Skeletal Muscle!

Diagram showing all the -mysiums and the fascicle

Skeletal Muscle is awesome! It allows us to run, smile, and give high fives. It's composed to hundreds to thousands of muscle cells, connective tissue wrappings, and blood vessels and nerves. Each cell spans the length of the muscle! Take the Sartorius, a very long muscle in the thigh region. This muscle can be a couple feet long, which is pretty crazy because most people thing of cells as tiny things. How does such a large cell survive, you ask? They are extremely skinny, perfectly suited to reside in our skeletal muscle. The cells are multinucleate and are thin enough for nutrients to get in and waste to be excreted. The cells are in bundles called Fascicles. In between the cells, also called fibers is the Endomysium. Perimysium surrounds the bundles, and Epimysium holds it all together on the outer surface. These three layers are essential in skeletal muscle; this type of muscle goes through a lot, pulling on the bone all the time. The reinforcement keeps the muscle from tearing, and possibly tearing off the bone if enough force is applied.

Arnold doesn't know how much
effort it takes his body to flex! 

The main goals of the muscular system include movement, heat generation, stabilizing joints, and maintaining posture. None of these would be possible without contraction. Did you know only one third of our muscle cells contract at any one time? If they all contracted, it would be too much force to handle and the muscle could rip from the bone!  The smallest unit of contraction in skeletal muscle is the sarcomere. In the sarcomere are the two proteins that facilitate contraction, called myofilaments. The myofilaments are called Myosin (thick filaments) and Actin (thin filaments). During contraction, the Actin slides towards the center of the sarcomere, pulling the edges of sarcomere (Z Plate) and shortening the cell. When all the cells contract together, movement is produced! Since we know that skeletal muscle is voluntary, you tell your arms, legs, and hands to move to perform a certain function. This seems like a long process, here's how it goes. You decide you want to raise you arm, so your brain sends an electrical signal to the muscle. This signal starts a chain of chemical reaction and uses some ATP to attach the Myosin and Actin. The Actin slides, and your arm moves. Then more ATP is used to relax your arm. This whole process took longer to read than it took to actually happen! This long, specific series of impulses and reactions took place without much though in a fraction of a second! Pretty amazing if you ask me!


Diagram image from http://people.eku.edu/ritchisong/301notes3.htm
Arnold image from http://www.maloneyperformance.com/Blog/?p=390