The human body consists of roughly 700 individual muscles, comprising approximately 40 to 50 percent of an adult's total body weight. Muscles play a more pivotal role for humans than simply aesthetic purposes. In many ways, muscle contributes to the achievement and maintenance of homeostasis, a constant internal environment. Thanks in large part due to the scientific study of muscle, known as myology, we know that muscles have myriad responsibilities within the human body.
Function
Primary responsibilities of muscle in the body include contracting and relaxing to cause movement of the bones of the skeletal system. By its role in the conversion of chemical energy into mechanical energy, muscles generate force to perform work and produce movement. Other duties involve the stabilization of body position, generating heat and assisting in the propulsion of foods and fluids throughout varying systems of the body.
Types
There are three types of muscular tissue in the human body: skeletal, cardiac and smooth. Skeletal muscle is attached directly to bones. As its name implies, cardiac tissue is found only lining the heart wall. Internal organs are where smooth muscle tissue is located. Smooth and cardiac muscles are considered involuntary muscles. Their contractions occur without our conscious involvement. Skeletal muscle, on the other hand, is considered to be voluntary, as we are able to consciously contract and relax these muscles.
Properties
Muscle tissue possess four unique properties: electrical excitability, contractility, extensibility and elasticity. Electrical excitability means muscles can respond to a stimuli sent by the nervous system and produce what is known as an action potential, or electrical signals. Contractility refers to the contractile nature of muscle to produce tension in effort to perform work. Extensibility means muscles can be stretched, while elasticity suggests that after being stretched or contracted (shortened), muscle can return to its original shape.
Structure
Skeletal muscle is made up of three types of muscle fiber: slow-oxidative (SO) fibers, fast oxidative-glycolytic (FOG) fibers and fast glycolytic (FG) fibers. SO fibers are integral in performing aerobic endurance type activities. FOG fibers are a hybrid of the other types, possessing characteristics of both SO and FG. FG are engaged primarily during rapid, short bursts with high intensities. SO fibers, which are replete with mitochondria and capillaries, have a high resistance to fatigue. Endurance athletes tend to have a higher proportion of SO fibers. Conversely, FG fibers have a low resistance to fatigue. Track sprinters typically have a higher proportion of FG to SO fibers.
Imbalances
Homeostatic imbalances can cause abnormalities in skeletal muscle function. Fibromyalgia is a painful muscular disorder that affects approximately 3 million people in the United States. It is more common in women than in men. Symptoms include pain, tenderness and stiffness in muscles, tendons and surrounding tissue. Also associated with this condition are reports of severe fatigue, disrupted sleep, headaches and depression. Treatment includes the application of heat, gentle massage and medication for pain.
References
- "Principles of Anatomy and Physiology, 12th Edition;" Tortora, Gerard and Derrickson, Bryan; 2009
- "Introduction to Sports Medicine and Athletic Training;" France, Robert; 2004
