Chapter 10

I. INTRODUCTION

A. Motionresults from alternating contraction (shortening) and relaxation of muscles;the skeletal system offers leverage and also a supportive frame for thismovement.

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B. Thescientific study of muscles is known as myology.

II. OVERVIEW of MUSCLE TISSUE

A. Typesof Muscle Tissue

1. Skeletalmuscle organization is mainly attached to bones. It is striated and voluntary.

2. Cardiacmuscle tissue develops the wall surface of the heart. The is striated and also involuntary.

3. Smooth(visceral) muscle tissue is situated in viscera. The is nonstriated(smooth) and involuntary.

4. Table4.4 to compare the different types of muscle.

5. Seepp. 130 � 132 because that the histology the the 3 species of muscle.

B. Functionsof Muscle Tissue

1. Throughsustained contraction of alternative contraction and relaxation, muscleperforms four crucial functions.

2. Thesefunctions are manufacturing of human body movements, stabilizing body positions, movingsubstances within the body, and also generating heat.

C. Propertiesof Muscle Tissue

1. Electricalexcitability is the ability to answer to particular stimuli by producingelectrical signals together as activity potential (impulse).

2. Contractilityis the ability to shorten and also thicken (contract), generating force to perform work.

a. Inan isometric contraction, the muscle develops tension but does notshorten.

b. Inan isotonic contraction, the tension remains continuous while the muscleshortens.

3. Extensibilityis the capacity to be prolonged (stretched) without damaging the tissue.

4. Elasticityis the capacity to return to initial shape after contraction or extension.

III. SKELETAL MUSCLE TISSUE

A. Eachskeletal muscle is a separate organ composed that cells dubbed fibers.

B. ConnectiveTissue Components

1. Fascia is asheet or band of fibrous connective organization that is deep to the skin andsurrounds muscles and other organs of the body.

a. Superficial fascia (or subcutaneous layer) off muscle from skin (Figure 11.21)and attributes to carry out a pathway because that nerves and also blood vessels, shop fat,insulates, and protects muscles from trauma.

b. Deep fascia,which present the body wall surface and limbs and holds muscles with similar functionstogether, allows totally free movement the muscles, carries nerves, blood vessels, andlymph vessels, and fills spaces between muscles.

2. Otherconnective tissue components are epimysium,covering the whole muscle; perimysium,covering fasciculi; and also endomysium,covering individual muscle fibers; every are expansions of deep fascia (Figure10.1).

3. Tendons and also aponeuroses are expansions of connective tissue(including the epi, peri,and endomysium) past muscle cells that attachmuscle to bone or various other muscle.

a. A tendon is acord of dense connective tissue that attaches a muscle come the periosteum of a bone (Figure 11.22).

b. Anaponeurosis is a tendon the extends as abroad, flat layer (Figure 11.4c).

C. Nerveand Blood supply (Figure 10.2)

1. Nerves(containing engine neurons) convey impulses for muscular contraction.

2. Bloodprovides nutrients and also oxygen for contraction.

D. MicroscopicAnatomy the a skeleton Muscle Fiber

1. Duringembryonic development, bones muscle yarn arise from myoblasts(Figure 10.3a). A couple of myoblasts persist in matureskeletal muscle together satellite cells.

2. Sarcolemma, T Tubules, and also Sarcoplasm

a. Skeletalmuscle consists of fibers (cells) extended by a sarcolemma(Figure 10.3b).

b. Thefibers save on computer T tubules and also sarcoplasm

1) T tubules aretiny invaginations that the sarcolemma that quicklyspread the muscle activity potential come all parts of the muscle fiber.

2) Sarcoplasm is the muscle cabinet cytoplasm and also contains a largeamount the glycogen for energy production and also myoglobinfor oxygen storage.

3. Myofibrilsand Sarcoplasmic Reticulum

a. Eachfiber has myofibrils that consist the thin and thick filaments (myofilaments) (Figure 10.3b).

b. Thesarcoplasmic illusion encircles eachmyofibril. It is comparable to smooth endoplasmic reticulum in nonmusclecells and in the serene muscle shop calcium ions. A T tubule and twoterminal cisterns the the sarcoplasmic illusion oneither side of it kind a triad.

4. Muscular atrophy is a wasting far of muscles, whereas muscular hypertrophy is anincrease in the diameter the muscle yarn (Clinical Application).

5. Filamentsand the Sarcomere

a. Myofibrils arecomposed the thick and thin filaments (Figure 10.3b) i ordered it in units dubbed sarcomeres (Figure 10.4a).

b. Sarcomeres are the basic functional units of a myofibril andshow distinct dark (A band) and also light (I band) locations (Figure 10.4b).

1) Thedarker middle section is the A tape consisting generally of the thickfilaments through some slim filaments overlapping the special ones (zones ofoverlap) (Figure 10.4b).

2) Thelighter sides space the ns bands thatconsist of thin filaments just (Figure 10.4b).

3) AZ key passes through the center of the i band.

4) Anarrow H zone in the center of each A bandcontains thick but no slim filaments.

5) Figure10.5 shows the relationship of the zones, bands, and lines as watched in atransmission electron micrograph.

6) Exercisecan result in torn sarcolemma, damaged myofibrils,and disrupted Z discs (Clinical Application).

6. MuscleProteins

a. ContractileProteins create force during contraction.

1) Myosin, the maincomponent of special filaments, features as a engine protein (Figure 10.6a).Motor proteins push or pull your cargo to accomplish movement by convertingenergy indigenous ATP right into mechanical power of motion or force. The head of themyosin molecule includes an ATPase enzyme.

2) Actin, the key component of slim filaments, connects to themyosin for the sliding together of the filaments (Figures 10. 4b, 10.6b).

b. Regulatoryproteins aid switch the contractions on and off.

1) Theregulatory proteins tropomyosin and troponin room a part of the slim filament.(Figure10.6b)

2) Inrelaxed muscle, tropomyosin, i m sorry is hosted in placeby troponin, block the myosin-binding website on actin preventing myosin native binding come actin.

c. Structuralproteins save the thick and thin filaments in the suitable alignment, provide themyofibril elasticity and also extensibility, and also link the myofibrils come the sarcolemma and extracellularmatrix. An example is Titin, which helps a sarcomere return to its resting size after a muscle hascontracted or to be stretched.

IV. CONTRACTION and RELAXATION OFSKELETAL MUSCLE FIBERS

A. Duringmuscle contraction, myosin overcome bridges pull on thin filaments, leading to themto on slide inward toward the H ar (Figure 10.7); Z discs come towards each otherand the sarcomere shortens, but the thick and thinfilaments execute not readjust in length. The slide of filaments and also shortening that sarcomeres reasons the shortening the the entirety muscle fiberand ultimately the whole muscle. This is called the sliding filamentmechanism.

B. TheContraction Cycle

1. Atthe beginning of contraction, the sarcoplasmicreticulum releases calcium ions which bind to troponinand reason the troponin-tropomysium complicated to uncoverthe myosin-binding website on actin. As soon as the bindingsites room �free�, the contraction cycle begins.

2. Thecontraction bicycle is a repeating succession of events that reasons thefilaments to slide. It is composed of ATP hydrolysis, attachment of myosin come actin to kind cross bridges, the power stroke, anddetachment of myosin from actin (Figure 10.8).

C. Excitation-ContractionCoupling

1. Anincrease in calcium ion concentration in the cytosolstarts muscle contraction; a decrease, stop it.

2. Themuscle action potential release calcium ion from the sarcoplasmicreticulum that combine with troponin, causing it topull on tropomyosin to adjust its orientation, thusexposing myosin-binding sites on actin (Figure 10.9)and permitting the actin and myosin to bind together.

3. Theuse of calcium ions to remove the contraction inhibitor and the joining of actin and also myosin constitute the excitation-contractioncoupling, the actions that connect excitation (a muscleaction potential propagation v the T tubules) to contraction of themuscle fiber.

4. Calcium ion active transport pumps return calcium ion to the sarcoplasmicreticulum.

5. Rigor mortis,a state the muscular rigidity adhering to death, results from a absence of ATP tosplit myosin-actin cross bridges (ClinicalApplication).

D. Length-TensionRelationship

1. Theforcefulness the muscle contraction relies on the size of the sarcomeres in ~ a muscle prior to contraction begins.

2. Figure10.10 plots the length-tension relationship for bones muscle.

E. TheNeuromuscular Junction

1. Muscleaction potentials arise at the neuromuscular junction (NMJ), the synapsebetween a somatic motor neuron and a skeletal muscle fiber (Figure 10.11a).

2. Asynapse is a an ar of communication in between two neurons or a neuron anda target cell.

a. Synapsesseparate cell from direct physical contact.

b. Neurotransmitters bridge that gap.

3. Theneurotransmitter in ~ a NMJ is acetylcholine (ACh).

4. Anerve action potential elicits a muscle action potential v the relax ofacetylcholine, activation the ACh receptor on themotor finish plate, production of a muscle activity potential, and termination of ACh activity �by acetylcholinesterase.(Figure 10.11c).

F. Figure10.12 summarizes the events that occur throughout contraction and also relaxation of askeletal muscle fiber.

V. MUSCLE METABOLISM

A. Activemuscle cells require big quantities the ATP. There room three sources for ATPproduction in muscle cells.

1. Creatine phosphate and ATP can power maximal muscle contraction for around 15seconds and is provided for maximal brief bursts of energy (e.g., 100-meter dash)(Figure 10.13a).

a. Creatine phosphate is unique to muscle fibers.

2. Thepartial catabolism that glucose to generate ATP occurs in anaerobic cellularrespiration (Figure 10.13b). This system can carry out enough energy forabout 30-40 seconds of maximal muscle task (e.g., 300-meter race).

3. Muscularactivity lasting much more than 30 seconds depends progressively on aerobiccellular respiration (reactions inquiry oxygen). This system of ATPproduction involves the finish oxidation the glucose via moving respiration(biological oxidation) (Figure 10.13c).

a. Muscletissue has actually two sources of oxygen: diffusion indigenous blood and release by myoglobin within muscle fibers.

b. Theaerobic device will provide enough ATP for an extensive activity so lengthy assufficient oxygen and nutrients space available.

B. Theinability of a muscle to maintain its strength of convulsion or tension iscalled muscle fatigue; the occurs as soon as a muscle cannot develop enough ATPto satisfy its needs.

C. Elevatedoxygen usage after practice is called recovery oxygen usage (ratherthan the formerly used term oxygen debt).

VI. CONTROL of MUSCLE TENSION

A. Whenconsidering the contraction of a totality muscle, the stress it deserve to generatedepends ~ above the variety of fibers that are contracting in unison.

B. Amotor neuron and the muscle yarn it stimulates type a engine unit(Figure 10.14). A single motor unit might innervate as few as 10 or as plenty of as2,000 muscle fibers, v an typical of 150 fibers gift innervated through eachmotor neuron.

C. Atwitch contraction is a short contraction of every the muscle yarn in amotor unit in solution to a single action potential.

1. Arecord of a muscle convulsion is dubbed a myogramand has three periods: latent, contraction, and relaxation (Figure10.15).

2. Therefractory duration is the time when a muscle has actually temporarily lostexcitability through skeletal muscles having a short refractory period and cardiacmuscle having a long refractory period.

D. Frequencyof Stimulation

1. Tide summationis the increased strength of a contraction result from the applications of asecond stimulus prior to the muscle has completely relaxed after ~ a previous stimulus(Figure 10.16a, b).

2. Asustained muscle contraction the permits partial relaxation in between stimuli iscalled incomplete (unfused) tetanus (Figure10.16c); a sustained contraction that lacks even partial be safe betweenstimuli is called finish (fused) tetanus (Figure 10.16d). Most musclecontractions are asynchronous incomplete tetaniccontractions of the engine units quite than finish tetanus.

3. Whena muscle is permitted to relax fully and is stimulated automatically followingrelaxation, the 2nd contraction will be stronger. This have the right to be repetitive witheach contraction acquiring stronger to a maximum point.� This is dubbed treppe(the staircase effect) and is the basis for �warming-up� exercises.

E. Theprocess of raising the variety of active motor units is dubbed recruitment(multiple engine unit summation).

1. Itprevents fatigue and also helps carry out smooth muscular contraction rather than aseries the jerky movements.

2. Aerobictraining builds endurance and anaerobic training build muscle strength.

F. Asustained partial contraction of parts of a calm skeletal muscle resultsin a firmness known as muscle tone. At any given moment, a few musclefibers within a muscle are contracted while many are relaxed. This little amountof contraction is necessary for preserving posture.

G. Isotonic contractions take place when a constant load is moved through the selection of motionspossible in ~ a joint and include concentric contractions (Figure 10.17a)and eccentric contractions (Figure 10.17b); in an isometric contraction,the muscle does no shorten but tension rises (Figure 10.17c). One isometriccontraction can be defined as a contraction which is resisting a musclestretch.

VII. TYPES OF skeletal MSUCLE FIBERS

A. Allskeletal muscle fibers room not similar in structure or duty (Table 10.2).

1. Colorvaries follow to the contents of myoglobin,an oxygen-storing red pigment. Red muscle fibers have ahigh myoglobin content while the myoglobin contents of white muscle yarn is low.

2. Fiberdiameter varies as carry out the cells� allocations the mitochondria, bloodcapillaries, and sarcoplasmic reticulum.

3. Contractionvelocity and also resistance come fatigue likewise differ between fibers.

B. Onthe communication of structure and function, skeletal muscle fibers space classified as slowoxidative, oxidative-glycolytic, and fast glycolytic fibers. See page 295 because that the completedescription of this fibers.

C. Distributionand Recruitment of Different varieties of Fibers

1. Mostskeletal muscles contain a mixture that all three fiber types, their proportionsvarying v the usual activity of the muscle. Every fibers of any kind of one motor unit,however, room the same.

2. Althoughthe number of different skeleton muscle yarn does no change, thecharacteristics of those existing can be transformed by various varieties of exercise.

VIII. CARDIAC MUSCLE TISSUE

A. Cardiacmuscle organization is found only in the heart wall surface (see thing 20).

1. Itsfibers are arranged similarly to skeleton muscle fibers.

2. Cardiac muscle fibers affix to nearby fibers by intercalated discs i m sorry contain desmosomes and also gap junctions (Figure 4.1e).

B. Cardiacmuscle contractions last longer than the bones muscle twitch due to theprolonged distribution of calcium ions from the sarcoplasmicreticulum and the extracellular fluid.

C. Cardiacmuscle fibers contract when stimulated by their very own autorhythmicfibers.

D. Thiscontinuous, rhythmic activity is a significant physiological distinction betweencardiac and skeletal muscle tissue.

IX. SMOOTH MUSCLE

A. Smooth muscletissue is nonstriated and involuntary and isclassified into two types: visceral (single unit) smooth muscle (Figure10.18a) and multiunit smooth muscle (Figure 10.18b).

1. Visceral (single unit) smooth muscle is uncovered in the wall surfaces of hollow viscera and smallblood vessels; the fibers room arranged in a network.

2. Multiunit smooth muscle is found in big blood vessels, big airways, arrector chili muscles, and theiris of the eye. The fibers run singly quite than together a unit.

B. MicroscopicAnatomy the the Smooth Muscle

1. Sarcoplasm of smooth muscle fibers contains both thick and also thinfilaments which room not organized right into sarcomeres.

2. Smoothmuscle yarn contain intermediate filaments which are attached to densebodies. (Figure 10.19)

X. REGENERATION that MUSCLE TISSUE

A. Skeletalmuscle fibers cannot divide and have limited powers the regeneration; growth afterthe very first year is due to enlargement of existing cells, fairly than one increasein the variety of fibers (although brand-new individual cells may be derived from satellitecells).

1. Thenumber of new skeletal muscle fibers formed from satellite cells is minimal.

2. Extensiverepair results in fibrosis, the instead of of muscle fibers by scartissue.

B. Cardiacmuscle yarn cannot divide or regenerate.

C. Smoothmuscle yarn have minimal capacity for department and regeneration.

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D. Table10.2 summarizes the principal features of the three varieties of muscle.