Sceletal Muscle Study Resources

University:
Franklin University
Course:
BIO-251 | General Anatomy/Physiology I
Academic year:

2019
Views:

99

Pages:

22
Author:

NovaNurturer

Introduction Skeletal muscle most  abundant tissue in the human body (40-45% of total body weight) Human body has more than 430 pairs of skeletal muscle Embryologic origin: Skeletal Muscle Is actually a multinucleated syncytium.  In cross section, reveals a polygonal shape with a diameter of 10 – 100 μm .  Their varies from almost a meter (sartorius) to as little as a few millimeters(stapedius)  Muscle fiber Organization of myofilaments I: Structure of Skeletal Muscle: The Sarcomere  Further divisions of myofibrils in polarizing microscopy ◦ A-band = Dark bands = Birefringent = Anisotropic ◦ I-band = light band = Monorefringent = Isotropic ◦ Z line = between disks ◦ H band = Hell light ◦ M line = Mitte= Middle Myofilament  Two types of myofilaments are associated with cell contraction Thin filament  Thick filament  Thin filaments Thin filament contain :  F actin  Tropomyosin  Troponin F actin     G actin is a small, 42 KD molecule that polymerizes to form a doublestranded helix, the F-actin filament. These actin filaments are polar; all G-actin molecules are oriented in same direction. The plus end of each filament is bound to the Z line by α-actinin; the minus end extends toward the M line and is protected by actine – capping protein. Each G-actin has a binding site for myosin. Tropomyosin Toropomyosin is a 64 KD protein that also consists of a double helix of two polypeptides.  In resting muscle, the troponin complex, mask the myosin – binding site on the actine molecule.  Troponin      Troponin actually consists of a complex of three globular subunits. Each tropomyosin molecule contains one troponin complex. Troponin-C (TnC) is the smallest subunit 18 KD, binds Ca ,the essential step in the initiation of contraction. Troponin-T (TnT) , 30 KD binds to tropomyosin Troponin I (TnI) , 30 KD binds to actin , thus inhibiting actin – myosin interaction. Figure 10–13. Schematic representation of the thin filament, showing the spatial configuration of 3 major protein components—actin, tropomyosin, and troponin. The individual components in the upper part of the drawing are shown in polymerized form in the lower part. The globular actin molecules are polarized and polymerize in one direction. Note that each tropomyosin molecule extends over 7 actin molecules. TnI, TnC, and TnT are troponin subunits. Thick filament 15 nm in diameter,1.5 μm long, composed of the protein myosin II.  Each thick filament consists of 200-300 myosin molecules.   Each heavy chain has a small globular head that projects at an approximately right angle at one end of the long rod-shaped molecule.  This globular head has two specific binding sites ,one for ATP and one for actin. It also demonstrates ATPase and motor activity.   The phospholylation by myosin light chain kinase of regulatory might chain initiates contraction in smooth muscles. Accessory proteins           These strustural proteins less than 25% of the total protein of muscle fiber. They include: Titin α-actinin Nebulin Tropomudulin Desmin Myomesin C protein Dystrophin Sarcomer = functional unit It is the portion of a myofibril between two adjacent Z lines.  A sarcomere measures 2-3 μm in relaxed mammalian muscle.  It may be stretched to more 4 μm during extreme contraction, may be reduced to as little as 1 μm.  Z line Z line

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