The human muscular system performs numerous useful functions, including keeping the heart contracting to body movement. Muscles relax, contract, lengthen and allow a variety of action.
Muscles in the Body
There are about 650 muscles in the body, and some believe this number can climb to as many as 850 muscles. There is not an exact figure because of the disagreement about what separates one muscle and where another muscle branches off.
Three Types Of Muscle Tissue
Cardiac, smooth and skeletal muscle are three types of muscle tissue. The function of cardiac muscle is the pumping of blood and is found in the heart. Cardiac muscle has an involuntary control where its speed of muscle contraction is moderate (0.15 seconds). Cardiac muscle has a low likelihood of fatigue because the heart relaxes between contractions. Smooth muscle is found in the walls of organs and within the walls of blood vessels where its functions include controlling blood vessel diameter and movement. Smooth muscle has a slow contraction speed of one to three seconds and usually does not fatigue. Attached to tendons that attach to bones is skeletal muscle, which is in charge of the maintenance of posture and movement of the body. Contracted at a speed of 0.05 seconds, the voluntary controlled muscles can fatigue depending on the type of work load.
Functions of Muscular System
Many functions of the human body are tied to the muscular system. Body posture, maintenance and movement is contributed to the contraction of your skeletal muscles. Moving liquids and solids within the digestive tract is taken with aid from smooth muscle tightening of vessels and organs. Blood is moved through your body with each heart beat because of the contraction of cardiac muscles within the heart. Body heat is produced as a byproduct of muscle contraction.
Various Muscle Sizes
Muscles vary in size. A muscle in the middle ear that is thinner than a thread is called the stapedius muscle. It is responsible for sending vibrations from the eardrum to the inner ear. The largest and one of the strongest muscles is the gluteus maximus muscle in the buttock. The gluteus maximus straightens out the hip joint and moves the thigh bone away from the body.
Naming Muscles
Descriptive names are given to skeletal muscles according to various features. The location of a skeletal muscle can be given a name such as pectoralis (chest) or brachii (arm). Looking at the name of origin and insertion of the muscle for example, brachioradialis lets you know this muscles origin is on the brachium (arm) and insertion on the radius bone. The shape of the muscle can be another determinate, such as the triangular deltoid muscle or the rhomboid muscle, which looks like a rhombus that has equal parallel sides. Also, muscles can be named for their action, direction of fibers, size or numbers of origins, such as the biceps, which has two heads.
References
- "Manual of Structural Kinesiology"; R. T. Floyd; 2006.
- "The Handy Anatomy Answer Book"; James Bobick and Naomi Balaban; 2008
- Medline Plus
