GAP Muscle System Guided Notes PDF

GAP - Muscles and Muscle Tissue Nearly half of body’s mass Can transform chemical energy (ATP) into directed mechanical energy, which is capable of exerting force To investigate muscle, we look at: – Types of muscle tissue, Characteristics of muscle tissue, and Muscle functions Muscular Syst...

GAP - Muscles and Muscle Tissue Nearly half of body’s mass Can transform chemical energy (ATP) into directed mechanical energy, which is capable of exerting force To investigate muscle, we look at: – Types of muscle tissue, Characteristics of muscle tissue, and Muscle functions Muscular System – This system allows the movement of organs and of the body. – Muscles are very vascular and well innervated. – Characteristics o Excitable/Irritable:ability to relieve respond to stimuli o Contractible: to shorten when stimulated Ability Ability to be o Extensibility: stretched Ability to recoilto vesting o Elastic: length Types of Muscle Tissue Terminologies: _________, _________, and ____________ Sarco are prefixes for muscle MYpopasm exsurcoplasmmuscle MYS Only ___________ Skeletal and _______________muscle smooth cells are elongated and referred to as muscle fibers REVIEW - Describe the following muscle tissue characteristics: Skeletal muscle skeletal musclesorgans are attached to bonesandskin Skeletalmuscle tissue ispackaged into Skeletal muscle fibersare longest of all muscle have striations stripes voluntary striated andvoluntary key words skeletal contractrapidly tireeasilypowerful Cardiac muscle in heart Cardiac.MY 1 psueulkisofhYart hd key words cardiacstriatedinvoluntary Striated nervoussystemstimulates ftp.Itowsthadyrate 19991 81 Intercalated disks Smooth muscle hollow organs Smooth muscletissuefound in wallsof ex stomach andairways urinarybladder Not striated tYntract lnvo.ly on itsown woutsignal from brainnervoussystem Muscle Functions Four important functions: 1.Produce movementresponsiblefor all locomotionmanipulation moving 2.Maintain Posture bodyposition 3. Stabilize joints 4. Generateheat asthey contract Additional functions: organsform valuescontrolpupilsizecause goosebumps Protect control ha Perinethrough Skeletal Muscle Anatomy Skeletal muscle is an organ made up of different tissues with three features: nerve and blood supply, connective tissue sheaths, and attachments Nerve and Blood Supply - eachmusclehas a nervearteryandveins needs.cn i8uslydMcontrotiedosiaeietatrimU'screhes nervessupplyingeveryfiber tocontrolactivity waste products need tobe removed quickly Attachments Muscles span joints and attach to bones Muscles attach to bone in at least two places – insertion -moveableattachmentpoint – origin - immovable Attachments can be direct or indirect – Direct -fleshy muscleepimysium fusedto periosteum ofbone or perichondrium of cartilage – Indirect -CT wrappingsextend beyondmuscleasropeliketendonor sheetlike aponeurosis Types of Muscles: Prime mover (agonist) -Mainmusclefora specific movement Antagonist -worksopposite of Primemover Synergist -HelpermusclehelpsP.Mmakesmovementsmoother Fixator - joint type of synergistalsostabilizes a Connective Tissue Sheaths Each skeletal muscle, as well as each muscle fiber, is covered in connective tissue o Support cells and reinforces the whole muscle Sheaths from external to internal: o Epimysium Denseirregular C.T surroundingmusclemayblendwfascia oPerimysium Fibrous CT surrounding fasciclesclusterof musclecells oEndomysium fineareolarCT SurroundingeachmuscleEphyused  ***KNOW FIGURES Below!*** Epimysium Bone tendon vessel blood iii iii t.is µ MIST Fascicle Perimysium Sarcolemma redo mitochondrion Myotibril liganta nucleus Banka I undit mothiumgoesw Muscle Fiber Microanatomy and Sliding Filament Model Skeletal muscle fibers are long, cylindrical cells that contain multiple nuclei Sarcolemma -Musclefiberplasmamembrane Sarcoplasm -Musclefibercytoplasm fluidwithincell organelle Contains many ___________________ glycosomes for glycogen storage, as well as _________________ myoglobin for O2 storage Modified organelles: packeddifferentamounts in diff canmakemore80 ofmuscle muscles 1. Myofibrils - thmtttmfeanMsely yluome.im sacromere's.ly striations – A bands - darklines H zone -lighterregionwithintheAband – M line - proteinfound in centerof A bandanchors myosin protein timing – I bands - my Z disc (line) - Zigzagline ofprotein in centerof 1 bandanchors actinprotein  withinmyotibril 2. Sarcomere - LABEL a Sarcomere Below: Individual sarcomeresalignend toend along myotibriltrain boxcars smallest contractileunit of musclefiber two discs ftp.tnktween adisc areataflangesize Zdisc filament I band _thick myosin typed Aabad LaMono myosin One sarcomere 3. Myofilaments arrangement of actin myosinwithin sarcomere – Actin myofilaments: thin filament band In 1 bandandpart of A Anchored to Z disc – Myosin myofilaments: thick surrounded by hexagonal filaments thick filaments an Extend through A band arrangement Connected at M line Molecular composition of myofilaments – Thick filaments: composed of protein ______________ that contains two heavy and four light Myosin polypeptide chains Heavy chains intertwine to form myosin tail Light chains form myosin globular head whentheyattach – During contraction, heads link thick and thin filaments together, forming cross bridges Myosins are offset from each other, resulting in staggered array of heads at different points along thick filament Label the sarcomere below: Thin filaments Actin Activesites formyosin head attachment during contraction Troponin Tropomyosin bound proteins egulatory whethermyosin Control 0 ActinActinfor contraction abindto 0Eur  Hopomyosin fins Sarcoplasmic Reticulum and T Tubules Sarcoplasmic reticulum - Smoothe ER tubules surrounding fibril eachmyo Emmadcisterhhf.pro ciossEianieis atta I bandjunction T tubules - transverse deepintocellinterior hehad In gentymma Surfaceareas reachdeepintointerior Allowelectricalnervetransmissions to ofeachmusclefiber Triad - terminalcisterna tubuleandterminal cisterna onotherside Areaformed by that protrudeinto intermembrane space TtubuleCurtailingEphenneakenauphens that protrudeinto intermembrane space haveintegral SRcistmahamms.am control openings of catchannels in SR cisterns -Label the TRIAD below: f1yggff TfPwY Triad myotibrif c Contracts p Sliding Filament Model of Contraction ÉEETEN Cellmembrane sarcolemma Contraction: o Shortening occurs when tension generated by cross bridges on thin filaments exceeds forces opposing shortening o Contraction ends when cross bridges become inactive o In the relaxed state, thin and thick filaments overlap only slightly at ends of A band Sliding filament model of contraction - Describe what this theory states: During contraction thin filaments slide past thick filamentscausing actin and myosin to overlap more Actin Myosin do not change length justoverlap more  When nervous system stimulates muscle fiber, myosin heads are allowed to bind to actin, forming cross bridges, which cause sliding (contraction) process to begin Cross bridge attachments form and break several times, each time pulling thin filaments a little closer toward center of sarcomere in a ratcheting action – Causes shortening of muscle fiber What happens to each of the following structures during contraction? o Z discs -pulled toward M lineinwardcomecloser together o I bands -shortened o myosin H zones - disappear just o A bands -Moveclosertoeachother multiple sarcomere Muscle Fiber Contraction Four steps must occur for skeletal muscle to contract: 1.Nerve Stimulation sarcolemma 2.ActinPotential an electrical currentmust begenerated in 3.Actin Potential must be propagated along sarcolemma 4. Intracellular I Ca't levels must briefly Steps 1 and 2 occur at____________________________________ neuromuscular junction excitation contraction Steps 3 and 4 link electrical signals to contraction, so referred to as ________________________ coupling The Nerve Stimulus and Events at the Neuromuscular Junction Skeletal muscles are stimulated by - Somatic motorneurons frombrain tomuscle cells in body Axons (long, threadlike extensions of motor neurons) travel from central nervous system to skeletal muscle o Each axon divides into many branches as it enters muscle o Axon branches end on muscle fiber, forming _______________________ neuromuscular junction or endplant ________________ motor – Each muscle fiber has one neuromuscular junction with one motor neuron o Axon terminal (end of axon) and muscle fiber are separated by gel-filled space called __________________ cleft synaptic Stored within axon terminals are membrane-bound synaptic vesicles – Synaptic vesicles contain neurotransmitter _____________________________ acetylcholine ACh Infoldings of sarcolemma, called junctional folds, contain millions of ACh receptors NMJ consists of axon terminals, synaptic cleft, and junctional folds DRAW a Neuromuscular junction below: item Events at the neuromuscular junction – Nerve impulse arrives at axon terminal, causing ACh to be released into synaptic cleft – ACh diffuses across cleft and binds with receptors on sarcolemma – ACh binding leads to electrical events that ultimately generate an action potential through muscle fiber acetylcholinesterase – ACh is quickly broken down by enzyme _______________________, which stops contractions Clinical – Homeostatic Imbalance Many toxins, drugs, and diseases interfere with events at the neuromuscular junction – Example: Myasthenia gravis - difficulty controlling contracting muscles drooping upper eyelids difficult swallowing talking thick not _generalized muscleweakness enough receptors ACh Timaru receptors  Generation of an Action Potential Across the Sarcolemma Resting sarcolemma is polarized, meaning a voltage exists across membrane – Inside of cell is __________________compared negative to outside Action potential is caused by changes in electrical charges Occurs in three steps 1. End plate potential neuromuscular junction 2. Depolarization 3. Repolarization 1. End plate potential – ACh released from motor neuron binds to ACh receptors on sarcolemma ligand – Causes chemically gated ion channels (ligands) on sarcolemma to open – _______ diffuses into muscle fiber Some _____ diffuses outward, but not much – Because ______ Nat diffuses in, interior of sarcolemma becomes ______ less negative (___________ more positive) – Results in local depolarization called ___________________ end potential plate 2. Depolarization: generation and propagation of an action potential (AP) – If end plate potential causes enough change in membrane voltage it will reach a OncestartsNat critical level called __________________. threshold What type of gated ion channel will open? doesn't stop going o Na channelmarane voltage gated into cell Nat – Large influx of ___________ through channels into cell triggers AP that is membrane unstoppable and will lead to muscle fiber contraction – AP spreads across sarcolemma from one _____________________ voltagegated Nat channel to next one in adjacent areas, causing that area to depolarize 3. Repolarization: restoration of resting conditions startsquicklyafter – _______ kt Nat voltage-gated channels close, and voltage-gated _________ channels open kt – ______ efflux out of cell rapidly brings cell back to initial resting membrane voltage It goesout of cell concentration – ________________period: muscle fiber cannot be stimulated for a specific high low Refactory amount of time, until repolarization is complete Totalitum chargewill become more negative resting Nat kt pump 14g smfh – Ionic conditions of resting state are restored by __________________________ ▪ Na+ that came into the cell is pumped back out, and K+ that flowed outside is normal pumped back into the cell. Draw this mechanism below: 2kt in 3 out  Excitation-Contraction (E-C) Coupling Excitation-contraction (E-C) coupling: What is this? events that transmit AP along sarcolemma exitation are coupled to sliding of myo filaments contraction AP is propagated along sarcolemma and down into T tubules, where voltage-sensitive proteins in tubules stimulate ________ release from sarcoplasmic reticulum dentin E – ________ release leads to contraction o AP is brief and ends before contraction is seen Channels Involved in Initiating Muscle Contraction Nerve impulse travels down axon of motor neuron When impulse reaches axon terminal, ______________________________ channels open, and voltage gated ______ enters axon terminal _______ influx causes synaptic vesicle to exocytose Ach into synaptic cleft o REVIEW - What is exocytosis? Nat kt channels to open ACh binds to receptors on sarcolemma, causing chemically gated _________ and initiate an end plate potential When threshold is reached, voltage-gated _____ channels open, initiating an AP TEngen  Muscle Fiber Contraction: Cross Bridge Cycling At low intracellular Ca2+ concentration: Tropomyosin blocksactivesites on actin Myosin headscannotattach to actin Musclefiberremainsrelaxed Voltage-sensitive proteins in T tubules change shape, causing SR to release Ca2+ to cytosol At higher intracellular Ca2+ concentrations: Ca't binds to troponin Troponin changesshapeandmovestropomyosinawayfrom myosinbindingsites Myosin heads isthen allowed to bind to actinforming crossbridge Cycling is initiated, causing sarcomere shortening and muscle contraction When nervous stimulation ceases, _______ is pumped back into SR, and contraction ends Ca Four steps of the cross bridge cycle 1. Cross ______________________: BridgeFormation high-energy myosin head attaches to actin thin filament active site 2. ______________________: myosin head pivots and pulls thin filament toward M line Working Power Stroke 3. Cross ______________________: Bridge detachment ATP attaches to myosin head, causing cross bridge to detach 4. Cocking ______________________: energy from hydrolysis of ATP “cocks” myosin head into of Myosin Head high-energy state This energy will be used for power stroke in next cross bridge cycle NeedCa ATP and Clinical – Homeostatic Imbalance Rigor mortis - 3 musclesbegin to stiffen 4 highafterdeath tisnodelflhafho.in Intracellular calciumlevels increase because ATP be pumped into SR longer being synthesizedso catcannot Results in Crossbridgeformation releasesactin Muscles stay contracted untilproteinsbreak downmyosin 9.5 Whole Muscle Contraction – Same principles apply to contraction of both single fibers and whole muscles Contraction produces _____________________, muscle tension the force exerted on load or object to be moved Contraction may/may not shorten muscle: – isometric contraction - shorteningmuscletensionincreases butdoes not exceed load no too heavycan't lift – isotonic contraction - muscleshortens because muscle tension exceeds load can lift Force and duration of contraction vary in response to stimuli of different frequencies and intensities Each muscle is served by at least one motor nerve brain tomusitetells to contract – Motor nerves contains axons of up to hundreds of motor neurons – Axons branch into terminals, each of which forms NMJ with single muscle fiber 1 Motor unit is the nerve-muscle functional unit neuromuscularjunction The Motor Unit Describe what a Motor unit is -Motor neuron muscle fibers supplied motor neuron and allthe muscle fibers it connects and sends signals to Smaller fiber number greaterthefinecontrol Eniggya p Muscle fibers from a motor unit are spread throughout the whole muscle, so stimulation of a single motor unit causes only weak contraction of entire muscle  The Muscle Twitch Muscle twitch -Simplest Contraction resulting from a muscle fiber's response to a Single action potential from a motor neuron veryquick Single ActionPotential tosingle cell Twitch can be observed and recorded as a ____________________ – Tracing -line recording contraction activity 409AM Three phases of muscle twitch – latent period - events of excitation contractioncoupling faster– contraction period - crossbridge formation slower– relaxation period - Cat reentry into SR tension goes back to zero Muscle contracts faster than it relaxes Differences in strength and duration of twitches are due to variations in metabolic properties and enzymes between muscles – Example? contraction arerapid and briefwhereas largerfleshy muscles calf muscles eye muscle Contract more slowly hold it longer Graded Muscle Responses Normal muscle contraction is relatively smooth, and strength varies with needs – A muscle twitch is seen only in lab setting or with neuromuscular problems, but not in normal muscle Graded muscle responses vary strength of contraction for different demands – Required for proper control of skeletal movement Responses are graded by: – Changing frequency of stimulation Vary strength time – Changing strength of stimulation more than 1 stimuli her  Muscle response to changes in stimulus frequency – Single stimulus results in single contractile response (i.e., muscle twitch) – Wave (temporal) summation results if two stimuli are received by a muscle in rapid succession Multiple Muscle fibers do not have time to completely relax between stimuli, so twitches increase in Signals are force with each stimulus sent Additional Ca2+ that is released with second stimulus stimulates more shortening Produces smooth, continuous contractions that add up (summation) Smart Further increase in stimulus frequency causes muscle to progress to sustained, quivering contraction referred to as _____________________________ unfused incomplete tetanus muscle quivers because – If stimulus frequency increases, muscle tension reaches maximum muscle is getting tired Referred to as __________________________ fused complete tetanus because contractions “fuse” into one smooth sustained contraction plateau and 1k together Prolonged muscle contractions lead to muscle __________________ fatigue -Muscle response to changes in stimulus strength – Recruitment (or multiple motor unit summation): Stimulus is sent tomore musclefibersleading to more percise control how many motorUnitsare used – Types of stimulus involved in recruitment: o Subthreshold stimulus: stimulus is not strong enough so no contraction o Threshold stimulus: contracformulus is strong enough to cause first observable o Maximal stimulus:strongest stimulus that increases maximum contractile force Allmotor units have been recruited – Recruitment works on size principle- Motor unitswith smallest fibersare recruited first move up size gradient motor units wlarger fibers are recruited as stimulusintensity increases motor units are activated onlyformost powerful contractions Largest othersrest prevent fatigue Motorunits muscleusually contract asynchronously some contractwhile in Muscle Tone- Constantslightly contracted state of all muscles Due to spinalreflexes activated in groupsof motor units are alternatively response to inputfrom stretch receptors in muscles keep muscles firmhealthready to respond  mp by Isotonic and Isometric Contractions Isotonic contractions:musclechanges lengthmovesload Concentric contractions:muscle shortens doeswork contractshorten Eccentric contractions:muscle lengthens generatesforce ExtendT longer Isometric contractions:load is greaterthanmaximum muscletension Muscle doesn't shorten or lengthen TOO HEAVY Energy for Contraction and ATP Providing Energy for Contraction -ATP supplies the energy needed for the muscle fiber to: move detach cross bridges _IT 8 bands intocell afterexcitationcontraction coupling of ATPdepletes in 4 6 seconds Availablestores ATP is only source of energyfor contractile activitiesneeds to regenerate quickly ATP is regenerated quickly by three mechanisms: Direct phosphorylation of ADP by creatine phosphate (CP) – Creatine phosphate is a unique molecule located in muscle fibers that donates a phosphate to ADP to instantly form ATP Creatine kinase is enzyme that carries out transfer of phosphate Muscle fibers have enough ATP and CP reserves to power cell for about _________seconds 15 -What is the reaction for direct phosphorylation? How many ATP are produced from each ATP? Creatine phosphate ADP creatine ATP ICP 1 ATP Anaerobic pathway: glycolysis and lactic acid formation – ATP can also be generated by breaking down and using energy stored in glucose Glycolysis: first step in glucose breakdown – Does not require ________________ faster ZATP – Glucose is broken Oxygen into _____ pyruvic acid little molecules 1 glucose 2 ATPs are generated for each glucose broken down – _____ ▪ Low oxygen levels prevent pyruvic acid from entering aerobic respiration phase – Normally, pyruvic acid enters mitochondria to start aerobic respiration phase; however, at high intensity activity, oxygen is not available Why? muscles compress blood vessels Bulging impairing oxygen delivery – In the absence of oxygen, referred to as ____________________, anaerobic glycosis pyruvic acid is lactic Acid converted to _________________ ▪ What happens to remove this substance from the muscles? diffuses intobloodstreamUsed as fuel by liverkidneysandheart Converted back into pyruvicacidor glucose byas aerobic respiration, but produces ATP liver – Anaerobic respiration yields only 5% as much ATP 2½ times faster  Aerobic respiration ideal – Produces 95% of ATP during rest and light-to-moderate exercise ________________ than anaerobic pathway slower – Consists of series of chemical reactions that occur in ______________________ and mitochondria require _________________ oxygen Breaks glucose into CO2, H2O, and large amount ATP (______can be produced) 3236 – Fuels used include glucose from glycogen stored in muscle fiber, then bloodborne glucose, and free fatty acids ______________________ Acids are main fuel after 30 minutes of exercise Fatty Energy systems used during sports – Aerobic endurance - Light to moderate activity can continue for hours – Anaerobic threshold - Pointat which muscle metabolism converts to anaerobicpathway Muscle Fatigue: Physiological inability to contract despite continued stimulation Occurs when ionicimbalance levels of ktCartD mayalsodamageSRinterfereswcastregulation release Prolonged excersise Lack of ATPis rarely areason forfatigueexcept Severly stressedmuscks in Excess Postexercise Oxygen Consumption For a muscle to return to its pre-exercise state: Oxygenreservesare replenished Lactic acid is reconverted to pyruvicacid Glycogen stores are replaced ATPand creatinephosphatereservesare resynthesized All replenishing steps require extra oxygen, so this is referred to as excess postexercise oxygen consumption (EPOC) – Formerly referred to as “________________” Oxygendebt Factors of Muscle Contraction Force of Muscle Contractions Force of contraction depends on number of cross bridges attached, which is affected by four factors: o Number of muscle fibers stimulated (recruitment): more motorunits recruitedthe greaterthe force o Relative size of fibers: the bulkier the musclethe moretension it can develop musclecellscanincrease in size wrregexercise o Frequency of stimulation: higher the frequencythegreaterthe force Stimuli are addedtogether o Degree of muscle stretch: muscle fibers withsarcomeresthat and 80120 their normal resting lengthgeneratemoreforce if sarcomere is lessthan 80 resting lengthfilamuts overlap toomuchforce decreases  over 120 resting lengthdon'toverlapenoughlessforce Velocity and Duration of Contraction How fast a muscle contracts and how long it can stay contracted is influenced by what 3 things? Muscle fiber type Load Recruitment Muscle fiber type – Classified according to two characteristics slow 1. Speed of contraction – _________or fast ________fibers according to: o Speed at which myosin ATPases split ATP o Pattern of electrical activity of motor neurons recieve signals 2. Metabolic pathways used for ATP synthesis o __________________ Oxidative fibers: use aerobic pathways o __________________ fibers: use anaerobic glycolysis Glycolytic – Based on these two criteria, skeletal muscle fibers can be classified into three types: Slow oxidative fibers, fast oxidative fibers, or fast glycolytic fibers – Most muscles contain mixture of fiber types, resulting in a range of contractile speed and fatigue resistance All fibers in one motor unit are the same type Genetics dictate individual’s percentage of each – Different muscle types are better suited for different jobs Slow oxidative (red) fibers: 1.9jiteitnfiaadura.mn Entities atslown respiration ex maintaining posture small to fractions fatigue Fast oxidative (pink) fibers: mediumintensity activities Milportant Fast glycolytic (white) fibers: Shorttermintense or powerful movements sprinterspowerlifters lotsof force exittertintilisight aatiiue.cat Adaptation to Exercise Aerobic (endurance) exercise, such as jogging, swimming, biking leads to: increased Muscle capillaries number of mitochondria myoglobin synthesis Results in greater endurancestrengthandresistance to fatigue May convert fast glycolyticfibers intofastoxidative fibers Resistance exercise (typically anaerobic), such as weight lifting or isometric exercises, leads to: muscle hypotrophy increase in fiber size filamentsglycogenstoresandconnective tissue increased mitochondriamyo increased muscle strength andsize Clinical – Homeostatic Imbalance Muscles must be active to remain healthy Disuse atrophy - degeneration andloss of mass loss of neural stimulation beginMambo tinned fy o Muscle strength can decline 5% per day o Paralyzed muscles may atrophy to one-fourth initial size o Fibrous connective tissue replaces lost muscle tissue ▪ Rehabilitation is impossible at this point 9.9 Smooth Muscle Where is smooth muscle found? muscle found insideholloworgans exceptheartcardiac Microscopic Structure – Describe what smooth muscle cells look like - noepimysi.amperimysium Spinleshaped thinshortuninucleatenostriations y Lacks connective tissue sheaths - Contains __________________ only mammam All but smallest blood vessels contain smooth muscle organized into two layers of opposing sheets of fibers _________________layer: fibers run parallel to long axis of organ samewayas organ – Longitudinal Contraction causes - organ to shorten – Circular _________________layer: fibers run around circumference of organ Contraction causes - Organ to constrict narrow lumencenterhollowregion o Allows peristalsis - contractions relaxations of layers mixsqueeze substancesthrough lumen of hollow orgatternating No ____________________________, neuromuscular junction as in skeletal muscle o Instead, _________________ nerve fibers innervate smooth muscle o Containautatisfies ____________________ (bulbous swellings) of nerve fibers o _________________ store and release neurotransmitters into a wide synaptic cleft referred to Varicosity as a _____________________ fuse junction Smooth muscle does not contain_____________________________________________________ garcomeres myo fibrilsor T tubules SR is less developed than in skeletal muscle – SR does store intracellular Ca2+, but most calcium used for contraction has extracellular origins – Sarcolemma contains pouchlike infoldings called __________________ Caveolae o ________________contain Caveolae numerous Ca2+ channels that open to allow rapid influx of extracellular Ca2+ cast goes through careolae Pouches  Smooth muscle also differs from skeletal muscle in following ways: – Thick filaments are fewer and have myosin heads along entire length- Ratio of thickto thin filaments 113 is much lowerthan skeletal muscle 1 2 Thick filaments have heads along entire length makingsmoothmuscle as powerful as skeletal muscle – No troponin complex - does contain tropomyosinnottroponin Hasprotein calmodulinthatbindsCa't – Thick and thin filaments arranged diagonally- Contracts in Corkscrewmannerspiral wholelayercontractsnotjustonecell – Intermediate filament–dense body network- Contain lattice-like arrangement of noncontractile intermediate filaments that resist tension _______________: Dense bodies proteins that anchor filaments to sarcolemma at regular intervals – Correspond to Z discs of skeletal muscle During contraction, areas of sarcolemma between dense bodies bulge outward – Make muscle cells look puffy Contraction of Smooth Muscle Mechanism of contraction – Slow, synchronized contractions – Cells electrically coupled by __________________________ gap junctions Action potentials transmitted from fiber to fiber – Some cells are self-excitatory (depolarize without external stimuli) no stimuli Act as __________________ pacemakers for sheets of muscle Rate and intensity of contraction may be modified by neural and chemical stimuli – Contraction in smooth muscle is similar to skeletal muscle contraction in following ways: Actin myosin interact by slidingfilament mechanism Need Ca't to trigger ATPenergizes slidingprocess Contraction stopswhen Ca't is no longeravailable – Contraction in smooth muscle is different from skeletal muscle in following ways: Extracellular Some Cast fromSRbutmostfrom space at binds to calmodulin not troponin fibril or sarcomere No myo Corkscrewsmoothmuscle to contractmyosinactininteract differently Clinical – Homeostatic Imbalance Muscular ________________________: dystrophy group of inherited muscle-destroying diseases – Generally appear in childhood What happens to muscles with this disease? musclesenlarge as a result of fat and CT deposits butthenatrophyand degenerate ___________________________ Duchenne muscular dystrophy DMD is the most common and severe type – Caused by: defective genefor dystrophin – How is this inherited? sexlinkedtraitcarriedbyfemales and expressed in males 13600  – Dystrophin is a cytoplasmic protein that links the cytoskeleton to the extracellular matrix, stabilizing the sarcolemma Fragile sarcolemma tears during contractions, causing entry of excess Ca2+ o Leads to damaged contractile fibers Inflammatory cells accumulate replaced with When tears is Muscle mass declines Victims become clumsy and fall frequently tissueso muscles degenerate appears between ages 2 and 7 Patients usually die of respiratory failure in their early 20s no known cure