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MUSCLE TISSUESDr. Antonio C. Villarivera Jr. MD1REMINDER This concept lecture is designed to guide the student in understanding the topic. IT IS NOT INTENDED TO BE A "STAND ALONE" REVIEW MATERIAL. Thus any information written or shown in this presentation SHOULD BE SUPPLEMENTED by readings from established reference materials.

2Objectives Discuss the structural and functional characteristics of muscle tissueCompare and differentiate skeletal, cardiac and smooth musclesDiscuss the chemistry and events in the contraction and relaxation of musclesDiscuss other muscle molecules- actinin, nebulin, ryanodine receptor;desmin; dystrophin, titin; contractile and regulatory proteins;caveolin3

4Muscle TissueAbout 40 per cent of the body is skeletal muscleAnother 10 per cent is smooth and cardiac muscle5

Muscle TissuePrimary function is for contractilityResponsible for locomotion, and movement of the various parts of the body3 types:Skeletal muscleSmooth muscleCardiac muscle6

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SMOOTH CARDIAC SKELETAL8Skeletal MuscleLocated attached to the boneLong & cylindrical in shapeMultinucleated located at the peripheryFibers have striationsUnder voluntary controlBasic function is for movement

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Smooth MuscleLocated along the walls of hollow organs, blood vessels and glandsSpindle shaped fibersHave a single centrally located nucleus No striations and under involuntary controlFunctions in compressing hollow organs, ducts & tubes

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Cardiac MuscleForms the musculature of the heartFibers are cylindrical in shape but with branchesUsually have a single centrally located nucleus Fibers have striations but are under involuntary controlFunctions in heart contraction to propel blood throughout the body

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Physiologic Anatomy of a Skeletal Muscle15Skeletal Muscle FiberComposed of numerous fibers ranging from 10 to 80um in diameterEach fiber is made up of successively smaller subunitsEach fiber extends the entire length of the muscleExcept for about 2%, each fiber is usually innervated by only one nerve ending, located near the middle of the fiber16

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Skeletal Muscle Fiber Sarcolemma-cell membrane of the muscle fiberSarcoplasmCytoplasm of the muscle cell and fibers which is acidophilic in stainingSarcosomeGranules in the cytoplasm18

Skeletal Muscle Fiber MyofibrilsFine thread like structures in the sarcoplasm which are responsible for muscle contractionSarcoplasmic reticulumThe endoplasmic reticulum in the muscle cell; contains Ca ions that are needed in the process of contraction19

Skeletal Muscle Fiber SarcomereStructural and functional unit of the muscle cellEndomysiumLoose collagenous tissue covering the individual muscle fiberPerimysiumLoose collagenous tissue covering the bundles of fascicles of muscle tissueEpimysiumDense collagenous tissue covering the whole or entire muscle itself

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Microscopic Appearance 22Microscopic AppearanceAppears to have cross striations on electron microscopy (skeletal & cardiac muscle)Due to overlapping of light & dark bandsDark bands- made up of thick filaments made up of the protein myosinLight bands- thin filaments of actinThick bands appear dark ( A band); the thin appear light (I band)23Microscopic AppearanceZ line- a narrow dark staining band found in the central region of the I bandH band or H zone- darker section of the A band; where myosin filaments are thickest and where there are no cross bridgesSarcomere- area between 2 adjacent Z lines; where actual contraction occurs at the molecular level2425

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Physiologic of Muscle Contraction 29Physiology of Muscle ContractionSurrounding the sarcolemma are ionsNa+ higher concentration outside muscle cellK+ higher concentration inside muscle cellResting potential - charge outside is positive and the inside is negative

30Physiology of Muscle ContractionAs a nerve impulse reaches the neuromuscular junction, it releases a neurotransmitter (acetylcholine)Acetylcholine produces an electrical potential that causes Na+ ions to rush inside the cell The influx of Na causes the inside of the cell to go from being negative to positive ACTION POTENTIAL is produced MUSCLE CONTRACTION occurs

31Physiology of Muscle ContractionK+ moves outside cell attempting to balanceThe electrical potential travels in all directions along the muscle cell (5 meters per second)The action potential travels all through out the muscle cell via the T-tubules

32Physiology of Muscle ContractionThe action potential reaches the sarcoplasmic reticulum and Ca is releasedCa negates the inhibitory effect of troponin and tropomyosin causing contractionWhen the Na-K pump restores the resting membrane potential, the contraction process ceases33Chemical InteractionsThe shortening of the contractile elements in the muscle is brought about by the pulling of the actin flaments over the myosin filamentsThe width of the A band remains the same while the Z lines move closer togetherWhen contraction stops, the actin filaments get released from the myosin and the Z lines move farther apart34The shortening of the contractile elements in the muscle is brought about by the pulling of the actin filaments over the myosin filamentsThe width of the A band remains the same while the Z lines move closer together

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36Chemical InteractionsWhole complex process occurs in 1/40 of a second37Smooth Muscle38Smooth MuscleComposed of far smaller fibersusually 1 to 5 um in diameter and only 20 to 500 um in length2 major types:Multi unit smooth muscleUnitary smooth muscle39

Multi Unit Smooth Muscle Composed of discrete, separate smooth muscle fibers Each fiber can contract independentlyOften innervated by a single nerve ending, as occurs for skeletal muscleThe outer surface is covered by a thin layer of basement membrane that helps insulate & separate the fibers from one anotherEx: arector pili, ciliary eye muscle

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Unitary Smooth MuscleFibers usually are arranged in sheets or bundlesTheir cell membranes are adherent at multiple points; so the force generated can be transmitted to the nextCell membranes are joined by gap junctions (ions & action potentials can flow freely from one muscle cell to the next)Ex: segments of the GIT, ureters41

Contractile Mechanism of the Smooth Muscle42Physical Basis for Smooth Muscle ContractionMechanism of contraction is different from skeletal muscleFibers made up of actin & myosin filaments but no troponinArrangement of myofilaments is different thus no striationsActin filaments are attached to dense bodies that are likewise attached to the cell membraneMyosin filaments are interspersed with the actin filaments

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Physical Basis for Smooth Muscle ContractionActin filaments radiate from two dense bodies; the ends overlap a myosin filament located midway between the dense bodiesMyosin filaments have sidepolar cross-bridges (allows smooth muscle cells to contract as much as 80 per cent of their length)Dense bodies of smooth muscle serve the same role as the Z discs in skeletal muscle44

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Isotonic muscle contractionthe muscle maintains the same tension as it shortensactivities that involve isotonic contractions include walking, running or lifting a light objectisotonic contractions come in two varieties: concentric and eccentricconcentric contraction (muscle shortens when its tension is greater than the force opposing it, such as your biceps does when performing an arm curl)eccentric contraction ( the force is greater than the muscle tension, causing the muscle to elongate; this happens when going down stairs or sitting down in a chair, as the effects of gravity add to the opposing force)46Isometric muscle contractionmeans same length, and in contractions of this variety, the muscle does not shorten and its tension never exceeds the opposing forceinclude holding a weight in place above the ground or pushing against a stationary object.while the entire muscle does not change length during an isometric contraction, the individual muscle fibers will shortenisometric exercises can help to strengthen a muscle47Contraction of muscle by summationSummationthe increasing rate of motor unit recruitment contractions to produce variations in the intensity, force, and duration of muscle contractions

48Tetanization the induction of tetanic convulsions or muscular spasmssustained muscular contractionsMuscle fatigue muscle loses its ability to contract as a result of overactivityusually a period after stimulation during which the muscle is unresponsive to a second stimulus

49End of Lecture Thank You50