9Force of Muscle ContractionSlide 3Slide 4Slide 5Velocity and Duration of ContractionMuscle Fiber TypeSlide 8Slide 9Slide 10Slide 11Effects of ExerciseEffects of Resistance ExerciseThe Overload PrincipleSmooth MuscleSlide 16PeristalsisMicroscopic StructureSlide 19Slide 20Innervation of Smooth MuscleSlide 22Myofilaments in Smooth MuscleSlide 24Slide 25Slide 26Contraction of Smooth MuscleSlide 28Role of Calcium IonsSlide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Regulation of ContractionSlide 41Special Features of Smooth Muscle ContractionSlide 43Types of Smooth MuscleTypes of Smooth Muscle: MultiunitMuscular DystrophySlide 47PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal CollegeC H A P T E RCopyright © 2010 Pearson Education, Inc.9Muscles and Muscle Tissue: Part CCopyright © 2010 Pearson Education, Inc.Force of Muscle Contraction•The force of contraction is affected by:•Number of muscle fibers stimulated (recruitment)•Relative size of the fibers - hypertrophy of cells increases strengthCopyright © 2010 Pearson Education, Inc.Force of Muscle Contraction•The force of contraction is affected by:•Frequency of stimulation - frequency allows time for more effective transfer of tension to noncontractile components•Length-tension relationship - muscles contract most strongly when muscle fibers are 80–120% of their normal resting lengthCopyright © 2010 Pearson Education, Inc.Figure 9.21Largenumber ofmusclefibersactivatedContractile forceHighfrequency ofstimulationLargemusclefibersMuscle andsarcomerestretched to slightly over 100%of resting lengthCopyright © 2010 Pearson Education, Inc.Figure 9.22SarcomeresgreatlyshortenedSarcomeres atresting lengthSarcomeres excessivelystretched170%Optimal sarcomereoperating length(80%–120% ofresting length)100%75%Copyright © 2010 Pearson Education, Inc.Velocity and Duration of ContractionInfluenced by:1. Muscle fiber type2. Load3. RecruitmentCopyright © 2010 Pearson Education, Inc.Muscle Fiber TypeClassified according to two characteristics:1. Speed of contraction: slow or fast, according to:•Speed at which myosin ATPases split ATP•Pattern of electrical activity of the motor neuronsCopyright © 2010 Pearson Education, Inc.Muscle Fiber Type2. Metabolic pathways for ATP synthesis:•Oxidative fibers—use aerobic pathways•Glycolytic fibers—use anaerobic glycolysisCopyright © 2010 Pearson Education, Inc.Muscle Fiber TypeThree types: •Slow oxidative fibers•Fast oxidative fibers•Fast glycolytic fibersCopyright © 2010 Pearson Education, Inc.Table 9.2Copyright © 2010 Pearson Education, Inc.Figure 9.23Predominanceof fast glycolytic(fatigable) fibersPredominanceof slow oxidative(fatigue-resistant)fibersSmall loadContractilevelocityContractiledurationCopyright © 2010 Pearson Education, Inc.Effects of ExerciseAerobic (endurance) exercise:•Leads to increased:•Muscle capillaries•Number of mitochondria•Myoglobin synthesis•Results in greater endurance, strength, and resistance to fatigue• May convert fast glycolytic fibers into fast oxidative fibersCopyright © 2010 Pearson Education, Inc.Effects of Resistance Exercise•Resistance exercise (typically anaerobic) results in:•Muscle hypertrophy (due to increase in fiber size)•Increased mitochondria, myofilaments, glycogen stores, and connective tissueCopyright © 2010 Pearson Education, Inc.The Overload Principle•Forcing a muscle to work hard promotes increased muscle strength and endurance•Muscles adapt to increased demands•Muscles must be overloaded to produce further gainsCopyright © 2010 Pearson Education, Inc.Smooth Muscle•Found in walls of most hollow organs(except heart)•Usually in two layers (longitudinal and circular)Copyright © 2010 Pearson Education, Inc.Figure 9.26Smallintestine(a)(b) Cross section of theintestine showing thesmooth muscle layers(one circular and theother longitudinal)running at rightangles to each other.MucosaLongitudinal layerof smooth muscle (shows smooth muscle fibers in cross section)Circular layer ofsmooth muscle (shows longitudinalviews of smooth muscle fibers)Copyright © 2010 Pearson Education, Inc.Peristalsis•Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through the lumen of hollow organs•Longitudinal layer contracts; organ dilates and shortens •Circular layer contracts; organ constricts and elongatesCopyright © 2010 Pearson Education, Inc.Microscopic Structure•Spindle-shaped fibers: thin and short compared with skeletal muscle fibers•Connective tissue: endomysium only•SR: less developed than in skeletal muscle •Pouchlike infoldings (caveolae) of sarcolemma sequester Ca2+•No sarcomeres, myofibrils, or T tubulesCopyright © 2010 Pearson Education, Inc.Table 9.3Copyright © 2010 Pearson Education, Inc.Table 9.3Copyright © 2010 Pearson Education, Inc.Innervation of Smooth Muscle•Autonomic nerve fibers innervate smooth muscle at diffuse junctions•Varicosities (bulbous swellings) of nerve fibers store and release neurotransmittersCopyright © 2010 Pearson Education, Inc.Figure 9.27SmoothmusclecellVaricosities releasetheir neurotransmittersinto a wide synaptic cleft (a diffuse junction).SynapticvesiclesMitochondrionAutonomicnerve fibersinnervatemost smoothmuscle fibers.VaricositiesCopyright © 2010 Pearson Education, Inc.Myofilaments in Smooth Muscle•Ratio of thick to thin filaments (1:13) is much lower than in skeletal muscle (1:2)•Thick filaments have heads along their entire length•No troponin complex; protein calmodulin binds Ca2+Copyright © 2010 Pearson Education, Inc.Myofilaments in Smooth Muscle•Myofilaments are spirally arranged, causing smooth muscle to contract in a corkscrew manner•Dense bodies: proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervalsCopyright © 2010 Pearson Education, Inc.Figure 9.28aCopyright © 2010 Pearson Education, Inc.Figure 9.28bCopyright © 2010 Pearson Education, Inc.Contraction of Smooth Muscle•Slow, synchronized contractions •Cells are electrically coupled by gap junctions•Some cells are self-excitatory (depolarize without external stimuli); act as pacemakers for sheets of muscle •Rate and intensity of contraction may be modified by neural and chemical stimuliCopyright © 2010 Pearson Education, Inc.Contraction of Smooth Muscle•Sliding filament mechanism•Final trigger is  intracellular