The human muscular system is responsible for roughly one half of the body's weight. You may have heard someone complain about gaining weight with exercise instead of losing it. This occurs because the cells that make up individual muscles increase in size and weigh more than fat content.The increased cell size is what gives muscles their "toned" appearance. When these cells decrease in size it is known as atrophy.
The muscular system is designed to create force and cause motion which is why we often think of skeletal muscles when the muscular system is discussed. There are actually three distinctive types of muscle that make up the muscular system. Skeletal, smooth and cardiac. These are made to function in very different ways with their own unique purposes. All muscle action work in extend or contract movements to acquire what they are supposed to achieve..
Our bodies contain six hundred and fifty skeletal muscles. These muscles are attached to the skeleton giving them their name. All skeletal muscles work in pairs. One muscle will move the bone one way and the paired muscle moves it back. These are what are known as voluntary muscles. That means we must think about what muscle we want to move and they react.
There are ten groups of muscle that consist of skeletal muscles. These include facial, neck, shoulder, arm, forearm, thorax, hip, pelvis, thigh and leg. All skeleton muscles require tendons and ligaments to function correctly. When a tendon or ligament is torn or injured proper muscle function becomes impossible.
The smooth muscles are involuntary, meaning that they do not have to be given thought to work. The central nervous system is in control and causes them to contract accordingly. Smooth muscles are located in our internal organs. The digestive system, female uterus, respiratory organs, blood vessels and our bladder are all controlled by smooth muscles. They are also responsible for eye movement.
The cardiac muscle is what makes up the human heart. The cardiac is another example of an involuntary muscle. This muscle is controlled by the part of the brain known as medulla oblungata. The cardiac muscle continues to beat on its own without us having to concentrate on it. Cardiac muscle is thick and strong, which enable it to pump blood out of the heart, then relax to let it flow back in.
Images depicting the various muscles can be seen at The Human Body. Having a visual aid can make it easier to understand how the various skeletal muscles are placed throughout the human body.