4Skeletal MuscleUsually attached to bones by tendons- sometimes attached directly to bone (pectoralis major)Origin: closest to the trunk- usually does not move a joint when contracts.Insertion: more distal- moves joint when contractsFlexor: brings bones together- decreases angle at jointExtensor: bones move away- increases angle at jointAntagonistic muscle groups: flexor-extensor pairs- antagonistic muscles are usually in opposite sides.
5Anatomy Summary: Skeletal Muscle Figure 12-3a (1 of 2)
8Anatomy Summary: Skeletal Muscle Figure 12-3a (2 of 2)
9Ultrastructure of Muscle Myosin are motor proteins. 250 myosins join to form the thick filaments. The thin filament is made up of a string of actin with tropomyosin and tropnin attached. Titin and nebulin anchor and stabilize.Figure 12-3e
10Ultrastructure of Muscle Actin and myosin form crossbridgesMyofibrilA bandZ diskI bandM lineH zoneSarcomereThin filamentsTropomyosinTroponinActin chainG-actin moleculeMyosin tailMyosinheadsMyosin molecule(c)(d)(e)Thick filamentsHingeregion(f)TitinNebulinFigure 12-3c–f
11Summary of Muscle Contraction Muscle tension: force created by muscleLoad: weight that opposes contractionContraction: creation of tension in muscleRelaxation: release of tensionFigure 12-7
12Neuromuscular Junction: Overview Terminal boutons- insulate the site of the neuromuscular juction and secrete supportive growth factorsSynaptic cleft- space between the axon terminal and the sarcolemmaAcetylcholine- neurotransmitter released involves calcium and binds to nicotinic receptorsMotor end plate- folds on the sarcolemma of the muscleOn muscle cell surfaceNicotinic receptors
13Anatomy of the Neuromuscular Junction Figure (1 of 3)
14Anatomy of the Neuromuscular Junction Figure (2 of 3)
15Anatomy of the Neuromuscular Junction Figure (3 of 3)
16Mechanism of Signal Conduction Axon terminal (of presynaptic cell)Action potential signals acetylcholine releaseMotor end plate – series of folds in the plasma membrane of the postsynaptic cellTwo acetylcholine bindOpens cation channelNa+ influx – K+ effluxMembrane depolarizedStimulates fiber contraction as a result in increased intracellular calcium concentration
17Events at the Neuromuscular Junction Figure 11-13a
18T-tubules and the Sarcoplasmic Reticulum Figure 12-4
19Excitation-Contraction Coupling Muscle fiberMotor end plateAChAxon terminal ofsomatic motor neuronSarcoplasmic reticulumActinTroponinTropomyosinMyosinheadZ diskMyosin thick filamentM lineT-tubuleDHPreceptorCa2+Somatic motor neuronreleases ACh at neuro-muscular junction.(a)1Figure 12-11a, step 1
20Excitation-Contraction Coupling Muscle fiberMotor end plateAChAxon terminal ofsomatic motor neuronSarcoplasmic reticulumActinTroponinTropomyosinMyosinheadZ diskMyosin thick filamentM lineT-tubuleDHPreceptorCa2+Somatic motor neuronreleases ACh at neuro-muscular junction.Net entry of Na+ through AChreceptor-channel initiatesa muscle action potential.Na+K+(a)potential1Action2Action potentialFigure 12-11a, steps 1–2
22Changes in Sarcomere Length during Contraction PLAYAnimation: Muscular System: Sliding Filament TheoryFigure 12-8
23Regulatory Role of Tropomyosin and Troponin In the relaxed state the myosin head is at 90o but it is unbound to actin because the binding sites on actin are blocked.Figure 12-10a
24Regulatory Role of Tropomyosin and Troponin** PiADPG-actin movesCytosolic Ca2+Tropomyosin shifts,exposing bindingsite on G-actinTNPower strokeInitiation of contractionCa2+ levels increasein cytosol.Ca2+ binds totroponin.Troponin-Ca2+complex pullstropomyosinaway from G-actinbinding site.Myosin bindsto actin andcompletes powerstroke.Actin filamentmoves.(b)12345Figure 12-10b
25The Molecular Basis of Contraction ATPbindingsiteMyosinsitesTight binding in the rigorstate. The crossbridge isat a 45° angle relative tothe filaments.filament45G-actin moleculeATP binds to its binding siteon the myosin. Myosin thendissociates from actin.1234Figure 12-9, steps 1–2
26The Molecular Basis of Contraction The ATPase activity of myosinhydrolyzes the ATP. ADP andPi remain bound to myosin.The myosin head swings overand binds weakly to a newactin molecule. The cross-bridge is now at 90º relative tothe filaments.PiADP90°1234Figure 12-9, steps 3–4
27The Molecular Basis of Contraction At the end of the power stroke,the myosin head releases ADPand resumes the tightly boundrigor state.ADPRelease of Pi initiates the powerstroke. The myosin head rotateson its hinge, pushing the actinfilament past it.PiActin filamentmoves toward M line.123456Figure 12-9, steps 5–6
28The Molecular Basis of Contraction At the end of the power stroke,the myosin head releases ADPand resumes the tightly boundrigor state.ATPbindingsiteADPTight binding in the rigorstate. The crossbridge isat a 45° angle relative tothe filaments.Myosin filament45°G-actin moleculeATP binds to its binding siteon the myosin. Myosin thendissociates from actin.The ATPase activity of myosinhydrolyzes the ATP. ADP andPi remain bound to myosin.The myosin head swings over andbinds weakly to a new actin molecule.The crossbridge is now at 90º relativeto the filaments.Pi90°Release of Pi initiates the powerstroke. The myosin head rotateson its hinge, pushing the actinfilament past it.Actin filamentmoves toward M line.Contraction-relaxationSlidingfilament123456MyosinbindingsitesFigure 12-9
29Muscle Fatigue: Multiple Causes Extended submaximal exerciseDepletion of glycogen storesShort-duration maximal exertionIncreased levels of inorganic phosphateMay slow Pi release from myosinDecrease calcium releasePotassium is another factor in fatigue
30Length-Tension Relationships in Contracting Muscle The strength of the contraction is related to the length before the muscle contracts. Very short fibers do not produce much tension because there is a lot of overlap not allowing for much sliding and not many new crossbridges. At optimum lenght there is an optimum number of cross-bridges to there is optimum tension. At a longer length there is less overlap and less ability to produce optimal forceFigure 12-16
31Electrical and Mechanical Events in Muscle Contraction A twitch is a single contraction-relaxation cycleFigure 12-12
32Summation of Contractions Stimuli is too far apart and allows the muscle to relax and lose tensionIf action potentials come in at a closer time they recruit more fibers and the additive effect results in increased muscle tensionFigure 12-17a
33Summation of Contractions The more stimulus the more fibers recruited until there is a maximum tension but is there is alot of time between the stimulus the muscle relaxes resulting in an unfused tetanusFigure 12-17c
34Summation of Contractions Complete tetanus results when action potentials arrive close enough to not allow the muscle to relax. Maximum tension can only be sustained for a limited time because fatigueFigure 12-17d
35Motor Units: Fine motor movements have more innervations
36Mechanics of Body Movement Isotonic contractions create force and move load- creates force and moves a load.Concentric action is a shortening action- contraction that flexes the joint while working against a loadEccentric action is a lengthening action- contraction that extends the joint while resisting a loadIsometric contractions create force without moving a load- the muscle produces tension and contracts but does not move the joint.
37Isotonic and Isometric Contractions Figure 12-19
38Muscle ContractionDuration of muscle contraction of the three types of muscle- in smooth muscle contraction and relaxation happen slower and can be sustained for a longer time.Figure 12-24
39Smooth Muscle: Properties Uses less energy- can maintain maximum tension while using only a small percentage of the total maximum cross bridgeMaintain force for long periods- allows organs to be tonically contracted and maintain tension for a long time (sphincter muscles)Low oxygen consumption- allows for to maintain tension for a long time without fatiguing (bladder).
40Smooth MuscleSmooth muscle is not studied as much as skeletal muscle becauseIt has more variety- impossible to come up with a single muscle function model- special types for vascular, gastrointestinal, urinary, respiratory, reproductive, and ocularAnatomy makes functional studies difficult- fibers within cells and muscle layers within organs run indifferent directions.It is controlled by hormones, paracrines, and neurotransmittersIt has variable electrical properties- contraction is not triggered only action potentialMultiple pathways influence contraction and relaxation- acts as an integrating center to interpret mutiple excitatory and inhibitory signals that may arrive at the same time
41Smooth Muscle Locations IV. Smooth Muscle- A tissue formed by uninucleated spindle shaped cells found in six areas of the body: blood vessel walls, respiratory tract, digestive tubes, urinary organs, reproductive organs, and the eye.
44Muscle DisordersMuscle cramp: sustained painful contraction – hyperexcitability of the motor unit, countered with stretchingOveruse – excessive use that causes tearing in the muscle structures (fibers, sheaths, tendon connection)Disuse- loss of muscle activity causes muscle atrophy because of loss of blood flow, can recover is disuse is less than a yearAcquired disorders – infectious diseases and toxin poisoning that lead to muscle weakness or paralysisInherited disorders -Duchenne’s muscular dystrophy – muscle degenrates from pelvis up, happens most often in women, people live to be 20-30, die of respiratory failureDystrophin –links actin to proteins in cell membraneMcArdle’s disease – limited exercise toleranceGlycogen to glucose-6-phosphate – enzyme missing thus muscles do not have the energy source available.