Chapter 7: The Muscular System

Chapter 7: The Muscular SystemSkeletalStriated actin/myosin org.voluntarySmoothnonstriatedinvoluntaryCardiac (heart)striatedInvoluntary (pacemaker cells)

Types of MuscleSkeletal: bonesSmooth: organs (respiratory, digestive, urinary, reproductive, blood vessels)Cardiac: heart muscleComposition:Skeletal muscle tissueConnective tissueNerves & Blood vesselsIntegrated within the connective tissue layers to deliver nutrients/stimulate cells (axons from CNS)Very active muscle cells need oxygen/nutrients and waste disposal

Functions:MovementPosture/PositionSoft tissue supportGuard entry/exitsMaintain body temp.Voluntary, controlledException of diaphragmSkeletal muscleSkeletal muscle is mainly composed of skeletal muscle tissue, but also contains connective tissue, nerves and blood vesselsThis is the muscle that is connected directly/indirectly to your bones, hence skeletal muscleFunctions: Contraction of muscles pull on tendons and move the bones, from simple to complex movementsMuscles are constantly contracting to maintain body posture, helps you sit uprightMuscles along the abdomen and floor of the pelvic cavity support the weight of visceral organs an protect internal tissues from injuryEncircle openings to digestive/urinary tracts. Voluntary control over swallowing, defecation and urination.Contractions release heat that maintains normal body temperature.Muscle fibers = multi-nucleated elongated cellsFascicle: bundle of muscle fibers

3 layers of connective tissue:Epimysium Epi = on, mys = muscleSurrounds entire musclePerimysiumPeri = aroundSurround fasciclesEndomysiumEndo = insideInside fascicleGross anatomyTendons form from coming together of collage fibers of all three layers. Or a broad sheet, aponeurosis. Tendons: muscle to boneAponeuroses: skeletal muscle to skeletal muscleTendon interwoven into periosteum of bone, strong connection to pull bones during contraction

Endomysium (surrounds muscle cell)Perimysium (surrounds fascicles)Epimysium (surrounds whole muscle)Sarcolemmasarkos = fleshlemma = huskCell membraneSarcoplasmCytoplasmTransverse tubulesT tubulesFunction in muscle contractionMyofibril: bundles of myofilaments

Microanatomy: Inside the muscle cellMuscle cell can be very large, as long as the muscle itselfOpenings along the surface of the muscle fiberT-tubules are integrated throughout the muscle fiber (cell), highway for electrical signals that function in contraction. Filled with extracellular fluid.Muscle cell contains hundreds to thousands of myofibrils (bundles of myofilaments-organized pattern of muscles)Contains myofilamentsThick and Thin Protein filamentsActin & Myosin proteinsActin (Thin)Myosin (Thick) Attached to sarcolemma at each end of cell (contraction)Figure 7-2 (p. 188)

MyofibrilENERGYMitochondria and glycogen granules scattered throughout the cell.Cellular respiration: sugar energyATP for contractions

Sarcoplasmic Reticulum (SR)Form of smooth ERTubular network around each myofibrilTerminal cisternae chambers on SR, sandwich T tubulesContain high [C] of calcium ions, which are released into sarcoplasm during contraction.MicroanatomySmallest functional unit of the muscle fiberOrganized, repeating units of myofilaments (thick/thin)~10,000 sarcomeres end to end in each myofibrilBanded (striated) appearance from myofilament organization, sarcomeres side by side Z linesBoundaries of sarcomere, one sarcomere from Z to ZM lineProtein that connects neighboring thick filamentsA band (dArk)Region of thick filaments (some thin in overlap, but more thick)I band (lIght)Region of thin filaments

sarcomereSliding filaments

Thin filaments: twisted strand of actinActinActive sites (reacts with myosin)Tropomyosin (cover active sites @ rest)Troponin (stability)Thick filamentsMyosinHead and tailHeads attach to actin during contractionCalcium is the KEY!

Thick and thin filamentsTroponin must move tropomyosin to expose active sites on actin for myosin to bind to. Calcium binds to troponin which changes shape and moves tropomyosin which exposes active sites. Terminal cisternae of Sarcoplasmic reticulum holds calcium source.Sliding filament theoryMyosin head (thick) binds to active sites on actin (thin)Needs calcium to bind to troponin, which moves tropomyosin and exposes active sites on actin

Sliding filaments and cross-bridgesSliding filament theoryWhen a muscle contracts:I band gets smallerZ lines move closerZones of overlap increaseWidth of A band stays the sameThin filaments slide toward centerThick filaments stay in placeCross-bridges: myosin heads connected to active sites on actinattach, pivot, detach, and return(Pulling a rope with one hand)

Sliding filaments and cross-bridgesIntercellular connection b/t nerves and muscle cellsMuscle fiber (cell)motor neuronAxons attach to perimysium and forms synaptic terminalSynaptic vesicles (ACh)Synaptic cleft Motor end plate (binding sites for ACh)Acetylcholinesterase (AChE)Breaks down ACh

Neuromuscular junctionNeuromuscular junction is where the nervous system communicates with the skeletal muscleSynaptic vesicles holding neurotransmitter, acetylcholine (chemical released by neurons for communication)ACh changes theSynaptic cleft (separate synaptic terminal and sarcolemma), portion of sarcolemma is called motor end plate (binding sites for ACh)Both contain enzyme acetlycholinesterase AChE (breaks down ACh) 1. Neuron 2. Sarcolemma (or motor end plate) 3. Synaptic Vesicle 4. Synaptic cleft 5. MitochondriaAction potential arrives at synaptic terminal3 & 4. ACh released from vesicles into the synaptic cleft5. ACh binds to receptors and Na ions rush into muscle cell7. AChE removes ACh and action potential moves through muscle cell Active site exposedMyosin Cross-bridgeMyosin pivots toward center (ADP + P)New ATP binds, mysin detachesMyosin re-primed when ATP ADP + P

SLIDING FILAMENT THEORY (Fig. 7-5)Calcium binds to troponin, moves tropomyosin, active site exposedprimed myosin attaches to active siteMyosin uses stored bond energy in power stroke and pivots toward centerNew ATP binds, myosin detachesATP splits to ADP + P, myosin primed for next cycleEnds when SR reabsorbs Ca2+ ions in the cisternae, will not reabsorb in consistent action potentialsTension: active force created when muscle fibers contract pullResistance: passive force that opposes movementCompression: opposite of tension, pushMuscles can only contract (shorten/create tension)We are not Mr. Fantastic!

Muscle mechanics

Stimulus-Contraction-Relaxation SequenceTwitch: single sequenceLatent Period: ~2msec, beings at stimulus, action potential propagates across sarcolemma, Calcium releasedContraction Phase: Cross bridges attach, maximum tension ~15msecRelaxation Phase: Cross bridges detach, calcium reabsorbed by SR, ~25msec

Muscle fiber stimulationSummationAddition of multiple twitches, from multiple stimuliIncomplete TetanusMaximum tension not reached (ex. Normal muscle movements)Complete TetanusMaximum tension, fast action potentials, no relaxation phase

Muscle fiber stimulationMotor unit: All muscle fibers controlled by a single motor neuronDepends on level on control neededEye: 2-3/nerveLeg: thousands/nerveMotor unitAtrophy: smaller and weaker muscles, not stimulated by nerves often

Muscle Tone: resting tension

Muscle tone & AtrophyIsotonic: tension rises, muscle length changesEqual tensionTension stabilized until relaxation

Types of contractionIsometric: length does not change, tension < resistance Equal measure(Ex. Pushing a door, picking up a car, sitting, standing)

Types of contractionRemember muscles ONLY contractReturn to resting stateElastic Forces (connective tissues)Contraction of opposing muscles (Biceps/Triceps)Gravity (Ex. Stand on one leg)Muscle elongationMuscle cells need energy from ATP. ATP is produced by cellular respiration, an aerobic process (needs oxygen)Lactic acid production during intense muscle activity, no time for oxygen to diffuse into muscle cellMuscle fatigue: caused by exhaustion of energy reserves or lactic acid buildupLactic acid lowers pH, muscles cannot function normallyRecovery period: muscle returns to preexertion levelsOxygen debt-breathing rate and depth increaseLactic acid glucoseHeat Loss: regulates body temperature (ex. Shivering)Muscle energeticsForce: maximum tension Endurance: duration of activityTwo types of skeletal muscle fibers:Fast (fast-twitch)0.01 sec stimulus responseLarge diameter, amount of myofibrils and glycogen reservesProne to fatigueSlow (slow-twitch)Half diameter of fast, 3x longer stimulus reactionLonger enduranceOxygen supply from capillariesOxygen storage in myoglobin (oxygen carrying red pigment)Oxygen use by more mitochondriaMuscle performanceFiber distribution:White muscles (white meat) composed of fast fibersRed muscles (dark meat) compose of slow fibersHumans: mixture of both fibers = pink appearance

Anaerobic endurance: energy from glycolysis and energy reservesEx. 50 yard dash/swim, pole vault, weight-liftingHypertrophy: muscle enlargement (body builders)Aerobic endurance: energy from mitochondrial activityEx. Jogging, distance swimmingCarboload before intense endurance activity

Physical conditioningEndurance: length of time on each energy sourceCARDIACSmall, single centrally placed nucleusOnly in the heartMyofibril pattern, branched, connect at intercalated discsInvoluntary (pacemaker cells)Longer contractionsAerobic metabolism (mitochondrial activity)

SMOOTHNo myofibrils, sarcomeres or striationsThick filaments dispersed and thin attached to sarcolemmaContraction over greater rangeInvoluntary (pacesetter cells)Cardiac & Smooth vs. skeletalTable 7-2AXIAL60% of muscles in the bodyPositions head and spinal columnRib cage movement for breathingIncludes muscles of:Head and neckSpineTrunkPelvic FloorAPPENDICULARStabilizes and moves appendagesIncludes muscles of:ShouldersUpper limbsPelvic GirdleLower LimbsMuscles to knowTable 7-3, PG. 207Origin and InsertionOrigin = the immovable end of the muscle

Insertion = the movable end of the muscle

**when a muscle contracts the insertion is moved toward the originThe biceps brachii has two origins (or two heads).AXIALFrontalisTemporalisOccipitalisMasseterSternocleidomastoidExternal obliqueRectus abdominis

Muscles to knowFig. 7-11, pg. 205-206APPENDICULARTrapeziusDeltoidPectoralis majorLatissimus dorsiBiceps brachiiTriceps brachiiGluteus medius/maximus

Muscles to knowFig. 7-11, pg. 205-206Adductor magnus/longusSartoriusRectus femorisBiceps femorisGastrocnemiusFibularisSoleusTibialis anteriorCalcaneal tendon (Achilles)Effects of aging:Muscle fiber diameter decreasesDecrease in number of myofibrilsStrength and endurance decreaseRapid fatigue (dec. cardiovascular performance)Muscle elasticity decreasesFibrosis: increase in fibrous connective tissue, makes muscles less flexibleExercise tolerance decreasesHeat loss is limited (65+ reduced thermoregulation)Rapid fatigueRecovery and repair abilities decreaseRepair limited, scar tissue forms

Aging and the muscular systemCardiovascularoxygen delivery and removal of waste and heatRespiratoryrate and depth of breathing paced with exercise, oxygen and carbon dioxide exchangeIntegumentaryblood vessel dilation and sweat glands work to remove excess heat from muscle activityNervous & Endocrinecontrol heart rate, respiratory rate, and sweat gland activityIntegration with other systemsBlood vessels in the skin dilate, allowing heat to transfer from the body out to the environment

10 Systems TotalSo far.IntegumentarySkeletalMuscular

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