Muscles control movement and internal organs.
Muscle cells allow the bodies of animals to move and control internal organs, such as the kidneys and intestines. Within each muscle cell are muscle fibrils that are key to muscle contraction, which in turn are covered with endomysium, a connective tissue that surrounds the whole muscle. All together, these cells and tissues make up our muscular system.
Types of muscle
Muscle can be separated into three subcategories. Skeletal muscle has a series of ridges or linear marks called striations along the surface. These muscles are under voluntary control and are used primarily in movement. Smooth muscle makes up hollow organs, such as the kidneys. And cardiac muscle is present in the heart and has some of the striations in skeletal muscle.
Lifespan
Some smooth muscle cells only have a lifespan of a few days. However, skeletal and cardiac muscle remains unchanged once created. Therefore, their cells have the potential to live as long as the body in which they function.
Differences
Muscle cells differ from other cells in that they consist of much more protein, specifically actin and myosin proteins. Unlike other types of cells, these proteins work together to shorten the muscle and, hence, move.
Skeletal muscle cells are also special in that they can have more than one nucleus (the powerhouse of a cell), whereas most cells only have one.
All muscle fiber is developed while in the womb, so rather than creating new muscle when taking part in physical training, you are actually making pre-existing muscle tissue bigger and stronger.
Creation
Muscle cells are formed from stem cells during the growth of an embryo and fetus. Stem cells are cells that have the ability to develop into a large array of other types of cell. The creation of muscle is called myogenesis.
Myogenesis comes in two phases. The first is the creation of primary fibers, which happens during the very early stages of embryonic life. These fibers are then distributed throughout the muscle-forming parts of the body.
The second phase of myogenesis involves the generation of secondary fibers. This happens during the fetal stage. Many of the smaller secondary cells grow on top of each primary cell, using the primary cells as a kind of scaffolding. Therefore, there are many more secondary cells than primary.
Toward the end of the fetal stage of development, adult myogenic cells are created and then remain after birth. These myogenic cells are responsible for the regeneration and creation of muscle during the life of the organism.
Death
A cell’s death can fall into two categories: necrosis, which is death caused by injury or disease that cuts the cell’s natural life short, and apoptosis, which is the natural or programmed death of a cell caused by the cell exceeding its lifespan or by the cell not working properly.
Within muscle cells, necrosis is characterized by the swelling of the cell or the disruption of its components. Apoptosis of muscle cells, on the other hand, is characterized by cell shrinkage. The remains of the cell are then phagocytized (engulfed and dissolved) by adjacent cells.
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