BIOL 460 1st Edition Lecture 16 Outline of Last Lecture I Excitation of Muscle Cells II Length Tension Relationship III Motor Unit Outline of Current Lecture I Muscle Twitch II Skeletal Muscle Fiber Types III Cardiac Muscle IV Smooth Muscle Current Lecture Muscle Twitch 1 Amplitude of twitch is measure of force of contraction 2 Result of recruitment 3 Summation a Causes even stronger contraction than possible with single stimulus b Series elastic elements some of force of twitch is applied to stretch connective tissue some total force is lost c 2nd stimulus occurs when already stretched all force applied to transducer bone 4 Sustained contraction tetanus a No relaxation b Some relaxation incomplete tetanus c Not how muscles in vivo sustain contraction 5 Asynchronous activation of motor units a Each motor unit contracts in a twitch like fashion b Doesn t contract at the same time Skeletal muscle fiber types 1 2 3 4 Classify based on contraction speed and ATP production Contraction speed based on ATPase ability of myosin cross bridges Some achieve maximum tension very quickly some much slower Humans These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 5 6 a Fast twitch 7 5milliseconds b Slow twitch 100 milliseconds Can classify based on principle mechanism of ATP synthesis a Red fibers i Oxidative ii Most ATP generated through redox reactions iii Red because well vascularized iv Have a lot of myoglobin v Many mitochondria b White fiers i Glycolytic ii Produce ATP through glycolysis iii Fermentation iv Final e acceptor is pyruvate v High concentration of glycolytic enzymes vi Larger in diameter Classifications a Slow oxidative slow twitch fatigue resistant i Postural muscles ii Smallest motor units b Fast glycolytic fast twitch fatigueable i Biggest motor units c Fast oxidative fast twitch fatigue resistant i Medium motor units Cardiac Muscle 1 2 3 4 5 6 7 8 9 In heart Striated typical sarcomeres Contract with sliding filament mechanism Innervated by visceral motor neurons Short uninucleate branched cells Attached by gap junctions Intercalated disc discs between cardiac muscle cells 1 AP is quickly spread through all cells in myocardium Myocardium mass of cardiac muscle cells a Atrial myocardium b Ventricular myocardium 10 Myocardium connected via intercalated discs 11 No motor Units 12 Automaticity contracts on its own AP changes resting frequency Smooth Muscle 1 Innervated by autonomic neurons 2 Two types a Multiunit iris of eye individual smooth muscle cells all receiving innervation by one axon b Single Unit i Much more common ii Walls of hollow organs iii Innervation by synapses en passant iv Cells are connected together with gap junctions v All contract together vi Generate peristaltic waves 3 Non striated no A and I bands no sarcomeres 4 Cells are spindle shaped uninucleate 5 No z discs thin filaments attach to sarcolemma or masses of protein called dense bodies 6 Thick myofilaments are less common much more actin than myosin 16 1 ratio 7 Thick myofilaments are composed of myosin organized with cross bridges parallel to shaft unlike skeletal muscle 8 No bare zone without cross bridges 9 LOOK AT FIGURE 12 37 10 Single unit SM innervation occurs via gap junctions 11 Smooth muscle a More thin thick ratio 16 1 than skeletal muscle 2 1 b No bare zone on thick myofilament c Cross bridges parallel to myosin band d Makes smooth muscle better able to stretch e Slow sustained contractions slow myosin ATPase s 12 Excitation Contraction coupling in Smooth muscle a Trigger is Ca2 from extracellular environment NOT FROM SR b Sarcolemma contains Ca2 VGC c EPSPs Graded contractions result of amount of Ca2 going in cell i Low Ca2 weak contraction ii High Ca2 strong contraction d No troponin or tropomyosin e Ca2 in cell bonds to calmodulin making Ca2 calmodulin complex f Activates myosin light chain kinase g Phosphorylates myosin light chains h Cross bridges attach to thin myofilaments and cross bridge cycle i Turning contraction of i Ca2 pumped out of sarcoplasm via Ca2 pumps ii Myosin phosphatase dephosphorylates myosin light chains