Physiology of Muscle Contraction, Slides of Human Physiology

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PHYSIOLOGY OF MUSCLE CONTRACTION Prof. Sultan Ayoub Meo MBBS, M.Phil, Ph.D (Pak), M Med Ed (Dundee), FRCP (London), FRCP (Dublin), FRCP (Glasgow), FRCP (Edinburgh) Professor and Consultant, Department of Physiology, College of Medicine, King Saud University, Riyadh, KSA TYPES OF MUSCLES : = Smooth muscle Cardiac muscle Skeletal muscle * has narrow, tapered rod-shaped cells. * has striated, tubular, branched, * has striated, tubular, * has nonstriated, uninucleated fibers. uninucleated fibers. multinucleated fibers. * occurs in walls of internal organs * occurs in walls of heart. * is usually attached to skeleton, and blood vessels. * is involuntary. * is voluntary. * is involuntary. SKELETAL MUSCLE Sarcolemma Dark Light (A) band (I) band (a) Segment of an Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. SKELETAL MUSCLE Z disc Hzone Zdisc Thin (actin) filament Thick (myosin) filament (b) Iband Aband band Mline (complex organelle composed of bundles of myofilaments) Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. |  | SKELETAL MUSCLE (c) ‘Sarcomere (segment of a myofibril) NEURON Dendrites Cell body Axon Collect Integrates incoming Passes electrical signals electrical signalsand generates to dendrites of another signals outgoing signal to cell or to an effector cell axon  4 non Myelinated axon of motor neuron Axon terminal at neuromuscular junction Axon terminal Power Stroke Actin molecules in thin myofilament G3 Binding: Myosin —— cross bridge binds to Myosin cross bridge ——— actin molecule. Z line << © Power stroke: Cross bridge bends, pulling thin myofilament inward. ©& Detachment: Cross bridge detaches at end of power stroke and returns eh to original conformation. G3 Binding: Cross bridge ~_— binds to more distal actin molecule; cycle repeats. SLIDING FILAMENT THEORY When a muscle cell contracts, the thin filaments slide past the thick filaments, and the sarcomere shortens. This process comprised of several steps is called the Sliding Filament Theory. It is also called the Walk Along Theory or the Ratchet Theory. SLIDING FILAMENT THEORY Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Table 12.2 | Summary of the Sliding Filament Theory of Contraction 1. Amyofiber, together with all its myofibrils, shortens by movement of the insertion toward the origin of the muscle. 2. Shortening of the myofibrils is caused by shortening of the sarcomeres—the distance between Z lines (or discs) is reduced. 3. Shortening of the sarcomeres is accomplished by sliding of the myofilaments—the length of each filament remains the same during contraction. 4. Sliding of the filaments is produced by asynchronous power strokes of myosin cross bridges, which pull the thin filaments (actin) over the thick filaments (myosin). 5. The A bands remain the same length during contraction, but are pulled toward the origin of the muscle. 6. Adjacent A bands are pulled closer together as the | bands between them shorten. 7. The H bands shorten during contraction as the thin filaments on the sides of the sarcomeres are pulled toward the middle. 2 Sarcomeres [ 1 H zone | band A band a | : T : 1 ; Thick —— | Z disc Thin filament Z disc M line Z disc (a) Relaxed muscle me (b) Partially contracted muscle (c) Maximally contracted muscle ZEEE] comparison of Skel me 2 os CHARACTERISTIC SKELETAL CARDIAC SMOOTH Presence of gap junctions No Yes; at intercalated discs Yes; in single-unit muscle Cells exhibit individual Yes No Not in single-unit muscle; yes neuromuscular junctions in multiunit muscle Regulation of contraction Voluntary via axon terminals Involuntary; intrinsic system Involuntary; autonomic nerves, of the somatic nervous regulation; also autonomic hormones, local chemicals; system nervous system controls; stretch hormones; stretch Source of Ca?+ for calcium Sarcoplasmic reticulum (SR) SR and from extracellular fluid | SR and from extracellular fluid pulse Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings. Table 9.3.3  CHARACTERISTIC Comparison of Skeletal SKELETAL CARDIAC SMOOTH Site of calcium regulation Presence of pacemaker(s) Effect of nervous system stimulation Speed of contraction Rhythmic contraction Response to stretch Respiration Troponin on actin-containing thin filaments Actin , Troponin No Excitation Slow to fast No Contractile strength increases with degree of stretch (to a point) Aerobic and anaerobic Troponin on actin-containing thin filaments Actin , Troponin Yes Excitation or inhibition Slow [ZN Yes Contractile strength increases with degree of stretch Aerobic Calmodulin in the sarcoplasm Calmodulin -, head Yes (in single-unit muscle only) Excitation or inhibition Very slow aa Se Yes in single-unit muscle Stress-relaxation response Mainly aerobic Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings. Table 9.3.4 Smooth muscle Skeletal muscle ee eee Rise in cytosolic Ca* Rise in cytosolic Ca* (mostly from extracellular (entirely from intracellular fluid) sarcoplasmic reticulum) - Physical repositioning of Series of biochemical events troponin and tropomyosi . Uncovering of cross-bridge Phosphorylation of myosin binding 'sitas on'aciinin in thick filament thin qc Binding of actin and myosin Binding of actin and myosin at cross bridges at cross bridges : © Brooks/Cole - Thomson Learning :