Skeletal Muscle Contraction

By: JT Lenga



Hello readers! This week, I decided to share with you the process of how our muscles contract. This is yet another thing I have learned in my Foundations of Kinesiology class taught by Dr. Pontifax. I will try to keep it simple for those of you not familiar with anatomy/ physiology. 
In order to know how contraction takes place, we need to know the structure of our muscles. Our muscles are made up of three major parts. First, is the entire muscle; second, is the muscle fascicles; and the final, is the individual muscle fibers. The muscle contains the fascicles and the fibers. Within the fascicles, are bundles of individual muscle fibers. 

The muscle fibers are the muscle cells. These cells are multi-nucleated (more than one nucleus). Muscle cells are composed of a sarcolemma (the membrane of the muscle fibers), sarcoplasm (cytoplasm of a muscle), sarcoplasmic reticulum, the transverse tubules, and the myofibrils. 

The sarcoplasmic reticulum releases calcium ions during muscular contraction, and it will also reabsorb the calcium ions during relaxation. Transverse tubules are located perpendicular to the myofibrils. They are the major sites for excitation and contraction.

Myofibrils are the basic unit of a muscle. Within the myofibrils are contractile proteins organized into thin and thick filaments. These filaments are called actin (thin) and myosin (thick). Actin provides binding sites for myosin, and the myosin have fibrous tails with globular heads that will bind to the actin and pull the actin filaments together. 

Now that we have the basic structure, we can discuss how our brain tells our body to move.

In order to have contraction, we need three things: an action potential (brain signal), calcium ions, and ATP (energy). First an action potential is sent to the muscle and is transferred along the sarcolemma. next the action potential activates calcium channels in the transverse tubules which will then let the calcium flow into the cell and activate calcium channels in the sarcoplasmic reticulum. The calcium ions from those channels then bind on to something called troponin. Troponin is like a lock on the actin, basically it utilizes tropomyosin (blocking mechanism) to block the myosin heads from binding to actin. Once the calcium binds to troponin, tropomyosin is moved from the binding sites allowing myosin heads to bind and pull on the actin. ATP come in to then release the myosin heads from the binding sites. Once the muscle goes to relax, the ATP and calcium ions are reabsorbed. 

Below is a video that shows the process of contraction. 

Muscular contraction is something that literally moves the kinesiology field. Like all systems of the body it is something that I feel that people should have at least a basic understanding of. If people knew how their own bodies worked I think that the information could help a lot of people avoid some of the most common health problems that most people face today. You only have one body if you don't know how to use it and it breaks there is no return policy. 

References 

"Cite A Website - Cite This For Me". Upload.Wikimedia.Org, 2017,       https://upload.wikimedia.org/wikipedia/commons/9/94/1023_T-tubule.jpg.

"Cite A Website - Cite This For Me". Upload.Wikimedia.Org, 2017, https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/1007_Muscle_Fibes_(large).jpg/300px-1007_Muscle_Fibes_(large).jpg.

"Muscle Contraction - Cross Bridge Cycle, Animation.". Youtube, 2016, https://www.youtube.com/watch?v=BVcgO4p88AA.

Pontifax, Matthew. "MSU - KIN173 - Foundations Of Kinesiology - Spring 2017". Education.Msu.Edu, 2016, http://education.msu.edu/kin/courses/kin173/#CSCHEDULE.