Muscular tissue

1. Muscular tissue • Consist of elongated cells called muscle fibers or myocytesthat can use ATP to generate force by its contractile proteins. • Functions: • Movements. • Maintains posture. • Generates heat. • Provides protection. • Types: Classified into 3 types according to their location, structural and functional characteristics. • Skeletal. • Cardiac. • Smooth.

2. 1- Skeletal Muscle Each skeletal muscle is a separate organ composed of hundreds to thousands of cells, which are called Muscle Fibers muscle cell and muscle fiber are two terms for the same structure

3. 1-Sarcolemma the plasma membrane of a muscle cell The structure of the muscle fibers or myocytes 2- thesarcoplasmis the cytoplasm of a muscle fiber 3-Sarcoplasmic reticulum A fluid-filled system of membranous sacs similar to smooth endoplasmic reticulum Contains a-glycogen, which is a large molecule b-myoglobin : protein, found only in muscle. c- mitochondria

4. Within the muscle fiber smaller protein structures called myofilaments 1-Thin filaments called Protein actin 2- Thick filaments called the Protein myosin.

5. The filaments are arranged in compartments called SARCOMERES which are the basic functional units of a myofibril Z discs Narrow regions separate one sarcomere from the next The sarcomere extends from one Z disc to the next Z disc.

6. The Sliding Filament Mechanism Muscle contraction occurs because myosin heads attach to and “walk” along the thin filaments at both ends of a sarcomere.` As a result, the thin filaments slide inward and meet at the center of a sarcomere. They may even move so far inward that their ends overlap As the thin filaments slide inward, and the sarcomere shortens. Shortening of the sarcomeres causes shortening of the whole muscle fiber, which in turn leads to shortening of the entire muscle.

7. 2- Smooth muscle • Composed of spindle-shaped, nonstriated cells containing single, central nucleus. • Involuntary. • Location:walls of hollow structures as stomach and blood vessels. • Function: • Constrictione.g. blood vessels. • Propulsion of foodse.g. stomach • Contraction e.g. UB

8. Within each fiber is a single, oval, centrally located nucleus. • The sarcoplasm of smooth muscle fibers contains both • thick filaments and thin filaments • but they are not arranged • in orderly • sarcomeres as in striated muscle. • Smooth muscle fibers do not exhibit striations causing a smooth appearance. • have only a small amount of sarcoplasmic reticulum for storage of Ca. for muscular contraction.

9. In smooth muscle fibers, the thin filaments attach to structures called dense bodies which are functionally similar to Z discs in striated muscle fibers. Bundles of intermediate filaments also attach to dense bodies and stretch from one dense body to another. During contraction, the sliding filament mechanism involving thick and thin filaments generates tension that is transmitted to intermediate filaments. These in turn pull on the dense bodies attached to the sarcolemma, causing a shortening of the muscle fiber. As a smooth muscle fiber contracts, it rotates. The fiber twists as it contracts, and rotates in the opposite direction as it relaxes.

10. 3-Cardiac muscle