An Introduction to Muscle Tissue A primary tissue

An Introduction to Muscle Tissue • A primary tissue type, divided into: • Skeletal muscle tissue • Cardiac muscle tissue • Smooth muscle tissue © 2012 Pearson Education, Inc.

10 -1 Functions of Skeletal Muscle Tissue • Skeletal Muscles • Are attached to the skeletal system • Allow us to move • The muscular system • Includes only skeletal muscles © 2012 Pearson Education, Inc.

10 -1 Functions of Skeletal Muscle Tissue • Six Functions of Skeletal Muscle Tissue 1. Produce skeletal movement 2. Maintain posture and body position 3. Support soft tissues 4. Guard entrances and exits 5. Maintain body temperature 6. Store nutrient reserves © 2012 Pearson Education, Inc.

10 -2 Organization of Muscle • Organization of Connective Tissues • Muscles have three layers of connective tissues 1. Epimysium 2. Perimysium 3. Endomysium © 2012 Pearson Education, Inc.

10 -2 Organization of Muscle • Epimysium • Exterior collagen layer • Connected to deep fascia • Separates muscle from surrounding tissues © 2012 Pearson Education, Inc.

10 -2 Organization of Muscle • Perimysium • Surrounds muscle fiber bundles (fascicles) • Contains blood vessel and nerve supply to fascicles © 2012 Pearson Education, Inc.

10 -2 Organization of Muscle • Endomysium • Surrounds individual muscle cells (muscle fibers) • Contains capillaries and nerve fibers contacting muscle cells • Contains myosatellite cells (stem cells) that repair damage © 2012 Pearson Education, Inc.

Figure 10 -1 The Organization of Skeletal Muscles Skeletal Muscle (organ) Epimysium Perimysium Endomysium Nerve Muscle fascicle Muscle Blood fibers vessels Epimysium Blood vessels and nerves Tendon Endomysium Perimysium © 2012 Pearson Education, Inc.

Figure 10 -1 The Organization of Skeletal Muscles Muscle Fascicle (bundle of fibers) Perimysium Muscle fiber Epimysium Blood vessels and nerves Endomysium Tendon Endomysium Perimysium © 2012 Pearson Education, Inc.

Figure 10 -1 The Organization of Skeletal Muscles Muscle Fiber (cell) Capillary Myofibril Endomysium Sarcoplasm Epimysium Mitochondrion Blood vessels and nerves Tendon Myosatellite cell Sarcolemma Nucleus Axon of neuron Endomysium Perimysium © 2012 Pearson Education, Inc.

10 -2 Organization of Muscle • Organization of Connective Tissues • Muscle Attachments • Endomysium, perimysium, and epimysium come together: • At ends of muscles • To form connective tissue attachment to bone matrix • I. e. , tendon (bundle) or aponeurosis (sheet) © 2012 Pearson Education, Inc.

10 -2 Organization of Muscle • Blood Vessels and Nerves • Muscles have extensive vascular systems that: • Supply large amounts of oxygen • Supply nutrients • Carry away wastes • Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord) © 2012 Pearson Education, Inc.

10 -3 Characteristics of Skeletal Muscle Fibers • Skeletal Muscle Cells • Are very long • Develop through fusion of mesodermal cells (myoblasts) • Become very large • Contain hundreds of nuclei © 2012 Pearson Education, Inc.

Figure 10 -2 The Formation of a Multinucleate Skeletal Muscle Fiber Muscle fibers develop through the fusion of mesodermal cells called myoblasts. Myoblasts A muscle fiber forms by the fusion of myoblasts. LM 612 Muscle fiber Sarcolemma Nuclei Myofibrils Myosatellite cell Nuclei Immature muscle fiber Mitochondria Myosatellite cell A diagrammatic view and a micrograph of one muscle fiber. Up to 30 cm in length Mature muscle fiber © 2012 Pearson Education, Inc.

Figure 10 -2 a The Formation of a Multinucleate Skeletal Muscle Fiber Muscle fibers develop through the fusion of mesodermal cells called myoblasts. Myoblasts A muscle fiber forms by the fusion of myoblasts. Myosatellite cell Nuclei Immature muscle fiber Myosatellite cell Up to 30 cm in length Mature muscle fiber © 2012 Pearson Education, Inc.

Figure 10 -2 b The Formation of a Multinucleate Skeletal Muscle Fiber LM 612 Muscle fiber Sarcolemma Nuclei Myofibrils Mitochondria © 2012 Pearson Education, Inc. A diagrammatic view and a micrograph of one muscle fiber.

10 -3 Characteristics of Skeletal Muscle Fibers • The Sarcolemma and Transverse Tubules • The sarcolemma • The cell membrane of a muscle fiber (cell) • Surrounds the sarcoplasm (cytoplasm of muscle fiber) • A change in transmembrane potential begins contractions © 2012 Pearson Education, Inc.

10 -3 Characteristics of Skeletal Muscle Fibers • The Sarcolemma and Transverse Tubules • Transverse tubules (T tubules) • Transmit action potential through cell • Allow entire muscle fiber to contract simultaneously • Have same properties as sarcolemma © 2012 Pearson Education, Inc.

10 -3 Characteristics of Skeletal Muscle Fibers • Myofibrils • Lengthwise subdivisions within muscle fiber • Made up of bundles of protein filaments (myofilaments) • Myofilaments are responsible for muscle contraction • Types of myofilaments: • Thin filaments • Made of the protein actin • Thick filaments • Made of the protein myosin © 2012 Pearson Education, Inc.

10 -3 Characteristics of Skeletal Muscle Fibers • The Sarcoplasmic Reticulum (SR) • A membranous structure surrounding each myofibril • Helps transmit action potential to myofibril • Similar in structure to smooth endoplasmic reticulum • Forms chambers (terminal cisternae) attached to T tubules © 2012 Pearson Education, Inc.

10 -3 Characteristics of Skeletal Muscle Fibers • The Sarcoplasmic Reticulum (SR) • Triad • Is formed by one T tubule and two terminal cisternae • Concentrate Ca 2+ (via ion pumps) • Release Ca 2+ into sarcomeres to begin muscle contraction © 2012 Pearson Education, Inc.

Figure 10 -3 The Structure of a Skeletal Muscle Fiber Myofibril Sarcolemma Nuclei Sarcoplasm MUSCLE FIBER Mitochondria Terminal cisterna Sarcolemma Sarcoplasm Myofibrils Thin filament Thick filament Triad Sarcoplasmic T tubules reticulum © 2012 Pearson Education, Inc.

Figure 10 -3 The Structure of a Skeletal Muscle Fiber Terminal cisterna Sarcolemma Sarcoplasm Myofibrils Triad Sarcoplasmic T tubules reticulum © 2012 Pearson Education, Inc.

10 -3 Structural Components of a Sarcomere • Sarcomeres • The contractile units of muscle • Structural units of myofibrils • Form visible patterns within myofibrils • A striped or striated pattern within myofibrils • Alternating dark, thick filaments (A bands) and light, thin filaments (I bands) © 2012 Pearson Education, Inc.

Figure 10 -4 a Sarcomere Structure, Part I I band A band H band Z line Titin A longitudinal section of a sarcomere, showing bands Zone of overlap M line Sarcomere © 2012 Pearson Education, Inc. Thin Thick filament

Figure 10 -4 b Sarcomere Structure, Part I I band A band H band A corresponding view of a sarcomere in a myofibril from a muscle fiber in the Myofibril gastrocnemius Z line muscle of the calf TEM 64, 000 Zone of overlap M line Sarcomere © 2012 Pearson Education, Inc. Z line

Figure 10 -5 Sarcomere Structure, Part II Sarcomere Myofibril A superficial view of a sarcomere Thin filament Actinin filaments Thick filament Titin filament Attachment of titin Z line Cross-sectional views of different portions of a sarcomere © 2012 Pearson Education, Inc. I band M line H band Zone of overlap

Figure 10 -6 Levels of Functional Organization in a Skeletal Muscle Myofibril Surrounded by: Sarcoplasmic reticulum Surrounded by: Epimysium Contains: Muscle fascicles Consists of: Sarcomeres (Z line to Z line) Sarcomere I band A band Muscle Fascicle Perimysium Contains: Thick filaments Surrounded by: Perimysium Contains: Muscle fibers Thin filaments Z line M line H band Muscle Fiber Endomysium Surrounded by: Endomysium Contains: Myofibrils © 2012 Pearson Education, Inc. Titin Z line

Figure 10 -7 ab Thick and Thin Filaments Sarcomere H band Actinin Z line Titin Myofibril The gross structure of a thin filament, showing the attachment at the Z line M line Troponin Active site Nebulin Tropomyosin G-actin molecules F-actin strand The organization of G-actin subunits in an F-actin strand, and the position of the troponin–tropomyosin complex © 2012 Pearson Education, Inc.

10 -3 Structural Components of a Sarcomere • Initiating Contraction • Ca 2+ binds to receptor on troponin molecule • Troponin–tropomyosin complex changes • Exposes active site of F-actin © 2012 Pearson Education, Inc.

10 -3 Structural Components of a Sarcomere • Thick Filaments • Contain about 300 twisted myosin subunits • Contain titin strands that recoil after stretching • The mysosin molecule • Tail • Binds to other myosin molecules • Head • Made of two globular protein subunits • Reaches the nearest thin filament © 2012 Pearson Education, Inc.

Figure 10 -7 cd Thick and Thin Filaments Titin The structure of thick filaments, showing the orientation of the myosin molecules © 2012 Pearson Education, Inc. M line Myosin head Myosin tail Hinge The structure of a myosin molecule

10 -3 Structural Components of a Sarcomere • Myosin Action • During contraction, myosin heads: • Interact with actin filaments, forming crossbridges • Pivot, producing motion © 2012 Pearson Education, Inc.

10 -3 Structural Components of a Sarcomere • Sliding Filaments and Muscle Contraction • Sliding filament theory • Thin filaments of sarcomere slide toward M line, alongside thick filaments • The width of A zone stays the same • Z lines move closer together © 2012 Pearson Education, Inc.

Figure 10 -8 a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber I band Z line A band H band Z line A relaxed sarcomere showing location of the A band, Z lines, and I band. © 2012 Pearson Education, Inc.

Figure 10 -8 b Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber I band A band Z line H band Z line During a contraction, the A band stays the same width, but the Z lines move closer together and the I band gets smaller. When the ends of a myofibril are free to move, the sarcomeres shorten simultaneously and the ends of the myofibril are pulled toward its center. © 2012 Pearson Education, Inc.

10 -3 Structural Components of a Sarcomere • Skeletal Muscle Contraction • The process of contraction • Neural stimulation of sarcolemma • Causes excitation–contraction coupling • Muscle fiber contraction • Interaction of thick and thin filaments • Tension production © 2012 Pearson Education, Inc.

Figure 10 -9 An Overview of Skeletal Muscle Contraction Neural control Excitation–contraction coupling Excitation Calcium release triggers Thick-thin filament interaction Muscle fiber contraction leads to Tension production © 2012 Pearson Education, Inc. ATP

10 -4 Components of the Neuromuscular Junction • The Control of Skeletal Muscle Activity • The neuromuscular junction (NMJ) • Special intercellular connection between the nervous system and skeletal muscle fiber • Controls calcium ion release into the sarcoplasm A&P FLIX Events at the Neuromuscular Junction © 2012 Pearson Education, Inc.

Figure 10 -11 Skeletal Muscle Innervation Motor neuron Path of electrical impulse (action potential) Axon Neuromuscular junction Synaptic terminal SEE BELOW Sarcoplasmic reticulum Motor end plate Myofibril © 2012 Pearson Education, Inc. Motor end plate

Figure 10 -11 Skeletal Muscle Innervation The cytoplasm of the synaptic terminal contains vesicles filled with molecules of acetylcholine, or ACh. Acetylcholine is a neurotransmitter, a chemical released by a neuron to change the permeability or other properties of another cell’s plasma membrane. The synaptic cleft and the motor end plate contain molecules of the enzyme acetylcholinesterase (ACh. E), which breaks down ACh. Vesicles The synaptic cleft, a narrow space, separates the synaptic terminal of the neuron from the opposing motor end plate. © 2012 Pearson Education, Inc. Junctional ACh. E fold of motor end plate ACh

Figure 10 -11 Skeletal Muscle Innervation The stimulus for ACh release is the arrival of an electrical impulse, or action potential, at the synaptic terminal. An action potential is a sudden change in the transmembrane potential that travels along the length of the axon. Arriving action potential © 2012 Pearson Education, Inc.

Figure 10 -11 Skeletal Muscle Innervation When the action potential reaches the neuron’s synaptic terminal, permeability changes in the membrane trigger the exocytosis of ACh into the synaptic cleft. Exocytosis occurs as vesicles fuse with the neuron’s plasma membrane. Motor end plate © 2012 Pearson Education, Inc.

Figure 10 -11 Skeletal Muscle Innervation ACh molecules diffuse across the synatpic cleft and bind to ACh receptors on the surface of the motor end plate. ACh binding alters the membrane’s permeability to sodium ions. Because the extracellular fluid contains a high concentration of sodium ions, and sodium ion concentration inside the cell is very low, sodium ions rush into the sarcoplasm. ACh receptor site © 2012 Pearson Education, Inc.

Figure 10 -11 Skeletal Muscle Innervation The sudden inrush of sodium ions results in the generation of an action potential in the sarcolemma. ACh. E quickly breaks down the ACh on the motor end plate and in the synaptic cleft, thus inactivating the ACh receptor sites. Action potential ACh. E © 2012 Pearson Education, Inc.

10 -4 Components of the Neuromuscular Junction • Excitation–Contraction Coupling • Action potential reaches a triad • Releasing Ca 2+ • Triggering contraction • Requires myosin heads to be in “cocked” position • Loaded by ATP energy A&P FLIX Excitation-Contraction Coupling © 2012 Pearson Education, Inc.

Figure 10 -10 The Exposure of Active Sites SARCOPLASMIC RETICULUM Calcium channels open Myosin tail (thick filament) Tropomyosin strand Troponin G-actin (thin filament) Active site Nebulin In a resting sarcomere, the tropomyosin strands cover the active sites on the thin filaments, preventing cross-bridge formation. © 2012 Pearson Education, Inc. When calcium ions enter the sarcomere, they bind to troponin, which rotates and swings the tropomyosin away from the active sites. Cross-bridge formation then occurs, and the contraction cycle begins.

10 -4 Skeletal Muscle Contraction • The Contraction Cycle 1. Contraction Cycle Begins 2. Active-Site Exposure 3. Cross-Bridge Formation 4. Myosin Head Pivoting 5. Cross-Bridge Detachment 6. Myosin Reactivation A&P FLIX The Cross Bridge Cycle © 2012 Pearson Education, Inc.

Figure 10 -12 The Contraction Cycle Begins The contraction cycle, which involves a series of interrelated steps, begins with the arrival of calcium ions within the zone of overlap. Myosin head Troponin Tropomyosin © 2012 Pearson Education, Inc. Actin

Figure 10 -12 The Contraction Cycle Active-Site Exposure Calcium ions bind to troponin, weakening the bond between actin and the troponin– tropomyosin complex. The troponin molecule then changes position, rolling the tropomyosin molecule away from the active sites on actin and allowing interaction with the energized myosin heads. Sarcoplasm Active site © 2012 Pearson Education, Inc.

Figure 10 -12 The Contraction Cycle Cross-Bridge Formation Once the active sites are exposed, the energized myosin heads bind to them, forming cross-bridges. © 2012 Pearson Education, Inc.

Figure 10 -12 The Contraction Cycle Myosin Head Pivoting After cross-bridge formation, the energy that was stored in the resting state is released as the myosin head pivots toward the M line. This action is called the power stroke; when it occurs, the bound ADP and phosphate group are released. © 2012 Pearson Education, Inc.

Figure 10 -12 The Contraction Cycle Cross-Bridge Detachment When another ATP binds to the myosin head, the link between the myosin head and the active site on the actin molecule is broken. The active site is now exposed and able to form another cross-bridge. © 2012 Pearson Education, Inc.

Figure 10 -12 The Contraction Cycle Myosin Reactivation Myosin reactivation occurs when the free myosin head splits ATP into ADP and P. The energy released is used to recock the myosin head. © 2012 Pearson Education, Inc.

10 -4 Skeletal Muscle Contraction • Fiber Shortening • As sarcomeres shorten, muscle pulls together, producing tension • Muscle shortening can occur at both ends of the muscle, or at only one end of the muscle • This depends on the way the muscle is attached at the ends © 2012 Pearson Education, Inc.

Figure 10 -13 Shortening during a Contraction When both ends are free to move, the ends of a contracting muscle fiber move toward the center of the muscle fiber. When one end of a myofibril is fixed in position, and the other end free to move, the free end is pulled toward the fixed end. © 2012 Pearson Education, Inc.

10 -4 Skeletal Muscle Relaxation • Contraction Duration • Depends on: • Duration of neural stimulus • Number of free calcium ions in sarcoplasm • Availability of ATP © 2012 Pearson Education, Inc.

10 -4 Skeletal Muscle Relaxation • Ca 2+ concentrations fall • Ca 2+ detaches from troponin • Active sites are re-covered by tropomyosin • Rigor Mortis • A fixed muscular contraction after death • Caused when: • Ion pumps cease to function; ran out of ATP • Calcium builds up in the sarcoplasm © 2012 Pearson Education, Inc.

10 -4 Skeletal Muscle Contraction and Relaxation • Summary • Skeletal muscle fibers shorten as thin filaments slide between thick filaments • Free Ca 2+ in the sarcoplasm triggers contraction • SR releases Ca 2+ when a motor neuron stimulates the muscle fiber • Contraction is an active process • Relaxation and return to resting length are passive © 2012 Pearson Education, Inc.

Table 10 -1 Steps Involved in Skeletal Muscle Contraction and Relaxation Steps in Initiating Muscle Contraction Motor Synaptic terminal end plate Steps in Muscle Relaxation T tubule Sarcolemma Action potential reaches T tubule ACh released, binding to receptors Sarcoplasmic reticulum releases Ca 2 Active site exposure, cross-bridge formation Ca 2 Actin Myosin ACh broken down by ACh. E Sarcoplasmic reticulum recaptures Ca 2 Active sites covered, no cross-bridge interaction Contraction ends Contraction begins Relaxation occurs, passive return to resting length © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Tension Production by Muscles Fibers • As a whole, a muscle fiber is either contracted or relaxed • Depends on: • The number of pivoting cross-bridges • The fiber’s resting length at the time of stimulation • The frequency of stimulation © 2012 Pearson Education, Inc.

Tension (percent of maximum) Figure 10 -14 The Effect of Sarcomere Length on Active Tension Normal range Decreased length Increased sarcomere length Optimal resting length: The normal range of sarcomere lengths in the body is 75 to 130 percent of the optimal length. © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Tension Production by Muscles Fibers • The Frequency of Stimulation • A single neural stimulation produces: • A single contraction or twitch • Which lasts about 7– 100 msec. • Sustained muscular contractions • Require many repeated stimuli © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Tension Production by Muscles Fibers • Twitches 1. Latent period • The action potential moves through sarcolemma • Causing Ca 2+ release 2. Contraction phase • Calcium ions bind • Tension builds to peak 3. Relaxation phase • Ca 2+ levels fall • Active sites are covered and tension falls to resting levels © 2012 Pearson Education, Inc.

Figure 10 -15 a The Development of Tension in a Twitch Eye muscle Gastrocnemius Tension Soleus Stimulus Time (msec) A myogram showing differences in tension over time for a twitch in different skeletal muscles. © 2012 Pearson Education, Inc.

Figure 10 -15 b The Development of Tension in a Twitch Tension Maximum tension development Stimulus Resting Latent Contraction phase period phase Relaxation phase The details of tension over time for a single twitch in the gastrocnemius muscle. Notice the presence of a latent period, which corresponds to the time needed for the conduction of an action potential and the subsequent release of calcium ions by the sarcoplasmic reticulum. © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Tension Production by Muscles Fibers • Treppe • A stair-step increase in twitch tension • Repeated stimulations immediately after relaxation phase • Stimulus frequency <50/second • Causes a series of contractions with increasing tension © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Tension Production by Muscles Fibers • Wave summation • Increasing tension or summation of twitches • Repeated stimulations before the end of relaxation phase • Stimulus frequency >50/second • Causes increasing tension or summation of twitches © 2012 Pearson Education, Inc.

Figure 10 -16 ab Effects of Repeated Stimulations Stimulus Tension Maximum tension (in tetanus) Maximum tension (in treppe) Time Treppe is an increase in Wave summation. Wave peak tension with each successive stimulus delivered shortly after the completion of the relaxation phase of the preceding twitch. summation occurs when successive stimuli arrive before the relaxation phase has been completed. © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Tension Production by Muscles Fibers • Incomplete tetanus • Twitches reach maximum tension • If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension • Complete tetanus • If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction © 2012 Pearson Education, Inc.

Figure 10 -16 cd Effects of Repeated Stimulations Tension Maximum tension (in tetanus) Time Incomplete tetanus. Complete tetanus. During Incomplete tetanus occurs if the stimulus frequency increases further. Tension production rises to a peak, and the periods of relaxation are very brief. complete tetanus, the stimulus frequency is so high that the relaxation phase is eliminated; tension plateaus at maximal levels. © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Tension Production by Skeletal Muscles • Depends on: • Internal tension produced by muscle fibers • External tension exerted by muscle fibers on elastic extracellular fibers • Total number of muscle fibers stimulated © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Motor Units and Tension Production • Motor units in a skeletal muscle: • Contain hundreds of muscle fibers • That contract at the same time • Controlled by a single motor neuron © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Motor Units and Tension Production • Recruitment (multiple motor unit summation) • In a whole muscle or group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated • Maximum tension • Achieved when all motor units reach tetanus • Can be sustained only a very short time © 2012 Pearson Education, Inc.

Figure 10 -17 a The Arrangement and Activity of Motor Units in a Skeletal Muscle Axons of motor neurons Motor nerve KEY SPINAL CORD Muscle fibers Motor unit 1 Motor unit 2 Motor unit 3 Muscle fibers of different motor units are intermingled, so the forces applied to the tendon remain roughly balanced regardless of which motor units are stimulated. © 2012 Pearson Education, Inc.

Figure 10 -17 b The Arrangement and Activity of Motor Units in a Skeletal Muscle Tension in tendon Motor unit 1 unit 2 unit 3 Time © 2012 Pearson Education, Inc. The tension applied to the tendon remains relatively constant, even though individual motor units cycle between contraction and relaxation.

10 -5 Tension Production and Contraction Types • Motor Units and Tension Production • Sustained tension • Less than maximum tension • Allows motor units rest in rotation • Muscle tone • The normal tension and firmness of a muscle at rest • Muscle units actively maintain body position, without motion • Increasing muscle tone increases metabolic energy used, even at rest © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Motor Units and Tension Production • Contraction are classified based on pattern of tension production • Isotonic contraction • Isometric contraction © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Isotonic Contraction • Skeletal muscle changes length • Resulting in motion • If muscle tension > load (resistance): • Muscle shortens (concentric contraction) • If muscle tension < load (resistance): • Muscle lengthens (eccentric contraction) © 2012 Pearson Education, Inc.

Figure 10 -18 a Concentric, Eccentric, and Isometric Contractions Tendon Muscle contracts (concentric contraction) 2 kg Muscle tension (kg) Amount of load Muscle relaxes Peak tension production Contraction begins Resting length Muscle length (percent of resting length) © 2012 Pearson Education, Inc. Time

Figure 10 -18 b Concentric, Eccentric, and Isometric Contractions Support removed when contraction begins (eccentric contraction) Muscle tension (kg) Peak tension production Support removed, contraction begins 6 kg Resting length 6 kg Time © 2012 Pearson Education, Inc. Muscle length (percent of resting length)

10 -5 Tension Production and Contraction Types • Isometric Contraction • Skeletal muscle develops tension, but is prevented from changing length • iso- = same, metric = measure © 2012 Pearson Education, Inc.

Figure 10 -18 c Concentric, Eccentric, and Isometric Contractions Amount of load Muscle tension (kg) Muscle contracts (isometric contraction) Muscle relaxes Peak tension production Contraction begins 6 kg Length unchanged Muscle length (percent of resting length) 6 kg Time © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Muscle Relaxation and the Return to Resting Length • Elastic Forces • The pull of elastic elements (tendons and ligaments) • Expands the sarcomeres to resting length • Opposing Muscle Contractions • Reverse the direction of the original motion • Are the work of opposing skeletal muscle pairs © 2012 Pearson Education, Inc.

10 -5 Tension Production and Contraction Types • Muscle Relaxation and the Return to Resting Length • Gravity • Can take the place of opposing muscle contraction to return a muscle to its resting state © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • ATP Provides Energy For Muscle Contraction • Sustained muscle contraction uses a lot of ATP energy • Muscles store enough energy to start contraction • Muscle fibers must manufacture more ATP as needed © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • ATP and CP Reserves • Adenosine triphosphate (ATP) • The active energy molecule • Creatine phosphate (CP) • The storage molecule for excess ATP energy in resting muscle • Energy recharges ADP to ATP • Using the enzyme creatine kinase (CK) • When CP is used up, other mechanisms generate ATP © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • ATP Generation • Cells produce ATP in two ways 1. Aerobic metabolism of fatty acids in the mitochondria 2. Anaerobic glycolysis in the cytoplasm © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • Aerobic Metabolism • Is the primary energy source of resting muscles • Breaks down fatty acids • Produces 34 ATP molecules per glucose molecule • Glycolysis • Is the primary energy source for peak muscular activity • Produces two ATP molecules per molecule of glucose • Breaks down glucose from glycogen stored in skeletal muscles © 2012 Pearson Education, Inc.

Table 10 -2 Sources of Energy in a Typical Muscle Fiber © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • Energy Use and the Level of Muscular Activity • Skeletal muscles at rest metabolize fatty acids and store glycogen • During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, or amino acids • At peak activity, energy is provided by anaerobic reactions that generate lactic acid as a byproduct © 2012 Pearson Education, Inc.

Figure 10 -20 Muscle Metabolism Fatty acids Blood vessels Glucose Glycogen Pyruvate Mitochondria Creatine To myofibrils to support muscle contraction Resting muscle: Fatty acids are catabolized; the ATP produced is used to build energy reserves of ATP, CP, and glycogen. Moderate activity: Glucose and fatty acids are catabolized; the ATP produced is used to power contraction. Lactate Glucose Pyruvate Glycogen Creatine Lactate To myofibrils to support muscle contraction Peak activity: Most ATP is produced through glycolysis, with lactate as a by-product. Mitochondrial activity (not shown) now provides only about one-third of the ATP consumed. © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • Muscle Fatigue • When muscles can no longer perform a required activity, they are fatigued • Results of Muscle Fatigue • Depletion of metabolic reserves • Damage to sarcolemma and sarcoplasmic reticulum • Low p. H (lactic acid) • Muscle exhaustion and pain © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • The Recovery Period • The time required after exertion for muscles to return to normal • Oxygen becomes available • Mitochondrial activity resumes © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • Lactic Acid Removal and Recycling • The Cori Cycle • The removal and recycling of lactic acid by the liver • Liver converts lactate to pyruvate • Glucose is released to recharge muscle glycogen reserves © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • The Oxygen Debt • After exercise or other exertion: • The body needs more oxygen than usual to normalize metabolic activities • Resulting in heavy breathing • Also called excess postexercise oxygen consumption (EPOC) © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • Heat Production and Loss • Active muscles produce heat • Up to 70% of muscle energy can be lost as heat, raising body temperature © 2012 Pearson Education, Inc.

10 -6 Energy to Power Contractions • Hormones and Muscle Metabolism • Growth hormone • Testosterone • Thyroid hormones • Epinephrine © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Muscle Performance • Force • The maximum amount of tension produced • Endurance • The amount of time an activity can be sustained • Force and endurance depend on: • The types of muscle fibers • Physical conditioning © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Three Major Types of Skeletal Muscle Fibers 1. Fast fibers 2. Slow fibers 3. Intermediate fibers © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Fast Fibers • Contract very quickly • Have large diameter, large glycogen reserves, few mitochondria • Have strong contractions, fatigue quickly © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Slow Fibers • Are slow to contract, slow to fatigue • Have small diameter, more mitochondria • Have high oxygen supply • Contain myoglobin (red pigment, binds oxygen) © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Intermediate Fibers • Are mid-sized • Have low myoglobin • Have more capillaries than fast fibers, slower to fatigue © 2012 Pearson Education, Inc.

Figure 10 -21 Fast versus Slow Fibers Slow fibers Smaller diameter, darker color due to myoglobin; fatigue resistant LM 170 Fast fibers Larger diameter, paler color; easily fatigued LM 170 © 2012 Pearson Education, Inc. LM 783

Table 10 -3 Properties of Skeletal Muscle Fiber Types © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Muscle Performance and the Distribution of Muscle Fibers • White muscles • Mostly fast fibers • Pale (e. g. , chicken breast) • Red muscles • Mostly slow fibers • Dark (e. g. , chicken legs) • Most human muscles • Mixed fibers • Pink © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Muscle Hypertrophy • Muscle growth from heavy training • Increases diameter of muscle fibers • Increases number of myofibrils • Increases mitochondria, glycogen reserves • Muscle Atrophy • Lack of muscle activity • Reduces muscle size, tone, and power © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Physical Conditioning • Improves both power and endurance • Anaerobic activities (e. g. , 50 -meter dash, weightlifting) • Use fast fibers • Fatigue quickly with strenuous activity • Improved by: • Frequent, brief, intensive workouts • Causes hypertrophy © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Physical Conditioning • Improves both power and endurance • Aerobic activities (prolonged activity) • Supported by mitochondria • Require oxygen and nutrients • Improves: • Endurance by training fast fibers to be more like intermediate fibers • Cardiovascular performance © 2012 Pearson Education, Inc.

10 -7 Types of Muscles Fibers and Endurance • Importance of Exercise • What you don’t use, you lose • Muscle tone indicates base activity in motor units of skeletal muscles • Muscles become flaccid when inactive for days or weeks • Muscle fibers break down proteins, become smaller and weaker • With prolonged inactivity, fibrous tissue may replace muscle fibers © 2012 Pearson Education, Inc.