Skeletal Muscle Contraction Year 1 Biology II PDF 2023 - 2024

Skeletal Muscle Contraction Year 1 - Biology II 2023 - 2024 Dr. Rima Abdul Razzaq Function of Skeletal Muscle we control ↑ Skeletal muscles are voluntary muscles under the control of the somatic nervous system. Over 650 skeletal muscles in the human body, making up around 40% of body weight. 1. 2. 3...

Skeletal Muscle Contraction Year 1 - Biology II 2023 - 2024 Dr. Rima Abdul Razzaq Function of Skeletal Muscle we control ↑ Skeletal muscles are voluntary muscles under the control of the somatic nervous system. Over 650 skeletal muscles in the human body, making up around 40% of body weight. 1. 2. 3. 4. 5. 6. Upright posture and balance: Continuous contraction of lower leg muscles to counterbalance the effect of gravity. Body movement. Movement of bones and other body structures. Production and maintenance of body heat: Breakdown of ATP required for muscle contraction produces heat. Skeletal muscle pump: Pumps blood in veins and lymph back to the heart. Protection of internal organs. Facial muscles produce the facial expressions. smakes us straight. stand Skeletal Muscle and Body Movement When skeletal muscles contract, bones move. e Muscles move the body by contracting against the skeleton. Muscle contract - Shorten > - more Muscles attached by tendons to bones of the skeleton. Force is transmitted from the muscle cells to the tendon. When muscles contract, they get shorter. By contracting, muscles pull on the tendons and bones and allow the body to move. How Skeletal Muscles Function 9 muscles in can only be neutral position , or contracted Skeletal muscles work in pairs Skeletal muscles function in groups Muscles can only contract, so they can only pull. They cannot actively extend (push), though they can move or relax back into the non-contracted neutral position. Antagonist muscle acts opposite to the prime mover. To move bones in opposite directions, pairs of muscles must work in opposition. Agonist muscle: Prime mover Synergist muscles act around a joint to help the action of an agonist muscle. when flexing biceps : arm Prime > Synergetics that muscles helps prime around muscle agonist antagonist antagonist agonist Skeletal Muscle Structure Skeletal muscle cells are long and cylindrical, they are commonly referred to as muscle muscle fibers. fiber = muscle cell Inside each skeletal muscle, muscle fibers are organized into bundles, called fascicles, fasicles fiber grouped together fasicles surrounded by a middle layer of connective Perimysium fiber endomysium-inside fasicle tissue called the perimysium. = muscle = fissue that surrounds , each muscle is enclosed by this See this T Inside each fascicle, each muscle fiber is encased in a thin connective tissue layer called the endomysium. The endomysium surrounds the extracellular matrix of the cells and plays a role in transferring force produced by the muscle fibers to the tendons. Muscle fiber is cylindrical, containing many myofibrils. many myofibrils make muscle fiber Details of Skeletal Muscle Fibers It's multinucleated M In addition to nuclei, skeletal muscle fibers also contain cellular organelles found in other cells. important because it releases calcium ions stores Mitochondria > too many - needs energy Cytoplasm is referred to as sarcoplasm. muscle cytoplasm sarcoplasm Cell membrane of muscle fibers is called the sarcolemma (plasmalemma). Sarcolemma forms T (transverse) tubules, which are extensions of the cell membrane that penetrate into the centre of the skeletal muscle cells. d = muscle cell membrane Specialized smooth endoplasmic reticulum, called the sarcoplasmic reticulum (SR), stores, releases, and retrieves calcium ions (Ca++). sarcolemma , Plasmalemma Myofibrils and Sarcomeres muscle cells contain filaments and they are the contractile portion of the cell Myofibrils contain the myofilaments, so they are the contractile portions of the muscle fibers. · Within a muscle fiber, myofibrils run the length of the cell and contain sarcomeres connected in series. myofibrils -> cell length 3 Contain sarcomere The sarcomere Smallest functional unit of a skeletal muscle fiber. The striated appearance of skeletal muscle fibers is due to the arrangement of the thick and thin myofilaments within each sarcomere. The dark striated A band is composed of the thick filaments containing myosin, which span the center of the sarcomere extending toward the Zdics. The lighter I band regions contain thin actin filaments anchored at the Z-discs. It is the shortening of individual sarcomeres that leads to the contraction of individual skeletal muscle fibers. one one muscle cell Stopped were Myofilament Components myosin protein make thick myofilaments Thick myofilaments are composed of myosin protein complexes. The tail straight portion ends in a globular head or cross bridge. Globular head contains an actin-binding site and a binding site for the high-energy molecule ATP (ATPase). Hundreds of myosin proteins are arranged into each thick filament with tails toward the M-line and heads extending toward the Z-discs. head : globular - - active site binding site for Atpase Thin myofilaments consist of 2 intertwining strands of the protein actin. Thin myofilaments -consist 2 intertwining of Within the filament, each actin monomer contains a myosin binding site and is also associated with the regulatory proteins, troponin and tropomyosin. strand of protein actin each strand myosin consist of binding site X associated with proteins (troponin 3, tropomyosin) Troponin and tropomyosin run along the actin filaments and control when the actin binding sites will be exposed for binding to myosin. contraction = sliding of filaments The Sliding Filament Model of Contraction zline : moves closer together I band : becomes smaller a Aband : same width