System Update: Muscles

Oh the muscular system. Curious isn't it? All these muscle fibers upon muscle fibers contain little tiny sarcomeres that expand and contract all at the same time. Millions of them working together to cause contraction. Not to mention how our muscles are attached to the bone in strategic places to move our body in what seems like an infinite number of ways. Each muscle is uniquely fitted designed for specific movements and placements. The anatomy of muscle is simply astounding. Lets take our shoulder muscles for example. Brachialis and Deltoid are two muscles that are responsible for working with about 10 other muscles to move the arm in its rotator cuff. When you move your arm around this "system" of muscles work together to produce the desired motion. 

http://www.ehs.utoronto.ca/services/Ergonomics/exercise.htm

Don't even get me started on the physiology... (just kidding this is for a grade so I kind of have to 'get started' on the physiology) Muscles are primarily for movement. That is their main function. How does this happen you ask? Well it all starts out with an Action Potential. An Action Potential in this case is an electrical impulse that causes the change throughout the muscle cell. When the action potential hits the membrane of a muscle cell, there is an activation of Sodium Potassium pumps. The normal diffusion is now affected and the sodium and potassium concentrations go askew causing a depolarization of the cell (the cell flipped charges now its negative on the inside). Because of this the Sarcoplasmic reticulum (The storage center for calcium) releases calcium around the muscle all at once. Then the calcium bonds to troponin and tropomyosin causing them to change shape (and ultimately function) of the protein. The tropomyosin is then changed so the active sites on the actin are now revealed.  I like to think of this as like a rock climber or batman. They have that cool hook thingy on a rope and they throw it on top of something  and propel up. Well I think of the myosin as the grappler thing and the active sites of actin as like the thing it hooks onto.  Here is where we get into the sliding filament theory. The two filaments actin and myosin slide past each other. It is the revealing of active sites that allow the filaments to connect or hook-on to each other and contract. I know long process it seems but, it happens over the course of a few milliseconds. 

Homeostasis in the muscular system works just like any other system. We have a stimulus and a response. A fantastic example to use is when our body is subject to extreme temperatures. 

http://apblogandrewstarck.blogspot.com/2010/09/homeostasis.html

The initial stimulus is the cold outside which starts cooling our overall body temperature.  Our body then decides that it needs to do something. So, it decides to start muscle contraction, which at the cost of ATP produces a byproduct of heat.  Muscles also help us voluntarily act for homeostatic balance. If put my finger in boiling water it burns and my muscles react by pulling my finger out of the water. 

Muscles, gotta love 'em