The muscular system parts refer to the types, locations and the number of muscular The organs in the human body, as you can see in the muscular system diagram. According to the most recent research findings related to the human anatomy, there are more than 700 types of contractile organs in the body that have been identified and given particular names by the scientists. However, to make the study more comprehensive and understandable, all of these contractile organs have been grouped in three major categories, namely, skeletal muscles, smooth muscles and cardiac muscles. A brief description of these three major groups of human muscular system is being given as under:

Skeletal Muscles

These are considered as a form of striated muscles that are set into operation and controlled by the somatic nervous system. In other words, these are subjected to movement or resisted against a move with an individual's own will and, that is why, you can call them voluntary contractile organs. Concerning their location, as the very name suggests, these muscles are associated with the bony skeleton and are firmly attached with the bones through collagen fibers or tendons.

The individual components that combine to form these larger structures are known with three different names, viz. muscle fibers, muscle cells or, simply, myocytes. These unitary structures are formed in the process of myogenesis during which the developmental myoblasts undergo fusion to form larger multinucleated cells. These longer, cylindrical, larger and multinucleated structures are, in fact, termed as myocytes or myofibers. Concerning "What is a myoblast"; this is a kind of embryonic progenitor cell that develops to form a muscle cell.

The myofibers are, in turn, made up of myofibrils which contain actin and myosin filaments. The repetition of these actin and myosin fibers results in a structure, called sarcomere. Sarcomere is not only considered as the basic functional unit of the muscle fiber, but it also accounts for the striated appearance of the contractile organ. In other words, it forms the basic machinery that is needed for the mechanism of muscle contraction.

Cardiac Muscles

Like skeletal muscles, the cardiac or heart muscles are also striated, but unlike the former, the latter are involuntary and do not come under the voluntary control of an individual. Unlike the skeletal muscles, here you will find only one unique nucleus in each cell but the process of their formation is the same, i.e. myogenesis. These contractile organs contribute to the synthesis and development of the walls and histological components of the heart, including the myocardium.

The cardiac muscle cells contract in coordination with the nearby cells and as a result, the blood is propelled out of the atria and ventricles. These vital heart muscles are ensured ample supply of blood through the coronary arteries. By means of this circulatory fluid, the muscle cells not only get replenished with oxygen, but are also able to remove the waste products, such as carbon dioxide (CO2).

Smooth Muscles

As opposed to the other two major types of muscles, these are not only involuntary in action but also non-striated in appearance. These contractile tissues are divided into two types, i.e. single unit or unitary smooth muscle tissues and multiunit smooth muscle tissues. Talking about their location, the smooth muscle tissues are scattered across many parts of the body, such as blood vessels (including arteries and veins), lymphatic vessels, uterus, urinary bladder, respiratory tract, male and female reproductive tracts, gastrointestinal tract, the ciliary muscles, iris of the eye and arrector pili of the skin.

The smooth muscle cells located in different organs of the body show structural and functional similarities, but there is a substantial difference in the nature of inducing stimuli. This significant difference in the inducing stimuli is very necessary, so that individual desired effects are performed in the body at individual times. The contraction of a smooth muscle is caused by its excitation which is, in turn, induced by external stimuli. When the filaments of actin and myosin slide across each other, the result is the contraction of smooth muscles. Contraction is followed by the relaxation, thus initiating a rhythmic impulse across the length of the vessel or tract.