© 2013 Pearson Education, Inc. PowerPoint ® Lecture Slides prepared by Meg Flemming Austin Community College C H A P T E R The Muscular System 7

© 2013 Pearson Education, Inc. Chapter 7 Learning Outcomes 7-1 – Specify the functions of skeletal muscle tissue. 7-2 – Describe the organization of muscle at the tissue level. 7-3 – Identify the structural components of a sarcomere. 7-4 – Explain the key steps involved in the contraction of a skeletal muscle fiber beginning at the neuromuscular junction. 7-5 – Compare the different types of muscle contractions.

© 2013 Pearson Education, Inc. Chapter 7 Learning Outcomes 7-6 – Describe the mechanisms by which muscles obtain the energy to power contractions. 7-7 – Relate the types of muscle fibers to muscle performance, and distinguish between aerobic and anaerobic endurance. 7-8 – Contrast the structures and functions of skeletal, cardiac, and smooth muscle tissues. 7-9 – Explain how the name of a muscle can help identify its location, appearance, or function.

© 2013 Pearson Education, Inc. Chapter 7 Learning Outcomes 7-10 – Identify the main axial muscles of the body together with their origins, insertions, and actions – Identify the main appendicular muscles of the body together with their origins, insertions, and actions – Describe the effects of aging on muscle tissue – Discuss the functional relationships between the muscular system and other organ systems.

© 2013 Pearson Education, Inc. Five Skeletal Muscle Functions (7-1) 1.Produce movement of the skeleton – By pulling on tendons that then move bones 2.Maintain posture and body position 3.Support soft tissues – With the muscles of the abdominal wall and the pelvic floor 4.Guard entrances and exits – In the form of sphincters 5.Maintain body temperature – When contraction occurs, energy is used and converted to heat

© 2013 Pearson Education, Inc. Checkpoint (7-1) 1.Identify the five primary functions of skeletal muscle.

© 2013 Pearson Education, Inc. Organization of Skeletal Muscle Tissue (7-2) Skeletal muscles – Are organs that contain: Connective tissue Blood vessels Nerves Skeletal muscle tissue Single skeletal muscle cells – Also called skeletal muscle fibers

© 2013 Pearson Education, Inc. Three Layers of Connective Tissue (7-2) 1.Epimysium – Covers the entire muscle 2.Perimysium – Divides the muscle into bundles called fascicles – Blood vessels and nerves are contained in the perimysium 3.Endomysium – Covers each muscle fiber and ties fibers together – Contains capillaries and nerve tissue

© 2013 Pearson Education, Inc. Tendons (7-2) Where the ends of all three layers of connective tissue come together – And attach the muscle to a bone Aponeurosis – A broad sheet of collagen fibers that connects muscles to each other – Similar to tendons, but do not connect to a bone

© 2013 Pearson Education, Inc. Blood Vessels and Nerves (7-2) Extensive network of blood vessels in skeletal muscle – Provides high amounts of nutrients and oxygen To skeletal muscles which have high metabolic needs

© 2013 Pearson Education, Inc. Control of Skeletal Muscle (7-2) Mostly under voluntary control – Must be stimulated by the central nervous system – Axons Push through the epimysium Branch through the perimysium And enter the endomysium – To control individual muscle fibers

© 2013 Pearson Education, Inc. Figure 7-1 The Organization of Skeletal Muscles. Skeletal Muscle (organ) Epimysium PerimysiumEndomysiumNerve Muscle fascicle Muscle fibers Blood vessels Muscle Fascicle (bundle of fibers) Perimysium Muscle fiber Endomysium Epimysium Blood vessels and nerves Endomysium Perimysium Tendon Muscle Fiber (cell) CapillaryMyofibril Endomysium Sarcoplasm Mitochondrion Stem cell Sarcolemma Nucleus Axon of neuron

© 2013 Pearson Education, Inc. Checkpoint (7-2) 2.Describe the connective tissue layers associated with a skeletal muscle. 3.How would severing the tendon attached to a muscle affect the muscle's ability to move a body part?

© 2013 Pearson Education, Inc. Features of Skeletal Muscle Fibers (7- 3) Are specifically organized to produce contraction and have specific names for general cell structures Can be very long and are multinucleated Composed of highly organized structures, giving them a striped or striated appearance

© 2013 Pearson Education, Inc. The Sarcolemma and Transverse Tubules (7-3) The sarcolemma – Specific name of muscle fiber plasma membrane – Has openings across the surface that lead into a network of transverse tubules, or T tubules – T tubules allow for electrical stimuli to reach deep into each fiber The sarcoplasm – Specific name for muscle fiber cytoplasm

© 2013 Pearson Education, Inc. Myofibrils in Muscle Fiber (7-3) Hundreds to thousands in each fiber Are encircled by T tubules and are as long as the entire muscle fiber Are bundles of thick and thin myofilaments – Actin molecules are found in thin filaments – Myosin molecules are found in thick filaments Are the contractile proteins that shorten and are responsible for contraction

© 2013 Pearson Education, Inc. The Sarcoplasmic Reticulum (7-3) Or SR Specialized smooth endoplasmic reticulum Expanded end that is next to the T tubule is the terminal cisternae – Contain high concentrations of calcium ions Triad – A combination of two terminal cisternae and one T tubule

© 2013 Pearson Education, Inc. Sarcomeres (7-3) Smallest functional unit of skeletal muscle fiber Formed by repeating myofilament arrangements Each myofibril has about 10,000 sarcomeres Thick and thin filament arrangements are what produce the striated appearance of the fiber Overlapping filaments define lines and bands

© 2013 Pearson Education, Inc. Sarcomere Lines (7-3) Z lines – Thin filaments at both ends of the sarcomere – Another protein connects the Z lines to the thick filament to maintain alignment M line – Made of connections between the thick filaments

© 2013 Pearson Education, Inc. Sarcomere Bands (7-3) A band – Contains the thick filaments I band – Contains the thin filaments, including the Z line

© 2013 Pearson Education, Inc. Figure 7-2 The Organization of a Skeletal Muscle Fiber. T tubules Terminal cisterna Sarcoplasmic reticulum TriadSarcolemma Mitochondria Thick filament Myofilaments Thin filament MYOFIBRIL The structure of a skeletal muscle fiber. SARCOMERE Z line Zone of overlap M line Myofibril I band H band A band Zone of overlap The organization of a sarcomere, part of a single myofibril. Z line M line Z line A stretched out sarcomere. Z line and thin filaments Active site Z line Actin molecules Thick filaments M line ACTIN STRAND Troponin Tropomyosin Thin filament MYOSIN MOLECULE Myosin tail Myosin head Hinge The structure of a thick filament. The structure of a thin filament.

© 2013 Pearson Education, Inc. Figure 7-2a The Organization of a Skeletal Muscle Fiber. T tubules Terminal cisterna Sarcoplasmic reticulum Triad Sarcolemma Mitochondria Thick filament Myofilaments Thin filament MYOFIBRIL The structure of a skeletal muscle fiber.

© 2013 Pearson Education, Inc. Figure 7-2b The Organization of a Skeletal Muscle Fiber. Z line Zone of overlap M line Myofibril I band H band Zone of overlap A band SARCOMERE The organization of a sarcomere, part of a single myofibril.

© 2013 Pearson Education, Inc. Figure 7-2c The Organization of a Skeletal Muscle Fiber. Z line M line Z line A stretched out sarcomere. Z line and thin filaments Z line Thick filaments M line

© 2013 Pearson Education, Inc. Figure 7-2d The Organization of a Skeletal Muscle Fiber. Active siteActin molecules ACTIN STRAND Troponin Tropomyosin Thin filament The structure of a thin filament.

© 2013 Pearson Education, Inc. Figure 7-2e The Organization of a Skeletal Muscle Fiber. MYOSIN MOLECULE Myosin tail Myosin head Hinge The structure of a thick filament.

© 2013 Pearson Education, Inc. Thin and Thick Filaments (7-3) Actin – A thin twisted protein, with specific active sites for myosin to bind to – At rest, active sites are covered by strands of tropomyosin, held in position by troponin Myosin – A thick filament with tail and globular head that attaches to actin active sites during contraction

© 2013 Pearson Education, Inc. Steps of Contraction (7-3) 1.Calcium released from SR 2.Calcium binds to troponin 3.Change of troponin shape causes tropomyosin to move away from active sites 4.Myosin heads bind to active site, creating cross- bridges, rotate and cause actin to slide over myosin

© 2013 Pearson Education, Inc. Sliding Filament Theory (7-3) Based on observed changes in sarcomere – I bands get smaller – Z lines move closer together – H bands decrease – A bands don't change, indicating that the thin filaments are sliding toward the center

© 2013 Pearson Education, Inc. Figure 7-3 Changes in the Appearance of a Sarcomere during Contraction of a Skeletal Muscle Fiber. I band A band Z line H bandZ line A relaxed sarcomere showing locations of the A band, Z lines, and I band. I band During a contraction, the A band stays the same width, but the Z lines move closer together and the I band gets smaller. Z line H band Z line A band

© 2013 Pearson Education, Inc. Checkpoint (7-3) 4.Describe the basic structure of a sarcomere. 5.Why do skeletal muscle fibers appear striated when viewed through a light microscope? 6.Where would you expect the greatest concentration of calcium ions to be in a resting skeletal muscle fiber?

© 2013 Pearson Education, Inc. The Neuromuscular Junction (7-4) Where a motor neuron communicates with a skeletal muscle fiber – Axon terminal of the neuron An enlarged end that contains vesicles of the neurotransmitter – Acetylcholine (ACh) The neurotransmitter that will cross the synaptic cleft

© 2013 Pearson Education, Inc. The Neuromuscular Junction (7-4) ACh binds to the receptor on the motor end plate Cleft and the motor end plate contain acetylcholinesterase (AChE) – Which breaks down ACh Neurons stimulate sarcolemma by generating an action potential – An electrical impulse

© 2013 Pearson Education, Inc. The cytoplasm of the axon terminal contains vesicles filled with molecules of ace- tylcholine, or ACh. Acetylcho- line is a neurotransmitter, a chemical released by a neuron to change the perme- ability or other properties of another cell’s plasma mem- brane. The synaptic cleft and the motor end plate contain molecules of the enzyme acetylcholinesterase (AChE), which breaks down ACh. VesiclesACh Synaptic cleft Motor end plate AChE Slide 1 Figure 7-4 Skeletal Muscle Innervation.

© 2013 Pearson Education, Inc. The stimulus for ACh release is the arrival of an electrical impulse, or action potential, at the axon terminal. The action potential arrives at the NMJ after traveling along the length of the axon. Arriving action potential Slide 2 Figure 7-4 Skeletal Muscle Innervation.

© 2013 Pearson Education, Inc. When the action potential reaches the neuron’s axon 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 Slide 3 Figure 7-4 Skeletal Muscle Innervation.

© 2013 Pearson Education, Inc. ACh molecules diffuse across the synaptic 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 extracell- ular 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 Slide 4 Figure 7-4 Skeletal Muscle Innervation.

© 2013 Pearson Education, Inc. The sudden inrush of sodium ions results in the generation of an action potential in the sarcolemma. AChE quickly breaks down the ACh on the motor end plate and in the synaptic cleft, thus inactivating the ACh receptor sites. Action potential AChE Slide 5 Figure 7-4 Skeletal Muscle Innervation.

© 2013 Pearson Education, Inc. The Contraction Cycle (7-4) Involves the triads Action potential travels over the sarcolemma, down into the T tubules Causes release of calcium from the SR Calcium binds to troponin and the contraction cycle starts

© 2013 Pearson Education, Inc. Contraction Cycle Begins Myosin head Troponin Actin Tropomyosin Figure 7-5 The Contraction Cycle Slide 1

© 2013 Pearson Education, Inc. Active-Site Exposure Sarcoplasm Active site Figure 7-5 The Contraction Cycle Slide 2

© 2013 Pearson Education, Inc. Cross-Bridge Formation Figure 7-5 The Contraction Cycle Slide 3

© 2013 Pearson Education, Inc. Myosin Head Pivoting Figure 7-5 The Contraction Cycle Slide 4

© 2013 Pearson Education, Inc. Cross-Bridge Detachment Figure 7-5 The Contraction Cycle Slide 5

© 2013 Pearson Education, Inc. Myosin Reactivation Figure 7-5 The Contraction Cycle Slide 6

© 2013 Pearson Education, Inc. Table 7-1 Steps Involved in Skeletal Muscle Contraction and Relaxation

© 2013 Pearson Education, Inc. Checkpoint (7-4) 7.Describe the neuromuscular junction. 8.How would a drug that blocks acetylcholine release affect muscle contraction? 9.What would you expect to happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to calcium ions?

© 2013 Pearson Education, Inc. Contraction Produces Tension (7-5) As sarcomeres contract, so does the entire muscle fiber As fibers contract, tension is created by tendons pulling on bones Movement will occur only if the tension is greater than the resistance Compression is a force that pushes objects – Muscle cells create only tension, not compression

© 2013 Pearson Education, Inc. Contraction Produces Tension (7-5) Individual fibers – Are either contracted or relaxed "On" or "off" – Tension is a product of the number of cross-bridges a fiber contains Variation in tension can occur based on: – The amount of overlap of the myofilaments – The frequency of stimulation The more frequent the stimulus, the more Ca 2+ builds up, resulting in greater contractions

© 2013 Pearson Education, Inc. Contraction Produces Tension (7-5) Whole skeletal muscle organ – Contracts with varying tensions based on: Frequency of muscle fiber stimulation Number of fibers activated

© 2013 Pearson Education, Inc. A Muscle Twitch (7-5) A single stimulus-contraction-relaxation cycle in a muscle fiber or whole muscle Represented by a myogram

© 2013 Pearson Education, Inc. Three Phases of a Muscle Twitch (7-5) 1.Latent period – Starts at the point of stimulus and includes the action potential, release of Ca 2+, and the activation of troponin/tropomyosin 2.Contraction phase – Is the development of tension because of the cross-bridge cycle 3.Relaxation phase – Occurs when tension decreases due to the re-storage of Ca 2+ and covering of actin active sites

© 2013 Pearson Education, Inc. Figure 7-6 The Twitch and Development of Tension. Maximum tension development Tension Stimulus Time (msec) Resting phase Latent period Contraction phase Relaxation phase

© 2013 Pearson Education, Inc. Summation and Tetanus (7-5) Summation – Occurs with repeated, frequent stimuli that trigger a response before full relaxation has occurred Incomplete tetanus – Near peak tension with little relaxation Complete tetanus – Stimuli are so frequent that relaxation does not occur ANIMATION Frog Wave Summation PLAY

© 2013 Pearson Education, Inc. Figure 7-7 Effects of Repeated Stimulations. = Stimulus Maximum tension (in tetanus) Time Summation. Summation of twitches occurs when successive stimuli arrive before the relaxation phase has been completed. Incomplete tetanus. 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. During complete tetanus, the stimulus frequency is so high that the relaxation phase is eliminated; tension plateaus at maximal levels. Tension

© 2013 Pearson Education, Inc. Varying Numbers of Fibers Activated (7-5) Allows for smooth contraction and a lot of control Most motor neurons control a number of fibers through multiple, branching axon terminals

© 2013 Pearson Education, Inc. Motor Unit (7-5) A single motor neuron and all the muscle fibers it innervates – Motor units are dispersed throughout the muscle – Fine control movements Use motor units with very few fibers per neuron – Gross movements Motor units have a high fiber-to-neuron ratio

© 2013 Pearson Education, Inc. Recruitment (7-5) A mechanism for increasing tension to create more movement A graded addition of more and more motor units to produce adequate tension

© 2013 Pearson Education, Inc. Figure 7-8 Motor Units. Axons of motor neurons SPINAL CORD Motor nerve Muscle fibers Motor unit 1 Motor unit 2 Motor unit 3 KEY

© 2013 Pearson Education, Inc. Muscle Tone and Atrophy (7-5) Muscle tone – Some muscles at rest will still have a little tension – Primary function is stabilization of joints and posture Atrophy – Occurs in a muscle that is not regularly stimulated – Muscle becomes small and weak – Can be observed after a cast comes off a fracture

© 2013 Pearson Education, Inc. Types of Contraction (7-5) Isotonic contraction – When the length of the muscle changes, but the tension remains the same until relaxation – For example, lifting a book Isometric contraction – When the whole muscle length stays the same, the tension produced does not exceed the load – For example, pushing against a wall

© 2013 Pearson Education, Inc. Elongation of Muscle after Contraction (7-5) No active mechanism for returning a muscle to a pre-contracted, elongated state Passively uses a combination of: – Gravity – Elastic forces – Opposing muscle movement

© 2013 Pearson Education, Inc. Checkpoint (7-5) 10.What factors are responsible for the amount of tension a skeletal muscle develops? 11.A motor unit from a skeletal muscle contains 1500 muscle fibers. Would this muscle be involved in fine, delicate movements or in powerful, gross movements? Explain. 12.Can a skeletal muscle contract without shortening? Explain.

© 2013 Pearson Education, Inc. ATP and CP Reserves (7-6) At rest, muscle cells generate ATP, some of which will be held in reserve Some is used to transfer high energy to creatine forming creatine phosphate (CP)

© 2013 Pearson Education, Inc. ATP and CP Reserves (7-6) During contraction each cross-bridge breaks down ATP into ADP and a phosphate group – CP is then used to recharge ATP The enzyme creatine phosphokinase (CPK or CK) regulates this reaction – It lasts for about 15 seconds ATP must then be generated in a different way

© 2013 Pearson Education, Inc. Aerobic Metabolism (7-6) Occurs in the mitochondria – Using ADP, oxygen, phosphate ions, and organic substrates from carbohydrates, lipids, or proteins Substrates go through the citric acid cycle – A series of chemical reactions that result in energy to make ATP, water, and carbon dioxide Oxygen supply decides ATP aerobic production

© 2013 Pearson Education, Inc. Glycolysis (7-6) Breaks glucose down to pyruvate in the cytoplasm of the cell If pyruvate can go through the citric acid cycle with oxygen, it is very efficient – Forming about 34 ATP With insufficient oxygen, pyruvate yields only 2 ATP Pyruvate is converted to lactic acid – Potentially causing a pH problem in cells

© 2013 Pearson Education, Inc. Figure 7-9 Muscle Metabolism. Fatty acids G Blood vessels Glucose Glycogen Mitochondria Creatine Resting: Fatty acids are catabolized; the ATP produced is used to build energy reserves of ATP, CP, and glycogen. Fatty acids GlucoseGlycogen Pyruvate To myofibrils to support muscle contraction Moderate activity: Glucose and fatty acids are catabolized; the ATP produced is used to power contraction. Lactate Glucose Glycogen Pyruvate Creatine 2 2 To myofibrils to support muscle contraction Peak activity: Most ATP is produced through glycolysis, with lactate and hydrogen ions as by-products. Mitochondrial activity (not shown) now provides only about one-third of the ATP consumed. Lactate

© 2013 Pearson Education, Inc. Figure 7-9a Muscle Metabolism. Fatty acids Blood vessels Glucose G Glycogen Mitochondria Creatine Resting: Fatty acids are catabolized; the ATP produced is used to build energy reserves of ATP, CP, and glycogen.

© 2013 Pearson Education, Inc. Figure 7-9b Muscle Metabolism. Fatty acids GlucoseGlycogen Pyruvate 2 34 To myofibrils to support muscle contraction 34 2 Moderate activity: Glucose and fatty acids are catabolized; the ATP produced is used to power contraction.

© 2013 Pearson Education, Inc. Peak activity: Most ATP is produced through glycolysis, with lactate and hydrogen ions as by-products. Mitochondrial activity (not shown) now provides only about one-third of the ATP consumed. Lactate Glucose Glycogen Pyruvate Lactate Creatine To myofibrils to support muscle contraction 2 2 Figure 7-9c Muscle Metabolism.

© 2013 Pearson Education, Inc. Muscle Fatigue (7-6) Caused by depletion of energy reserves or a lowering of pH – Muscle will no longer contract even if stimulated Endurance athletes, using aerobic metabolism, can draw on stored glycogen and lipids Sprinters, functioning anaerobically, deplete CP and ATP rapidly, and build up lactic acid ANIMATION Frog Fatigue PLAY

© 2013 Pearson Education, Inc. The Recovery Period (7-6) Requires "repaying" the oxygen debt by continuing to breathe faster – Even after the end of exercise, and recycling lactic acid Heat production occurs during exercise – Raising the body temperature Blood vessels in skin will dilate; sweat covers the skin and evaporates – Promoting heat loss

© 2013 Pearson Education, Inc. Checkpoint (7-6) 13.How do muscle cells continuously synthesize ATP? 14.What is muscle fatigue? 15.Define oxygen debt.

© 2013 Pearson Education, Inc. Muscle Performance (7-7) Measured in force – The maximum amount of tension produced by a muscle or muscle group Measured in endurance – The amount of time a particular activity can be performed Two keys to performance 1.Types of fibers in muscle 2.Physical conditioning or training

© 2013 Pearson Education, Inc. Fast Fibers (7-7) The majority of muscle fibers in the body Large in diameter Large glycogen reserves Few mitochondria Rely on glycolysis Are rapidly fatigued

© 2013 Pearson Education, Inc. Slow Fibers (7-7) About half the diameter of, and three times slower than, fast fibers Are fatigue resistant because of three factors 1.Oxygen supply is greater due to more perfusion 2.Myoglobin stores oxygen in the fibers 3.Oxygen use is efficient due to large numbers of mitochondria

© 2013 Pearson Education, Inc. Percentages of Muscle Types Vary (7-7) Fast fibers appear pale and are called white muscles Extensive vasculature and myoglobin in slow fibers cause them to appear reddish and are called red muscles Human muscles are a mixture of fiber types and appear pink

© 2013 Pearson Education, Inc. Muscle Conditioning and Performance (7-7) Physical conditioning and training – Can increase power and endurance Anaerobic endurance – Is increased by brief, intense workouts – Hypertrophy of muscles results Aerobic endurance – Is increased by sustained, low levels of activity

© 2013 Pearson Education, Inc. Checkpoint (7-7) 16. Why would a sprinter experience muscle fatigue before a marathon runner would? 17. Which activity would be more likely to create an oxygen debt in an individual who regularly exercises: swimming laps or lifting weights? 18. Which type of muscle fibers would you expect to predominate in the large leg muscles of someone who excels at endurance activities such as cycling or long- distance running?

© 2013 Pearson Education, Inc. Cardiac Muscle Tissue (7-8) Found only in heart Cardiac muscle cells – Relatively small with usually only one central nucleus – Striated and branched – Intercalated discs, which connect cells to other cells – Communicate through gap junctions, allowing all the fibers to work together

© 2013 Pearson Education, Inc. Cardiac Pacemaker Cells (7-8) Exhibit automaticity Make up only 1 percent of myocardium Establish rate of contraction

© 2013 Pearson Education, Inc. Cardiac Contractile Cells (7-8) 99 percent of myocardium Contract for longer period than skeletal muscle fibers Unique sarcolemmas make tetanus impossible Are permeable to calcium Rely on aerobic metabolism

© 2013 Pearson Education, Inc. Smooth Muscle Tissue (7-8) Found in the walls of most organs, in the form of sheets, bundles, or sheaths Lacks myofibrils, sarcomeres, or striations Smooth muscle cells – Also smaller than skeletal fibers – Spindle-shaped and have a single nucleus