Muscular Tissue – Structure and Types
It constitutes the muscles, made up of myocytes, (muscle cells) which are in the form of contractile fibres varying in lengths.
Muscular tissue in general develops from the mesoderm of the embryo but the muscles of the iris of the eye and myoepithelial cells of the salivary, mammary and sweat glands arise form the ectoderm of the embryo.
Muscle tissue definition:
The special property of muscular tissue is contractility i.e., the cells of muscular tissue can shorten considerably and return to the original relaxed state. The muscle cells contract in a definite direction.
Another property of muscle is the electrical excitability. It is due to the energy stored in the electrical potential difference across the plasma membrane.
Structure of muscular Tissue
About 85% of the mass of a muscle is made up of muscle fibres; the remaining 15% is mostly connective tissue. Muscle is organized and largely shaped by the connective tissue, which is composed of a ground substance, collagen, and recticular and elastin fibers of varying proportions.
In muscle, the connective tissue is largely responsible for transmitting forces, for example the transmission of forces from the muscle to the bone by the tendon.
The connective tissues’ elasticity and distensibility help to ensure that the tension developed by the muscle is smoothly transmitted and that a muscle will return to its original shape after being stretched. Thus, the connective tissue of a muscle provides a framework for the concept of series and parallel elastic components within a muscle
There are three levels of muscle tissue organization : epimysium, endomysium, and perimysium. These three levels are a consequence of differing sizes and orientations of connective tissue fibers, particularly
The outside surface of a muscle is covered by a relatively thick and very tough connective tissue, the epimysium, which separates it from surrounding muscles. Arteries and veins run through the endomysium. The collagen fibers of the epimysium are woven into particularly tight bundles that are wavy in appearance. These collagen bundles are connected to the perimysium. The perimysium divides the muscle into bundles typically containing about 100 to 150 muscle fibres,
which form a fasciculus or fascicle.
The perimysium contains many large collagen bundles that encircle the outer surface of the muscle fibres lying on the outside of a fascicle.
Underneath the thicker perimysial sheets of connective tissue is a much looser network of collagen fibers that run in various directions and connect with the endomysium.
The endomysium, which is made up of collagen fibers 60 to 120 nm in diameter, surrounds each muscle fiber, again adding more stability.
What are the functions of muscle tissue
Functionally, smooth muscle fibres can be of two types:
–– Single unit smooth muscular tissue: Muscle fibres are closely joined together and contract as a single unit. They are found in walls of hollow visceral organs.
–– Multi unit smooth muscular tissue : Muscle fibres contract as separate units. They are found in the wall of large blood vessels, arrector pili muscles of skin dermis, ciliary and iris muscles in the eyes.
Furthermore, cardiac muscular tissue is the one which helps in the heart beat.