concept muscle

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14th November, 2015
Anatomical and Functional Features of Skeletal Muscle
The smallest unit of contraction of skeletal muscle is called a muscle fiber. Various muscle fibers assemble to form muscle fasciculus. There are various connective tissues that cover these muscle parts. Each muscle fiber is enclosed in a connective tissue sheath called endomysium. The entire fasciculus is similarly covered by perimysium. The Epimysium is collagenous which extends from tendons and covers the entire skeletal muscle. The skeletal muscle is innervated by nerves that carry action potential to the muscles for initiating muscle contraction.
Further, there are blood vessels in the skeletal muscles that supply them with oxygen ad necessary oxygen. Each fiber has multiple nuclei, glycogen and myoglobin. Myoglobin stores oxygen and helps to break down glycogen for generation of ATP required for muscle contraction. Sarcolemma is the plasma membrane of the muscle fiber and helps in impulse conduction. Each muscle fiber is composed of a functional unit called Sarcomere which is the basic unit of muscle contraction.
Each sarcomere is composed of mitochondria, Sarcoplasm (cytoplasm of muscle fiber), and transverse tubules (extensions of Sarcolemma), sarcoplasmic reticulum (endoplasmic reticulum of muscle) and terminal cisternae. The sarcoplasmic reticulum (endoplasmic reticulum of muscle) and terminal cisternae liberates calcium ions necessary for muscle contraction.

Sarcoplasm contains myofibrils that are composed of thick filaments, thin filaments and Titin. Titin stabilizes the attachment of Actin at individual Z lines. Thin myofilaments are composed of the structural protein called Actin and regulatory proteins called Troponin and Tropomyosin. Upon the liberation of calcium ions from the sarcoplasmic reticulum, Troponin senses calcium and pulls Tropomyosin into the groove of the Actin filaments. This helps in cross-bridge formation between Actin and Myosin. Cleavage of ATP generates the power stroke causing shortening or contraction of the individual muscle fiber.