Muscle Tissue

Muscle Tissue Definition

Animals have muscle tissue which functions by contracting, thereby applying forces to various parts of the body. Fibers of muscle cells are connected in sheets and fibers to form muscle tissue. 

Combined, these sheets and fibers form muscles, which control an organism’s movements, as well as other contractile functions. An animal’s muscles can be classified into three types based on their purpose. Although they differ slightly, these muscles perform similar tasks.

Function of Muscle Tissue

Often, muscle tissue is connected to the same nerve bundles as a single unit. The muscle contracts when it receives a nerve impulse from the brain or another external signal. Muscle tissue contracts almost instantly as the nerve impulse passes through all the nerve cells.

Each muscle cell contains a complex of proteins containing actin and myosin. When the signal to contract is received, these proteins slide past one another. Filaments are attached to the ends of the cells, and as they slide past one another, the cells contract. 

The length of a single cell can be reduced by up to 70% during contraction, resulting in a shortening of the entire muscle. Bones can be moved by muscle tissue, chambers can be compressed, and organs can be squeezed by muscle tissue.

Types of Muscle Tissue

Skeletal Muscle Tissue

Skeletal muscle tissue is a type of striated muscle, meaning clear bands can be seen in it under a microscope. These tiny light and dark bands are sarcomeres, highly organized bundles of actin, myosin, and associated proteins. These organized bundles allow striated muscle to contract quickly and release quickly. 

Muscle tissue is attached to the bones through tendons, which are highly elastic portions of connective tissue. Many muscles may seem to control a single appendage, but in reality each one only controls one small aspect of movement. Skeletal muscle tissue can be controlled voluntarily, by the somatic nervous system. The other types of muscle are controlled mainly by the involuntary or autonomous nervous system.

Cardiac Muscle Tissue

While the striations in skeletal muscle tissue are even and parallel, complex and branching striations are seen in cardiac muscle tissue. While the striations are hard to see in this image, the branching nature of the cells is easy to pick out. 

The branching is caused by the connection of cardiac muscle cells to one another. The cells are connected via intercalated discs. These junctures help cardiac muscle to contract as one and provide a rapid and coordinated contraction to move blood.

Smooth Muscle Tissue

Unlike cardiac and skeletal muscle tissue, smooth muscle tissue has no striations. The fibers of myosin and actin in smooth muscle fiber is not nearly as organized as in the other types of muscle tissue. In smooth muscle, the contractions are not quick and rapid but rather smooth and continuous. 

Smooth muscle is found surrounding many organs, blood vessels, and other vessels used for transporting fluids. The smooth muscle can contract to apply a force on organ.

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