The cells that make up muscle tissue are elongated and, for this reason, are also called muscle fibers.
Be careful not to confuse the term muscle fibers, which are cells, with connective tissue fibers, which are not cells but formed solely by the association of several macromolecules.
There are three types of muscle tissues, each composed of muscle fibers with their own morphological and functional characteristics. The distribution of each type in the body is also unique for each type.
All muscle fibers have in common:
– the presence of a large amount of contractile proteins, primarily myosin and actin. The way these proteins are organized differs among the three types of muscle tissue.
– the ability to generate movement or tension as a result of contraction of the muscle cells.
As these cells are elongated, they can undergo significant longitudinal shortening, generating movement. When the cells contract without shortening, they generate tension.
Due to the peculiar organization of contractile proteins in two types of muscle fibers, these are called striated muscle tissue. Why? When viewed under a microscope, their fibers exhibit transverse bands along the cytoplasm.
In the third type of muscle fiber, the arrangement of contractile proteins is quite different, and the cells do not have transverse striations. This type is called smooth muscle tissue.
Main features of muscle tissue cells:
– Skeletal striated muscle – has voluntary contraction, it constitutes the body’s musculature attached to the bones, as well as muscles not attached to bones, such as muscles located in the skin (mimic muscles), the orbicularis oculi, and some others.
– Cardiac striated muscle tissue – have involuntary contraction, they constitue muscle the heart – the myocardium – and is also found in the initial portion of the aorta.
– Smooth muscle tissue – has involuntary contraction, it constitutes the musculature of the viscera and of the walls of blood vessel .