Your body contains over 600 named muscles. Some, like your gluteus maximus, are very big and powerful; others are tiny, such as the stapedius in your inner ear. Your muscles work in conjunction with tendons, ligaments and joints to produce movement and some muscles are also involved in the digestive process, breathing and circulation.
Types of Muscle
There are three types of muscle in the human body: smooth, cardiac and skeletal. Smooth muscle makes up hollow tube-like organs such are your blood vessels and digestive tract. Cardiac muscle is found in your heart and is responsible for pumping blood through your body. Skeletal muscle is attached to your bones via tendons and is responsible for movement and maintaining posture.
Muscle Functions
In addition to movement, muscles have many other functions. When you are cold, your muscles shiver to generate heat. This process is called involuntary thermogenisis. In emergency situations where food intake is severely limited, your muscles can be broken down for fuel. This process is called catabolism. Muscles provide protection from impact-related injury, acting like a football player's pads. Muscles help to dissipate impact over a large surface area and absorb shock to protect the underlying skeleton. Finally, muscles help push de-oxygenated blood back up your body against gravity, a process called venous return; thus, the blood can be re-oxygenated at the lungs.
How Muscles Work
Muscles are comprised of fibers which, in turn, are comprised of two types of protein filament; actin and myosin. Actin filament is thin, while myosin filament is thick. These two proteins combine in units called sarcomere, and each muscle is comprised of multiple bundles of sarcomere. When your nervous system stimulates, the actin and myosin filaments slide past each other to draw the ends of the muscle closer together. This results in tension within the muscles and movement of the joint that the muscle crosses.
Muscle Growth
Muscles respond to the stresses placed upon them. If you go to the gym and lift heavy weights, your muscles will respond, getting bigger and therefore stronger. This is a process called hypertrophy. Bodybuilders train specifically for muscular hypertrophy and use specially-designed workouts to achieve their well-developed physiques. If you don't stress your muscles with exercise, they will either remain the same size or will shrink, if you stop using them completely. This is called atrophy. Dramatic atrophy is often seen after a limb has been immobilized in plaster due to a broken bone.
Muscular Characteristsics
All muscles share a number of characteristics, irrespective of location or size. All muscles have a good blood supply and subsequently red, elastic and stretchable. Muscles are electrically excitable and contract when an electrical charge is applied to them. Muscles can generate tension as they shorten, called a concentric contraction; as they lengthen, this is called an eccentric contraction; while remaining the same length, this is an isometric contraction.
References
- "Atlas of Skeletal Muscles"; Robert J. Stone and Judith A. Stone"; 2008
- "Anatomy and Physiology for Dummies"; Donna Rae Siegfried; 2002
- "Principles of Anatomy and Physiology"; Gerard J. Tortora and Bryan H. Derrickson; 2008
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