononucleated, non-branched and ultimately very boring. But it’s in charge of a massive number of important physiological functions.

Smooth muscle wraps our entire digestive tract, from the esophagus at the back of our throat, all the way to our anus. Contraction of this smooth muscle can move food along our digestive system via peristalsis, churn it in our stomach, or halt its movement by contraction of strategically placed sphincters.

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Smooth muscle is contained in our eyes and allows us to control how much light enters to hit our retina, it wraps our arteries and veins allowing our body to control where blood flows and it makes up the uterus which squeezes each of us into the world. There’s a lot more that smooth muscle does, and if you’d like an awesome rundown I really advise you have a look at the wikipedia page or check out this open textbook. Smooth muscle, in my mind, is really the unsung hero of physiology.

*As we can clearly see, not all muscles are built the same. But as usual with science, the more we focus on one area, the more we realize that larger categories can be broken down into smaller sub-categories. So let’s talk about all the different classes of skeletal muscle and how they differ from each other.

Types of Skeletal Muscle

Now within this larger group of skeletal muscle, we have a few different sub-types too. Each one built for either strength or endurance. Most of the actual muscle-bundles in our body contain all three types of fibres but may have a heavy preference towards one or the other end of the spectrum.

Type I Muscle Fibers

These are what has been traditionally known as ‘slow twitch’ fibers. They’re not as quick to respond or even as strong as some of the other fiber types, but they’re masters at burning oxygen, meaning they can run for a long time. Think of a large car with a huge fuel tank, probably not super-fast over a quarter mile, but it’ll drive for days. Type I muscle fibers are also often classified as red-muscles because their good blood supply gives them a red appearance.

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Type IIa Muscle Fibers

These are sort of our intermediate fibers. They provide plenty of strength and speed, but they’ve also got the capacity to produce energy by utilizing oxygen. In our car analogy, they might be a nice grand tourer with a large tank but plenty of engine power to get off the mark. Type IIa muscle fibers are also quite well vascularized and considered red-muscle.

Type IIb Muscle Fibers

These are the drag-racers of the muscle world. With no capacity to burn oxygen these muscle reply purely on a process called ‘glycolysis’, which produces energy quickly, but also builds up plenty of nasty by-products. These muscles are super duper strong, but won’t work for very long when called upon. Because they don't rely on oxygen to work, type IIb muscle fibers don't have very good blood supplies, and are lighter in appearance, earning them the name white-muscle.

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On a fun side-note, some researchers have classified a group of ‘super-fast’ muscle fibers in the legs of 100m sprinters as type IIx. These fibers have also been reported in nature in the legs of super super-fast animals such as cheetahs. We should note, however, that this is not a mainstream scientific consensus, just a bit of fun research.
Awesome!

So they’re our types of muscle, next time we’ll have a look at just how muscles contract and how this relates to some of the physiological constraints we have when it comes to trying to lift things that are too heavy or workout for too long.

Thanks

As always, team, thanks for reading and I hope everyone learned something and had a good time! Stick around to check out my follow up posts too!

• All About Muscles - Part 2: How Muscles Work
• All About Muscles - Part 3: Muscle Growth

Thanks

-tfc

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