Presentation on theme: "Chapter 10: Muscle Tissue"— Presentation transcript:
1 Chapter 10: Muscle Tissue AnnMarie Armenti, MS SCCC BIO 130
2 Muscle Tissue A primary tissue type, divided into: skeletal muscle Voluntary striated muscle, controlled by nerves of the central nervous systemcardiac muscleInvoluntary striated musclesmooth muscleInvoluntary nonstriated muscle
3 Characteristics of all Muscle Tissues Specialized Cells:- elongated, high density of myofilaments = cytoplasmic microfilaments of actin and myosinExcitability/Irritability:- receive and respond to stimulusContractility:- shorten and produce force upon stimulationExtensibility:- can be stretchedElasticity:- recoil after stretch
4 Skeletal Muscle Tissue Skeletal muscles make up 44% of body massSkeletal muscle = an organcomposed of:skeletal muscle cells (fibers) and CTnerves and blood vessels
5 Functions of Skeletal Muscles Produce skeletal movementMaintain posture and upright positionSupport soft tissuesGuard entrances and exitsMaintain body temperature by generating heatStabilize joints
7 Formation of Skeletal Muscle Fibers Skeletal muscle cells are called fibersFigure 10–2
8 Skeletal Muscle Anatomy Each muscle is innervated by one nerve:Nerve must branch and contact each skeletal muscle fiber (cell)One artery, branches into extensive capillaries around each fiber:supply oxygensupply nutrientsremove wastes.
10 Organization of Connective Tissues Muscles have 3 layers of connective tissues that hold the muscle together:Epimysium- covers the muscle (exterior collagen layer), separates muscle from other tissues, composed of collagen, connects to deep fasciaPerimysium- composed of collagen and elastin, has associated blood vessels and nerves, bundles muscle fibers into groups called fascicles- perimysium covers a fascicleEndomysium- composed of reticular fibers, contains capillaries, nerve fibers and satellite cells (= stem cells repair), surrounds individual muscle fibers
11 Muscle AttachmentsEndomysium, perimysium, and epimysium come together:at ends of musclesto form connective tissue attachment to bone matrixTendon = cord-like bundlesAponeurosis = sheet-like
12 How would severing the tendon attached to a muscle affect the muscle’s ability to move a body part? Uncontrolled movement would result from a severed tendon.Movement would be greatly exaggerated with no tendon.No movement is possible without a muscle to bone connection.Limited movement would result.
14 Skeletal Muscle Fibers Huge cells:up to 100 µm diameter, 30 cm longMultinucleateFormed by fusion of 100s of myoblastsNuclei of each myoblast retained to provide enough mRNA for protein synthesis in large fiberUnfused myoblasts in adult = satellite cellsSatellite cells are capable of division and fusion to existing fibers for repair but cannot generate new fibers
15 Organization of Skeletal Muscle Fibers Figure 10–3
16 Skeletal Muscle Fibers Cell membrane = sarcolemmaSarcolemma maintains separation of electrical charges resulting in a transmembrane potentialNa+ pumped out of the cell creating positive charge on the outside of the membraneNegative charge from proteins on inside give muscle fibers a resting potential of -85mVIf permeability of the membrane is altered, Na+ will flow in causing a change in membrane potentialChange in potential will signal the muscle to contract
17 Transverse TubulesTubes of sarcolemma called transverse tubules (T tubules) reach deep inside the cell to transmit changes in transmembrane potential to structures inside the cellTransmit action potential through cellAllow entire muscle fiber to contract simulataneously
18 Skeletal Muscle Fibers Cytoplasm = sarcoplasm:rich in glycosomes (glycogen granules) and myoglobin (binds oxygen)Fiber is filled with myofibrils extending the whole length of the cellMyofibrils consist of bundles of myofilamentsMyofilaments are responsible for muscle contractionmade of actin and myosin proteins80% of cell volume
19 Organization of Skeletal Muscle Fibers Figure 10–3
20 Skeletal Muscle Fibers Actin:makes up the thin filamentMyosin:makes up the thick filamentWhen thick and thin filaments interact, contraction occurs
21 Skeletal Muscle Fibers Sarcoplasm contains networks of SER called sarcoplasmic reticulum (SR)Sarcoplasmic Reticulum:A membranous structure surrounding each myofibrilFunction:store calcium and help transmit action potential to myofibrilSR forms chambers (terminal cisternae) attached toT-tubulesCisternaeConcentrate Ca2+ (via ion pumps)Release Ca2+ into sarcomeres to begin muscle contractionAll calcium is actively pumped from sarcoplasm to SR (SR has 1000X more Ca2+ than sarcoplasm)
22 Skeletal Muscle Fibers Triads are located repeated along the length of myofilamentsTriads = T-tubule wrapped around a myofibril sandwiched between two terminal cisternae of SRFormed by 1 T tubule and 2 terminal cisternae of SRTriads are located on both ends of a sarcomereSarcomere = smallest functional unit of a myofibril
26 Sarcomeres The contractile units of muscle Structural units of myofibrilsForm visible patterns within myofibrils
27 Sarcomeres Composed of: 1. Thick filaments – myosin 2. Thin filaments – actin3. Stabilizing proteins:-hold thick and thinfilaments in place4. Regulatory proteins:- control interactions ofthick and thin filamentsOrganization of the proteins in sarcomere causes striated appearance of the muscle fiberFigure 10–4
28 Muscle Striations A striped or striated pattern within myofibrils: alternating dark, thick filaments (A bands) and light, thin filaments (I bands)
29 Regions of the Sarcomere A-band:- whole width of thick filaments, looks darkmicroscopicallyM line: at midline of sarcomere- Center of each thick filament, middle of A-band- Attaches neighboring thick filamentsH-zone:- Light region on either side of the M line- Contains thick filaments onlyZone of overlap:- ends of A-bands- place where thin filaments intercalate between thickfilaments (triads encircle zones of overlap)
30 Regions of the Sarcomere I-band:- Contains thin filaments outside zone of overlap- Not whole width of thin filamentsZ lines/disc:- the centers of the I bands- constructed of Actinins- Anchor thin filaments and bind neighboring sarcomeres- Constructed of Titin Proteins- Bind thick filaments to Z-line, stabilize thefilament
32 Why does skeletal muscle appear striated when viewed through a microscope? Z lines and myosin filaments align within the tissue.Glycogen reserves are linearly arranged.Capillaries regularly intersect the myofibers.Actin filaments repel stain, appearing banded.
33 Sarcomere Function Muscle Contraction Transverse tubules encircle the sarcomere near zones of overlapCa2+ released by SR causes thin and thick filaments to interactMuscle ContractionIs caused by interactions of thick and thin filamentsStructures of protein molecules determine interactions
35 Thin Filaments (5-6 nm diameter) Made of 4 proteins:ActinNebulinHolds F actin strands togetherF-actin (filamentous) consists of rows of G-actin (globular)Each G-actin has an active site that can bind to myosinTropomyosin- Covers the active sites on G actin to prevent actin–myosin bindingTroponin: holds tropomyosin on the G-actinAlso has receptor for Ca2+:when Ca2+ binds to the troponin-tropomyosin complex it causes the release of actin allowing it to bind to myosin
39 Thick Filaments (10-12 nm diameter) Composed of:bundled myosin moleculestitin strands that recoil after stretchingEach Myosin has three parts1. Tail:- tails bundled together to make length ofthick filament- all point toward M-line2. Hinge:- flexible region, allows movement forcontraction
40 Thick Filaments (10-12 nm diameter) 3. Head:- hangs off tail by hinge, will bind actin at activesite.- No heads in H-zone- also contains core of titin:- elastic protein that attaches thickfilaments to Z-line- Titin holds thick filament in place and aidelastic recoil of muscle after stretching- Each thick filament is surrounded by ahexagonal arrangement of thin filaments withwhich it will interact
44 Sliding Filament Theory Contraction of skeletal muscle is due to thick filaments and thinfilament sliding past each othernot compression of the filamentsH-zones and I-bands decrease width during contractionZones of overlap increase widthZ-lines move closer togetherA-band remains constantSliding causes shortening of every sarcomere in every myofibril in every fiberOverall result = shortening of whole skeletal muscle
45 The components of the neuromuscular junction, and the events involved in the neural control of skeletal muscles.
47 Excitation and the Neuromuscular Junction Excitation of muscle fiber is controlled by the nervous system at the neuromuscular junction using neurotransmitter
48 The Neuromuscular Junction Is the location of neural stimulationAction potential (electrical signal):travels along nerve axonends at synaptic terminal
49 Components of Neuromuscular Junction - where a nerve terminal interfaces with a muscle fiber atthe motor end plate- one junction per fiber: control of fiber from one neuronSynaptic Terminal:- expanded end of the axon, contains vesicles ofneurotransmitters Acetylcholine (Ach)Motor End Plate:- specialized sarcolemma that contains Ach receptorsand the enzyme acetylcholinesterase (AchE)Synaptic Cleft:- space between the synaptic terminal and motor endplate where neurotransmitters are released
50 Skeletal Muscle: Neuromuscular Junction Figure 10–10a, b (Navigator)
53 The Neurotransmitter Acetylcholine or ACh: travels across the synaptic cleftbinds to membrane receptors on sarcolemma (motor end plate)causes sodium–ion rush into sarcoplasmis quickly broken down by enzyme (acetylcholinesterase or AChE)
54 Action Potential Generated by increase in sodium ions in sarcolemma Travels along the T tubulesLeads to excitation–contraction coupling
55 The Process of Contraction Neural stimulation of sarcolemma:causes excitation–contraction couplingCisternae of SR release Ca2+:which triggers interaction of thick and thin filamentsconsuming ATP and producing tension
56 3. Excitation–Contraction Coupling Action potential reaches a triad:releasing Ca2+triggering contractionRequires myosin heads to be in “cocked” position:loaded by ATP energy
57 The key steps involved in the contraction of a skeletal muscle fiber.
58 Exposing the Active Site The action potential of the transverse tubules reaches a triad and causes the release of calcium ions from the cisternae of the SR into the sarcoplasm around the zones of overlap of the sarcomeresCalcium binds to troponin on the thin filamentsTroponin pulls tropomyosin off the active sites of the actin so that cross bridges can form.Figure 10–11
60 5 Steps of the Contraction Cycle Exposure of active sitesFormation of cross-bridgesPivoting of myosin headsDetachment of cross-bridgesReactivation of myosin
61 The Contraction Cycle1. Actin, free of tropomyosin, binds to myosin via its active site2. Cross bridges are formed* Actin active sites arebound to myosin headsFigure 10–12 (2 of 4)
62 The Contraction CycleMyosin heads have been pre-primed for movement via ATP energy prior to cross bridge formation and are pointed away from the M line.Upon actin binding, the myosin heads pivot toward the M line in an event called the power stroke, which pulls the thick filament along the thin filamentFigure 10–12 (3 of 4)
63 The Contraction CycleMyosin ATPase uses ATP to break the cross bridges releasing the myosin head from the actin active site, and resets the myosin head pointed away from the M-line
64 The Contraction CycleThe myosin head is now primed to interact with a new active site on actinMyosin can carry out 5 power strokes per second while calcium and ATP are available.Each power stroke shortens the sarcomere by 1%Figure 10–12 (Navigator) (4 of 4)
66 Contraction Duration Depends on: duration of neural stimulus number of free calcium ions in sarcoplasmavailability of ATP
67 4. Relaxation Ca2+ reabsorbed by sarcoplasmic reticulum Ca2+ ions detach from troponinTroponin, without Ca2+, pivots tropomyosin back onto active sites on actin, no cross bridges can formSarcomeres stretch back out:GravityOpposing muscle contractionsElastic recoil of titin proteinResult: Muscle returns to Resting Length
68 A Review of Muscle Contraction Table 10–1 (1 of 2)
69 A Review of Muscle Contraction Table 10–1 (2 of 2)
70 Rigor Mortis A fixed muscular contraction after death Caused when: SR can not absorb Ca2+ :ion pumps cease to functioncalcium builds up in the sarcoplasmCa2+ bind troponinTropomyosin frees actinCross bridges fromNo ATP to detach myosin head because ATP is already all used upfixed cross bridgeContractions occur until necrosis releases lysosomal enzymes which digest cross bridges
71 Disease of Muscle Contraction Botulism/Botox:Bacteria Clostridium botulinum (grows in improperly canned foods) produces botulinum toxinToxin prevents the release of Ach at the neuromuscular junctionResults in flaccid paralysisTetanus:Bacteria Clostridium tetani (grows in soil) produces tenanus toxin:Toxin causes over stimulation of motor neuronsResults in spastic paralysisMyasthenia gravis:Autoimmune diseaseCauses loss of Ach receptors muscles becomenon-responsive
72 KEY CONCEPTSkeletal muscle fibers shorten as thin filaments slide between thick filamentsFree Ca2+ in the sarcoplasm triggers contractionSR releases Ca2+ when a motor neuron stimulates the muscle fiberContraction is an active processRelaxation and return to resting length is passive
73 Where would you expect the greatest concentration of Ca2+ in resting skeletal muscle to be? T tubulessurrounding the mitochondriawithin sarcomerescisternae of the sarcoplasmic reticulum
74 How would a drug that interferes with cross-bridge formation affect muscle contraction? interferes with contractionslows contractionspeeds contractionincreases strength of contraction
75 Predict what would happen to a muscle if the motor end plate failed to produce acetylcholinesterase. Muscle would lose strength.Muscle would be unable to contract.Muscle would lock in a state of contraction.Muscle would contract repeatedly.
76 What would you expect to happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to Ca2+?increased strength of contractiondecreased cross bridge formationdecreased ability to relaxboth A and C
77 The mechanism responsible for tension production in a muscle fiber, and the factors that determine the peak tension developed during a contraction.
78 Tension Production Muscle tension: Force exerted by contracting muscleForce is applied to a loadLoad = weight of the object being acted uponFor a single muscle fiber contraction is all–or–none:as a whole, a muscle fiber is either contracted or relaxed
79 Tension of a Single Muscle Fiber Once contracting tension depends on:1. The number of pivoting cross-bridgesThe fiber’s resting length at the time ofstimulation3. The frequency of stimulation
80 Resting Length Greatest tension produced at optimal resting length Optimal resting length = Optimum overlapOverlap determines the number of pivoting cross-bridgesEnough overlap, so that myosin can bind actin, not so much that thick filaments crash into Z-linesFigure 10–14
81 Why is it difficult to contract a muscle that has been overstretched? Myosin filaments break.Crossbridges can not be formed.Z lines are unable to sustain contractile forces.Tendons lose elasticity.
82 Frequency of Stimulation Twitch = single contraction due to a single neural stimulation, 3 phases:Latent period: post stimulation but no tensionAction potential moves across the sarcolemmaCa2+ is releasedContraction phase: peak tension production- Ca2+ bind- Active cross bridge formationRelaxation phase: decline in tensionCa2+ is reabsorbedCross bridges decline
84 Twitch Single twitch will not produce normal movement requires many cumulative twitchesRepeat stimulation will result in higher tension due to Ca2+ not being fully absorbed- Ca2+ more cross bridgesTypes of Frequency StimulationTreppeWave summationIncomplete TetanusComplete Tetanus
85 TreppeStepping up of tension production to max level with repeat stimulation of the same fiber following relaxation phaseRepeated stimulations immediately after relaxation phase:stimulus frequency < 50/secondCauses a series of contractions with increasing tension
86 TreppeA stair-step increase in twitch tensionFigure 10–16a
87 Wave SummationRepeat stimulation before relaxation phase ends resulting in more tension production than max treppestimulus frequency > 50/secondTypical muscle contractionIncreasing tension or summation of twitchesFigure 10–16b
88 Incomplete TetanusRapid cycles of contraction and relaxation produces max tensionTwitches reach maximum tensionCardiac muscle incomplete tetanus Only to prevent seizureof heartFigure 10–16c
89 Complete Tetanus Relaxation eliminated, continuous contraction Fiber is in prolonged state of contractionProduces 4x more tension than maximum treppeQuick to fatigueMost Skeletal muscle complete tetanus whencontractingFigure 10–16d
90 Increased blood flow improves contraction. During treppe, why does tension in a muscle gradually increase even though the strength and frequency of the stimulus are constant?Increased blood flow improves contraction.Sarcomeres shorten with each contraction.Calcium ion concentration increases with successive stimuli.Generated heat improves contraction.
91 The factors that affect peak tension production during the contraction of an entire skeletal muscle, and the significance of the motor unit in this process.
92 Tension Produced by Whole Skeletal Muscles Depends on:Internal tension produced by sarcomeres- Not all the tension is transferred to the load, some of it is lost due to the elasticity of muscle tissuesExternal tension exerted by muscle fibers on elastic extracellular fibers- Tension applied to the load3. Total number of muscle fibers stimulated
93 Total Number of Muscle Fibers Stimulated Each skeletal muscle has thousands of fibers organized into motor unitsMotor units = all fibers controlled by a single motor neuronAxon branches to contact each fiberNumber of fibers in a motor unit depends on the functionFine control: 4/unit (e.g. eye muscles)Gross control: 2000/unit (e.g. leg muscles)Fibers from different units are intermingled in the muscle so that the activation of one unit will produce equal tension across the whole muscle
95 Recruitment (Multiple Motor Unit Summation) In a whole muscle or group of muscles, smooth motion and increasing tension is produced by slowly increasing size or number of motor units stimulatedRecruitment = order of activation of a motor unitSlower weaker units are activated firstStrong units are added to produce steady increases in tension
96 Contraction Skeletal Muscle During sustained contraction of a muscleSome units rest while others contract to avoid fatigueFor maximum tension, all units in complete tetanusLeads to rapid fatigueMuscle tone = maintaining shape/definition of the muscleSome units are always contractingExercise = Increase # of units contraction Increase in metabolic rate Increase in speed of recruitment (better tone)
97 KEY CONCEPTVoluntary muscle contractions involve sustained, tetanic contractions of skeletal muscle fibersForce is increased by increasing the number of stimulated motor units (recruitment)
99 Contraction Skeletal Muscle All contractions produce tension but not always movementIsotonic Contractions:- Muscle length changes resulting in movementIsometric Contractions- Tension is produced with no movement
101 Isometric Contraction Skeletal muscle develops tension, but is prevented from changing lengthNote: Iso = same, metric = measureFigure 10–18c, d
102 Return to Resting Length Expansion via:Elastic recoil after contractionThe pull of elastic elements (tendons and ligaments)Expands the sarcomeres to resting lengthOpposing muscle contractions- Reverse the direction of the original motionGravity- Opposes muscle contraction to return a muscle to its resting state
103 Can a skeletal muscle contract without shortening? Explain. Yes; isotonic contractions produce no movement.No; resistance is always less than force generated.Yes; concentric contractions are common.No; contraction implies movement.
104 The mechanisms by which muscle fibers obtain energy to power contractions.
105 Muscle Metabolism 1 fiber ~15 million thick filaments 1 thick filament ~ 2500 ATP/sec1 glucose (aerobic respiration) = 36 ATPEach fiber needs 1x1012 glucose/sec to contractATP unstable, muscles store respiration energy on creatine as Creatine Phosphate (CP)Creatine phosphokinase transfers P from CP at ADP when ATP is needed to reset myosin for next contractionEach cell as only ~20 sec of energy reserved
106 ATP and CP Adenosine triphosphate (ATP): Creatine phosphate (CP): the active energy moleculeCreatine phosphate (CP):the storage molecule for excess ATP energy in resting muscleEnergy recharges ADP to ATP:using the enzyme creatine phosphokinase (CPK)When CP is used up, other mechanisms generate ATP
107 Muscle Metabolism At Rest: Moderate Activity: Use glucose and fatty acids with O2 (from blood) aerobic respirationResulting ATP is used to CP reservesExcess glucose is stored as glycogenModerate Activity:CP used upGlucose and fatty acids with O2 (from blood) are used to generate ATP (aerobic respiration)
108 Muscle Metabolism High Activity: O2 not delivered adequately Glucose from glycogen reserves are used for ATP via fermentation (glycolysis only)Pyruvic acid is converted to lactic acidExcess lactic acid production leads to muscle cramps
109 ATP Generation Cells produce ATP in 2 ways: aerobic metabolism of fatty acids in the mitochondria (At rest and Moderate activity)Is the primary energy source of resting musclesBreaks down fatty acidsProduces 34 ATP molecules per glucose moleculeanaerobic glycolysis (fermentation) in the cytoplasm (High activity)Is the primary energy source for peak muscular activityProduces 2 ATP molecules per molecule of glucoseBreaks down glucose from glycogen stored in skeletal muscles
114 Factors that contribute to muscle fatigue, and the stages and mechanisms involved in muscle recovery.
115 Muscle FatigueWhen muscles can no longer perform a required activity (contraction), they are fatiguedDepletion of reserves- glycogen, ATP, CPDecreased pH due to:lactic acid productionDamage to sarcolemma and sarcoplasmic reticulumMuscle exhaustion and pain
116 To restore function, cell need: Intracellular energy reserves- Glycogen and CPGood Circulation- Nutrients in, wastes outNormal O2 levelsNormal pHLactic Acid Disposal
117 Normal pH Lactic Acid Disposal Lactic acid diffuses into the bloodFiltered out by the liverConverted back to glucose through the Cori CycleReturned to blood for use by cellsWhen O2 returnsRemaining lactic acid in the muscle is converted to glucose and used in aerobic cellular respiration
118 KEY CONCEPTSkeletal muscles at rest metabolize fatty acids and store glycogenDuring light activity, muscles generate ATP through aerobic breakdown of carbohydrates, lipids or amino acidsAt peak activity, energy is provided by anaerobic reactions that generate lactic acid as a byproduct
119 Muscle fibers and physical conditioning that relate to muscle performance.
120 Muscle Performance Power: Endurance: Power and endurance depend on: the maximum amount of tension producedEndurance:the amount of time an activity can be sustainedPower and endurance depend on:Types of muscle fibersFast Glycolytic Fibers (fast twitch)Slow Oxidative Fibers (slow twitch)Intermediate/Fast Oxidative FibersPhysical conditioningAerobic ExerciseResistance Exercise
121 Fiber TypesTypes of fibers in a muscle are genetically determined and mixedFast glycolytic Fibers (fast twitch)Myosin ATPase work quicklyAnaerobic ATP production: glycolysis onlyLarge diameter fibersMore myofilaments and glycogenFew mitochondriaFast to act, powerful, but quick to fatigueCatabolize glucose only
122 Fiber Types Slow Oxidative Fibers (slow twitch) Myosin ATPases work slowlySpecialized for aerobic respirationMany mitochondriaExtensive blood supplyMyoglobin (red pigment, binds oxygen)Smaller fibers for better diffusionSlow to contract, weaker tension, but resist fatigueCatabolize glucose, lipids, and amino acids
123 Fiber Types 3. Intermediate/Fast Oxidative Fibers Qualities of both fast glycolytic and slow oxidative fibersFast acting but perform aerobic respiration so to resist fatiguePhysical conditioning can convert some fast fibers into intermediate fibers for stamina
126 Muscles and Fiber Types White muscle:mostly fast fiberspale (e.g., chicken breast)Red muscle:mostly slow fibersdark (e.g., chicken legs)Most human muscles:mixed fiberspink
127 Physical Conditioning Aerobic Exercise:- Increase Capillary DensityIncrease Mitochondria and myoglobinBoth then:Increase efficiency of muscle metabolismIncrease strength and staminaDecrease fatigueResistance Exercise:Results in Hypertrophy:fibers increase in diameter but not numberIncrease glycogen, myofibrils, and myofilaments results in increase tension production
128 Physical Conditioning Growth Hormone (pituitary) and Testosterone (male sex hormone)Stimulate synthesis of contractile proteinsResults in Muscle EnlargementEpinephrineStimulates increase muscle metabolismResults in increase force of contractionWithout stimulation muscles will atrophyFibers shrink due to loss of myofilament proteinsLoss: up to ~5%/day
129 KEY CONCEPT What you don’t use, you loose Muscle tone indicates base activity in motor units of skeletal musclesMuscles become flaccid when inactive for days or weeksMuscle fibers break down proteins, become smaller and weakerWith prolonged inactivity, fibrous tissue may replace muscle fibers
130 Why would a sprinter experience muscle fatigue before a marathon runner would? Sprinters cannot utilize ATP for long periods of time.Sprinters’ muscles are most efficient aerobically.Sprinters’ muscles are most efficient anaerobically.Sprinters’ muscles are weaker.
131 Which activity would be more likely to create an oxygen debt: swimming laps or lifting weights? both A and Bneither A nor B
132 thick, glycogen-laden fibers Which type of muscle fibers would you expect to predominate in the large leg muscles of someone who excels at endurance activities, such as cycling or long-distance running?slow fibersfast fibersnonvascular fibersthick, glycogen-laden fibers
134 Cardiac Muscle TissueCardiac muscle is striated, found only in the heartFigure 10–22
135 Cardiac Muscle Tissue Forms the majority of heart tissue Cells = cardiocytesOne or two nucleiNo cell divisionLong branched cellsMyofibrils organized into sarcomeres (striated)No triads (no terminal cisternae)Transverse tubules encircle Z-linesAerobic Respiration OnlyMitochondria and myoglobin richGlycogen and lipid energy reservesIntercalated discs at cell junctions (gap junctions and desmosomes)allow transmission of action potentialslink myofibrils from on cardiocyte (cell) to the next
136 Coordination of Cardiocytes Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells
137 4 Functions of Cardiac Tissue Automaticity:contraction without neural stimulationAutomatically due to control by pacemaker cellsThese cells generate action potentials spontaneouslyPace and amount of contraction tension:Can be adjusted and controlled by the nervous systemExtended contraction time- Contraction is 10x longer than skeletal muscleOnly twitches, no complete tetanus- Prevention of wave summation and tetanic contractions by cell membranes
139 Structure of Smooth Muscle Nonstriated tissueFigure 10–23
140 Smooth Muscle Tissue Lines hollow organs Forms errector pili muscles Regulates blood flow and movement of materials in organsForms errector pili musclesUsually organized into two layerCircularLongitudinalSpindle shaped cellsSingle central nucleusCells capable of divisionNo myofibrils, sarcomeres, or T tubulesSER/ER throughout cytoplasmNo tendons
141 Smooth Muscle Tissue Thick filaments (myosin fibers) scattered Myosin fibers have more heads per thick filamentThin filaments are attached to dense bodies on desmin cytoskeleton (web)Adjacent cells attach at dense bodies with gap junctions (firm linkage and communication)Dense bodies transmit contractions from cell to cellContraction compresses the whole cell
142 Smooth Muscle in Body Systems Forms around other tissuesIn blood vessels:regulates blood pressure and flowIn reproductive and glandular systems:produces movementsIn digestive and urinary systems:forms sphinctersproduces contractionsIn integumentary system:arrector pili muscles cause goose bumps
143 Smooth Excitation-Contraction Different than striated muscle:no troponin so active sites on actin are always exposedEvents:Stimulation causes Ca2+ release from SRCa2+ binds calmondulin in the sarcoplasm- Calmondulin = CALcium MODULated proteINCalmondulin activates myosin light chain kinase, this complex phosphorylates myosinMLC Kinase converts ATP ADP to cock myosin headCross bridge form contraction, cells pull toward center
144 Smooth Excitation-Contraction Stimulation is by involuntary control from- Autonomic Nervous System- Hormones- Other Chemical FactorsSkeletal Muscle = Motor NeuronsCardiac Muscle = Automatically
145 Characteristics of Skeletal, Cardiac, and Smooth Muscle Table 10–4
146 Extracellular Ca2+ inhibits actin. Why are cardiac and smooth muscle contractions more affected by changes in extracellular Ca2+ than are skeletal muscle contractions?Extracellular Ca2+ inhibits actin.Crossbridges are formed extracellularly.Most calcium for contractions comes from SR stores.Most calcium for contractions comes from extracellular fluid.
147 Smooth muscle can contract over a wider range of resting lengths than skeletal muscle can. Why? Smooth muscle sarcomeres are longer.Myofilament arrangement is less organized in smooth muscle.Smooth muscle cells are shorter.Smooth muscle actin is longer.
148 Effects of Aging Skeletal Muscle fibers become thinner Decrease myofibrils, Decrease reserves =Decrease in strength and endurance andIncrease in fatigueDecrease cardiac and smooth muscle function =Decrease cardiovascular performanceIncrease fibrosis (CT):Skeletal muscle less elasticDecrease ability to repairDecrease satellite cellsIncrease scar formation
149 SUMMARY 3 types of muscle tissue: Functions of skeletal muscles cardiacsmoothFunctions of skeletal musclesStructure of skeletal muscle cells:endomysiumperimysiumepimysiumFunctional anatomy of skeletal muscle fiber:actin and myosin
150 SUMMARY Nervous control of skeletal muscle fibers: neuromuscular junctionsaction potentialsTension production in skeletal muscle fibers:twitch, treppe, tetanusTension production by skeletal muscles:motor units and contractionsSkeletal muscle activity and energy:ATP and CPaerobic and anaerobic energy
151 SUMMARY Skeletal muscle fatigue and recovery 3 types of skeletal muscle fibers:fast, slow, and intermediateSkeletal muscle performance:white and red musclesphysical conditioningStructures and functions of:cardiac muscle tissuesmooth muscle tissueAnnMarie Armenti, MS SCCC BIO 130