The Muscular SystemWhat is the Muscular System?Overview of Muscles TypesOverview of Muscle Types Body LocationOverview of Muscle Types Cell Shape and AppearanceSkeletal Muscle – Connective Tissue ComponentTendonsReview of Skeletal MuscleReview of Smooth MuscleReview of Cardiac MuscleMuscle FunctionsMuscle Functions - SkeletalAnatomy of Skeletal MuscleLet’s zoom in . . .MyofilamentsStimulation of Muscle - TermsNerve StimulusNeuromuscular JunctionWhat’s going on in cleft?ACh bindingWhat happens to ACh?How does muscle cell return to resting state?Muscle Contraction The Sliding Filament TheoryActual Chemical ProcessSliding ActionSliding Action Cont’dContraction of Sk. Muscle as a WholeHow do Graded Responses Happen?Different Rates of StimulationMuscle Response to Stronger StimuliThe EndThe Muscular SystemChapter 6What is the Muscular System?•What is it?•What is the essential function of muscle tissue?•Muscles are the “machines” of the bodyOverview of Muscles Types•3 Types–Cardiac–Skeletal–Smooth•Differ in cell structure, location, how stimulated to contract•What are similarities?–Muscle Fibers = skeletal and smooth, elongated–Contraction – two types of myofilaments (microfilaments)–myo, mys, sarco – relates to muscle, sarcoplasmOverview of Muscle TypesBody Location •Skeletal Muscle – attaches to bones, smooth contours of body, voluntary•Smooth Muscle – walls of hollow visceral organs, stomach, bladder, respiratory tract, GI, involuntary•Cardiac Muscle – heart, forms bulk to heart walls, involuntaryTable 6.1 (1 of 2)Overview of Muscle Types Cell Shape and Appearance•Skeletal – huge fibers, cigar-shaped, multinucleate, striated•Smooth – spindle-shaped, uninucleate, often found in layers, no striations•Cardiac – striated, branching cells joined by intercalated discsSkeletal Muscle – Connective Tissue Component•Can exert a lot of power, how?•Fibers bundled together by CT, support and protection•Endomysium – covers individual fibers•Perimysium – coarser fibers, covers a few fibers called fascicle•Epimysium – even tougher, many fascicles, covers entire muscle–Blends with either tendon or aponeuroses, attach muscle to bone, cartilage, CTFigure 6.1Tendons•Tendons –Anchor muscle to bone–Provide durability, conserve space–Mostly tough Collagenic fibers, cover bones–Small size, more can pass over jointReview of Skeletal Muscle•Multinucleate, cigar shaped•Voluntary•Striated•Attach to skeletal system•Contracts rapidly and w/ force, but tires easily•Vary in shape from enlarged belly to flat to fan shapedReview of Smooth Muscle•Spindle shaped, uninucleate•No striations•Involuntary•Visceral•Surrounded by small endomysium•2 layers, longitudinal and circular, alternate contraction•Contraction slow and sustainedFigure 6.2aReview of Cardiac Muscle•Heart•Striated•Involuntary•Small amount of endomysium•Arranged in spiral•Branching cells, intercalated discs–Heart activity coordinated closely•Internal pacemaker, steady contraction but can be stimulated by nervous systemFigure 6.2bMuscle Functions•Producing Movement: all 3 types–Mobility of body, locomotion, manipulation – skeletal, respond quickly to environment, nonverbal communication–Pumping of blood and movement of blood in vessels – heart and smooth muscle, circulate blood, blood pressure–Forces fluid and other substances through internal channels – smooth, urine, bile, food, babyMuscle Functions - Skeletal•Maintaining Posture – tiny adjustments to gravity•Stabilizing Joints – pull on bones for movement, stabilizes joints, tendons•Generating Heat – by-product of muscle activity.–ATP used, ¾ of energy escapes as heat–>40% of body mass, most responsible for heat generationAnatomy of Skeletal Muscle•Sarcolemma = PM, many dark nuclei•Organelles called myofibrils push nuclei to side, perfectly aligned•Light (I) Dark (A) bands alternate, striationsFigure 6.3a–bLet’s zoom in . . .•Myofibril–Light (I) Band•Darker mid-region called Z disc–Dark (A) Band•Lighter mid-region called H zone•M line in center of H zone, proteins rods hold thick filaments together•Sarcomere – 1 functional unit–Myofilaments within sarcomere that generates banding pattern•Sarcoplasmic reticulum – SER, surrounds every myofibril, stores and releases calciumMyofilaments•2 types - proteins–Thick filament = myosin•Extend length of A band•Also contain ATPases, split ATP•Myosin heads, cross bridges–Thin filament = actin•Some regulatory proteins•I band, ends of 2 sarcomeres•Anchored to Z disc (disclike membrane)•H zone lacks actin filaments = bare zone, when relaxed•Result in banding pattern!!!Figure 6.3c–dStimulation of Muscle - Terms•Excitability – receive and respond to stimuli•Contractility – ability to forcibly shorten when stimulated•Extensibility – ability of muscle cells to be stretched•Elasticity – ability to recoil to resting length after stretchNerve Stimulus•Contraction requires nerve impulse•One MOTOR neuron can stimulate a few or 100s of muscle cells = motor unit•Axon – nerve fiber•Axon terminals – sarcolemma of different nerve cells•Neuromuscular junctions•Synaptic Cleft – interstitial fluidFigure 6.4Neuromuscular JunctionFigure 6.5aWhat’s going on in cleft?•Nerve impulse reaches axon terminal, releases neurotransmitter, ACh•ACh diffuses across synaptic cleft•Binds to receptors (membrane proteins) on sarcolemma Figure 6.5bFigure 6.5cACh binding•ACh binding makes sarcolemma more permeable to Na+ and K+ ions•Na+ rush in, K+ out•More Na+ in than K+ reverses normal gradient of sarcolemma•Opens more Na+ channels, allowing ONLY more Na+ in, exaggerating + inside•The reversing of the gradient generates action potential = unstoppable once started–Travels length of cell, results in contractionWhat happens to ACh?•As long as in cleft, will keep stimulating!•Broken down by AChE into acetic acid and choline•Only one contraction per nerve impulse•Must have another round of ACh release for another contractionHow does muscle cell return to resting state?•We just reversed the gradient across the cell membrane (sarcolemma)•How do we get back to a negative interior and a positive exterior?–Diffusion of K+ out of cell–Na+/K+ pump – pumps ions back to initial positionsMuscle ContractionThe Sliding Filament