The Contractile Muscle!

Muscle contraction, it is required for almost anything you carry out. Right from driving the car to reading this article, muscle contraction is required for a plethora of things. There are around 600 muscles in the body. As a matter of fact, it accounts for up to 85 percent of the heat produced in the body. So, without muscle contraction you would probably die of hypothermia. Aside from all these beautiful facts, have you ever thought about how muscles contract?

Well, if you have not, do not worry! by the end of this article, you would be an expert!

Just to make things clear, I will be discussing the mechanism for the contraction of skeletal muscles (which are the voluntary muscles in the body). So, let us get to the crux of it!

Before getting to the interesting part, I would have to brief you up on some aspects of muscle anatomy. A muscle has many components to it. Each muscle is made up of muscle fibers and a group of fibers are called a fascicle and many fascicles make up a muscle. One fiber is surrounded by a tissue called endomysium, one fascicle is covered in another tissue called perimysium and finally, one muscle is covered in epimysium.

Now to the interesting part, muscle fibers are made of two proteins called actin and myosin. These are the proteins that aid in contraction of muscles. Myosin contains heads, these heads bind to actin, which is what causes the muscles to contract. However, it is not as easy as you think! Actin is covered in a layer of protein called tropomyosin. Tropomyosin is what prevents the myosin head from binding to actin. To add to the complexity, there is another protein. Yes! Another protein! This protein is called troponin. This very protein helps bind the tropomyosin to actin. Furthermore, there are three types of troponin: troponin ‘I” – which binds to actin, troponin ‘T’ – which binds to tropomyosin and troponin ‘C’ – which binds to calcium ions. So, for the muscle to contract, the tropomyosin layer should be disintegrated. Let us see how!

When an impulse reaches the muscle(if you want to know more about this impulse, ;click here), it is carried through T-tubules in the muscle, which are invaginations of the muscular membrane. As the impulse is carried in the muscle, it causes calcium ions to enter. These calcium ions bind to troponin C, which if you remember is the protein that binds to calcium. This binding causes the tropomyosin to move away from the troponin and hence allowing the myosin heads to bind to actin. After myosin binds, it forms a link with actin. This link creates a ‘stroke’ between myosin and actin. This stroke is what causes the muscles to contract.

What about muscle relaxation/slackening? Well, for that to occur, ATP (adenosine triphosphate) binds with myosin causing it to unbind(uncouple) from actin and ultimately causing the muscle to react.

You are now officially an expert in muscle contract! There are several things going on just to carry out a small contraction of a muscle. It is needed for almost anything you can think off. I do not think there is anything that does not require a muscle. Imagine living without muscles, you could not even talk! Be grateful to your muscles! You owe them a lot!