© 2015 Pearson Education, Inc.

10-1 An Introduction to Muscle Tissue
Learning Outcomes 10-1 Specify the functions of skeletal muscle tissue. 10-2 Describe the organization of muscle at the tissue level. 10-3 Describe the characteristics of skeletal muscle fibers, and identify the structural components of a sarcomere. 10-4 Identify the components of the neuromuscular junction, and summarize the events involved in the neural control of skeletal muscle contraction and relaxation. © 2015 Pearson Education, Inc.

Learning Outcomes 10-5 Describe the mechanism responsible for tension production in a muscle fiber, and compare the different types of muscle contraction. 10-6 Describe the mechanisms by which muscle fibers obtain the energy to power contractions. 10-7 Relate the types of muscle fibers to muscle performance, and distinguish between aerobic and anaerobic endurance. © 2015 Pearson Education, Inc. 3

Learning Outcomes 10-8 Identify the structural and functional differences between skeletal muscle fibers and cardiac muscle cells. 10-9 Identify the structural and functional differences between skeletal muscle fibers and smooth muscle cells, and discuss the roles of smooth muscle tissue in systems throughout the body. © 2015 Pearson Education, Inc. 4

An Introduction to Muscle Tissue
A primary tissue type, divided into: Skeletal muscle tissue Cardiac muscle tissue Smooth muscle tissue © 2015 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 © 2015 Pearson Education, Inc.

10-1 Functions of Skeletal Muscle Tissue
Six Functions of Skeletal Muscle Tissue Produce skeletal movement Maintain posture and body position Support soft tissues Guard entrances and exits Maintain body temperature Store nutrient reserves © 2015 Pearson Education, Inc.

10-2 Organization of Muscle
Skeletal Muscle Muscle tissue (muscle cells or fibers) Connective tissues Nerves Blood vessels © 2015 Pearson Education, Inc.

Figure 10-1 The Organization of Skeletal Muscles (Part 1 of 3).
Skeletal Muscle (organ) Epimysium Perimysium Endomysium Nerve Muscle fascicle Muscle fibers Blood vessels Epimysium Blood vessels and nerves Tendon Endomysium Perimysium

Figure 10-1 The Organization of Skeletal Muscles (Part 3 of 3).
Muscle Fiber (cell) Capillary Myofibril Endomysium Sarcoplasm Epimysium Blood vessels and nerves Mitochondrion Myosatellite cell Sarcolemma Nucleus Tendon Axon of neuron Endomysium Perimysium

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) © 2015 Pearson Education, Inc.

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) © 2015 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 © 2015 Pearson Education, Inc.

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

Figure 10-2a The Formation of a Multinucleate Skeletal Muscle Fiber.
Muscle fibers develop through the fusion of embryonic cells called myoblasts. Myoblasts a 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

Figure 10-2b The Formation of a Multinucleate Skeletal Muscle Fiber.
Sarcolemma Striations Nuclei Myofibrils Mitochondria b A diagrammatic view and a micrograph of one muscle fiber.

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

Sarcoplasmic reticulum
Figure 10-3 The Structure and Internal Organization of a Skeletal Muscle Fiber. Myofibril Muscle fiber Sarcolemma Nuclei Sarcoplasm Mitochondria Terminal cisterna Sarcolemma Sarcolemma Sarcoplasm Myofibril Myofibrils Thin filament Thick filament Triad Sarcoplasmic reticulum T tubules

Myofibril Muscle fiber Sarcolemma Nuclei Sarcoplasm
Figure 10-3 The Structure and Internal Organization of a Skeletal Muscle Fiber (Part 1 of 4). Myofibril Muscle fiber Sarcolemma Nuclei Sarcoplasm

Sarcoplasmic reticulum
Figure 10-3 The Structure and Internal Organization of a Skeletal Muscle Fiber (Part 2 of 4). Mitochondria Terminal cisterna Sarcolemma Sarcolemma Sarcoplasm Myofibril Myofibrils Thin filament Thick filament Triad Sarcoplasmic reticulum T tubules

Mitochondria Sarcolemma Myofibril Thin filament Thick filament
Figure 10-3 The Structure and Internal Organization of a Skeletal Muscle Fiber (Part 3 of 4). Mitochondria Sarcolemma Myofibril Thin filament Thick filament

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) © 2015 Pearson Education, Inc.

Sarcomeres The A Band M line The center of the A band At midline of sarcomere The H Band The area around the M line Has thick filaments but no thin filaments Zone of overlap The densest, darkest area on a light micrograph Where thick and thin filaments overlap © 2015 Pearson Education, Inc.

Sarcomeres The I Band Z lines The centers of the I bands At two ends of sarcomere Titin Are strands of protein Reach from tips of thick filaments to the Z line Stabilize the filaments © 2015 Pearson Education, Inc.

Figure 10-4a Sarcomere Structure, Longitudinal Views.
I band A band H band Z line Titin a A longitudinal view of a sarcomere, showing bands of thick and thin filaments Zone of overlap M line Thin filament Thick filament Sarcomere

Figure 10-4b Sarcomere Structure, Longitudinal Views.
I band A band H band Z line b A corresponding longitudinal section of a sarcomere in a myofibril from a muscle fiber in the gastrocnemius (calf) muscle of the leg Myofibril TEM × 64,000 Z line Zone of overlap M line Sarcomere

Myofibril Surrounded by: Sarcoplasmic reticulum Consists of:
Figure 10-6 Levels of Functional Organization in a Skeletal Muscle (Part 4 of 5). Myofibril Surrounded by: Sarcoplasmic reticulum Consists of: Sarcomeres (Z line to Z line)

Sarcomere I band A band Contains: Thick filaments Thin filaments
Figure 10-6 Levels of Functional Organization in a Skeletal Muscle (Part 5 of 5). Sarcomere I band A band Contains: Thick filaments Thin filaments Z line M line Titin Z line H band

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

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 © 2015 Pearson Education, Inc.

Figure 10-8a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber. Myofibril at rest I band A band Z line H band Z line a A relaxed sarcomere showing location of the A band, Z lines, and I band.

Figure 10-8b Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber. Contracted myofibril I band A band Z line H band Z line b 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.

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

10-4 Components of the Neuromuscular Junction
Excitation–Contraction Coupling Action potential reaches a triad Releasing Ca2+ Triggering contraction Requires myosin heads to be in “cocked” position Loaded by ATP energy © 2015 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 © 2015 Pearson Education, Inc.

10-4 Skeletal Muscle Relaxation
Ca2+ concentrations fall Ca2+ 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 © 2015 Pearson Education, Inc.

10-4 Skeletal Muscle Contraction and Relaxation
Summary Skeletal muscle fibers shorten as thin filaments slide between thick filaments Free Ca2+ in the sarcoplasm triggers contraction SR releases Ca2+ when a motor neuron stimulates the muscle fiber Contraction is an active process Relaxation and return to resting length are passive © 2015 Pearson Education, Inc.

10-5 Tension Production and Contraction Types
Tension Production by Muscle Fibers Twitches Latent period The action potential moves through sarcolemma Causing Ca2+ release Contraction phase Calcium ions bind Tension builds to peak Relaxation phase Ca2+ levels fall Active sites are covered and tension falls to resting levels © 2015 Pearson Education, Inc.

Tension Production by Muscle 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 © 2015 Pearson Education, Inc.

Motor Units and Tension Production Sustained tension Less than maximum tension Allows motor units to 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 © 2015 Pearson Education, Inc.

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) © 2015 Pearson Education, Inc.

Load and Speed of Contraction Are inversely related The heavier the load (resistance) on a muscle: The longer it takes for shortening to begin And the less the muscle will shorten © 2015 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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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 by- product © 2015 Pearson Education, Inc.

Figure 10-20 Muscle Metabolism (Part 1 of 3).
Muscle Metabolism in a Resting Muscle Fiber • In a resting skeletal muscle, the demand for ATP is low, and there is more than enough oxygen available for mitochondria to meet that demand. Fatty acids O2 G Blood vessels • Resting muscle fibers absorb fatty acids, which are broken down in the mitochondria creating a surplus of ATP. Glucose Glycogen • Some mitochondrial ATP is used to convert absorbed glucose to glycogen. ADP ADP CP • Mitochondrial ATP is also used to convert creatine to creatine phosphate (CP). Mitochondria ATP • This results in the buildup of energy reserves (glycogen and CP) in the muscle. CO2 Creatine

Muscle Metabolism during Moderate Activity • During moderate levels of activity, the demand for ATP increases. Fatty acids O2 • There is still enough oxygen for the mitochondria to meet that demand, but no excess ATP is produced. Glucose Glycogen • The muscle fiber now relies primarily on the aerobic metabolism of glucose from stored glycogen to generate ATP. 2 ADP 2 ATP • If the glycogen reserves are low, the muscle fiber can also break down other substrates, such as fatty acids. Pyruvate 34 ADP • All of the ATP now produced is used to power muscle contraction. 34 ATP CO2 To myofibrils to support muscle contraction

Muscle Metabolism during Peak Activity • During peak levels of activity, the demand for ATP is enormous. Oxygen cannot diffuse into the fiber fast enough for the mitochondria to meet that demand. Only a third of the cell’s ATP needs can be met by the mitochondria (not shown). Lactate Glucose Glycogen • The rest of the ATP comes from glycolysis, and when this produces pyruvate faster than the mitochondria can utilize it, the pyruvate builds up in the cytosol. This process is called anaerobic metabolism because no oxygen is used. 2 ADP ADP CP 2 ATP Pyruvate ATP Creatine • Under these conditions, pyruvate is converted to lactic acid, which dissociates into a lactate ion and a hydrogen ion. Lactate To myofibrils to support muscle contraction H+ • The buildup of hydrogen ions increases fiber acidity, which inhibits muscle contraction, leading to rapid fatigue.

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 pH (lactic acid) Muscle exhaustion and pain © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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) © 2015 Pearson Education, Inc.

10-7 Types of Muscle 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 © 2015 Pearson Education, Inc.

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

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

10-8 Cardiac Muscle Tissue
Cardiac muscle cells are striated and found only in the heart Striations are similar to that of skeletal muscle because the internal arrangement of myofilaments is similar © 2015 Pearson Education, Inc.

Structural Characteristics of Cardiac Muscle Tissue Unlike skeletal muscle, cardiac muscle cells (cardiocytes): Are small Have a single nucleus Have short, wide T tubules Have no triads Have SR with no terminal cisternae Are aerobic (high in myoglobin, mitochondria) Have intercalated discs © 2015 Pearson Education, Inc.

Intercalated Discs Are specialized contact points between cardiocytes Join cell membranes of adjacent cardiocytes (gap junctions, desmosomes) Functions of intercalated discs Maintain structure Enhance molecular and electrical connections Conduct action potentials © 2015 Pearson Education, Inc.

Intercalated Discs Coordination of cardiocytes Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells © 2015 Pearson Education, Inc.

Figure 10-22a Cardiac Muscle Tissue.
Cardiac muscle cell Intercalated discs Nucleus Cardiac muscle tissue LM × 575 a A light micrograph of cardiac muscle tissue.

Figure 10-22b Cardiac Muscle Tissue.
Cardiac muscle cell (intact) Intercalated disc (sectioned) b A diagrammatic view of cardiac muscle. Note the striations and intercalated discs. Mitochondria Nucleus Intercalated discs Cardiac muscle cell (sectioned) Myofibrils

Figure 10-22c Cardiac Muscle Tissue.
Entrance to T tubule Sarcolemma Mitochondrion Contact of sarcoplasmic reticulum with T tubule Sarcoplasmic reticulum Myofibrils c Cardiac muscle tissue showing short, broad T tubules and SR that lacks terminal cisternae.

Functional Characteristics of Cardiac Muscle Tissue Automaticity Contraction without neural stimulation Controlled by pacemaker cells Variable contraction tension Controlled by nervous system Extended contraction time Ten times as long as skeletal muscle Prevention of wave summation and tetanic contractions by cell membranes Long refractory period © 2015 Pearson Education, Inc.

10-9 Smooth Muscle Tissue Smooth Muscle in Body Systems
Forms around other tissues In integumentary system Arrector pili muscles cause “goose bumps” In blood vessels and airways Regulates blood pressure and airflow In reproductive and glandular systems Produces movements In digestive and urinary systems Forms sphincters Produces contractions © 2015 Pearson Education, Inc.

10-9 Smooth Muscle Tissue Structural Characteristics of Smooth Muscle Tissue Nonstriated tissue Different internal organization of actin and myosin Different functional characteristics © 2015 Pearson Education, Inc.

Figure 10-23a Smooth Muscle Tissue.
Circular muscle layer T Longitudinal muscle layer L Smooth muscle tissue LM × 100 a Many visceral organs contain several layers of smooth muscle tissue oriented in different directions. Here, a single sectional view shows smooth muscle cells in both longitudinal (L) and transverse (T) sections.

Figure 10-23b Smooth Muscle Tissue.
Relaxed (sectional view) Dense body Actin Myosin Relaxed (superficial view) Adjacent smooth muscle cells are bound together at dense bodies, transmitting the contractile forces from cell to cell throughout the tissue. Intermediate filaments (desmin) Contracted (superficial view) b A single relaxed smooth muscle cell is spindle shaped and has no striations. Note the changes in cell shape as contraction occurs.

10-9 Smooth Muscle Tissue Characteristics of Smooth Muscle Cells
Long, slender, and spindle shaped Have a single, central nucleus Have no T tubules, myofibrils, or sarcomeres Have no tendons or aponeuroses Have scattered myosin fibers Myosin fibers have more heads per thick filament Have thin filaments attached to dense bodies Dense bodies transmit contractions from cell to cell © 2015 Pearson Education, Inc.

10-9 Smooth Muscle Tissue Functional Characteristics of Smooth Muscle Tissue Excitation–contraction coupling Length–tension relationships Control of contractions Smooth muscle tone © 2015 Pearson Education, Inc.

10-9 Smooth Muscle Tissue Excitation–Contraction Coupling
Free Ca2+ in cytoplasm triggers contraction Ca2+ binds with calmodulin In the sarcoplasm Activates myosin light chain kinase Enzyme breaks down ATP, initiates contraction © 2015 Pearson Education, Inc.

10-9 Smooth Muscle Tissue Length–Tension Relationships
Thick and thin filaments are scattered Resting length not related to tension development Functions over a wide range of lengths (plasticity) © 2015 Pearson Education, Inc.

10-9 Smooth Muscle Tissue Control of Contractions
Multiunit smooth muscle cells Connected to motor neurons Visceral smooth muscle cells Not connected to motor neurons Rhythmic cycles of activity controlled by pacesetter cells © 2015 Pearson Education, Inc.

10-9 Smooth Muscle Tissue Smooth Muscle Tone
Maintains normal levels of activity Modified by neural, hormonal, or chemical factors © 2015 Pearson Education, Inc.

Table 10-3 A Comparison of Skeletal, Cardiac, and Smooth Muscle Tissues.

© 2015 Pearson Education, Inc.

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