9 Skeletal Muscle Tissue Lecture Presentation by Lori Garrett © 2018 Pearson Education, Inc. Section 1: Functional Anatomy of Skeletal Muscle Tissue Learning Outcomes 9.1 Describe the functions of skeletal muscle tissue. 9.2 Describe the organization of skeletal muscle at the tissue level. 9.3 Describe the structures of a sarcomere. 9.4 Describe the structures of a thin filament and a thick filament. 9.5 Describe a major characteristic of excitable membranes and its importance in generating an action potential. © 2018 Pearson Education, Inc. Section 1: Functional Anatomy of Skeletal Muscle Tissue Learning Outcomes (continued) 9.6 Identify the components of the neuromuscular junction, and summarize the events involved in the control of skeletal muscles by motor neurons. 9.7 Describe the role of ATP in a muscle contraction, and explain the steps involved in the contraction of a skeletal muscle fiber. © 2018 Pearson Education, Inc. Module 9.1: Skeletal muscle tissue enables body movement and other vital functions Muscle tissue—mostly muscle cells specialized for contraction. 3 types: skeletal muscle, cardiac muscle, smooth muscle Skeletal muscle cell = muscle fiber Skeletal muscle . = an organ made of mostly skeletal muscle tissue, plus connective tissue, nerves, blood vessels . Directly/indirectly attached to bones (hence skeletal muscle) © 2018 Pearson Education, Inc. Module 9.1: Skeletal muscle tissue functions Functions of skeletal muscle tissue 1. Produce body movement Muscle tendons pull and move bones 2. Maintain posture and body Stabilize joints position 3. Support soft tissues Surround, support, and shield internal structures, such as tissues and organs 4..Guard[Insert body fig_09_01A -L.jpgSphincters here] encircle openings; provide entrances/exits voluntary control of swallowing, defecation, and urination 5. Maintain body temperature Contraction uses energy; energy use generates heat 6. Store nutrients Muscle proteins can break down; release amino acids—can be used to synthesize glucose or provide energy © 2018 Pearson Education, Inc. Module 9.1: Skeletal muscle tissue functions Comparison of muscle tissue types Skeletal muscle tissue . Voluntary control . Produce movement by pulling on bones Cardiac muscle tissue . Involuntary . Only in heart . Pumps blood; circulating it in vessels © 2018 Pearson Education, Inc. Module 9.1: Skeletal muscle tissue functions Comparison of muscle tissue types (continued) Smooth muscle tissue . Involuntary . Walls of hollow organs, small arteries © 2018 Pearson Education, Inc. Module 9.1: Review A. Name the three types of muscle tissue, identify where they are found, and list their functions. B. Which muscle types are voluntary, and which are involuntary? Learning Outcome: Describe the functions of skeletal muscle tissue. © 2018 Pearson Education, Inc. Module 9.2: Skeletal muscle contains muscle tissue, connective tissues, blood vessels, and nerves Structure of a skeletal muscle Skeletal muscle = organ Epimysium = dense sheath of collagen fibers around muscle . Separates muscle from other tissues/organs . Connected to deep fascia (dense connective tissue layer—module 4.15) © 2018 Pearson Education, Inc. Module 9.2: Skeletal muscle structure Muscle fascicle = bundle of muscle fibers Perimysium = fibrous layer dividing muscle into compartments . Separates muscle fascicles . Has collagen and elastic fibers; blood vessels and nerves supplying muscle fibers within the fascicle © 2018 Pearson Education, Inc. Module 9.2: Skeletal muscle structure Skeletal muscle fibers = individual muscle cells . Contain myofibrils = bundles of protein filaments Endomysium = thin layer of areolar connective tissue around each muscle fiber; has collagen and elastic fibers, blood vessels/nerves supplying muscle fibers Myosatellite cells = stem cells that help repair damaged muscle tissue © 2018 Pearson Education, Inc. Module 9.2: Skeletal muscle structure Ends of skeletal muscles: connective tissue layers (epimysium, perimysium, endomysium) merge to form a tendon or aponeurosis . Tendon—attaches muscle to specific point on a bone . Aponeurosis—broad sheet with broad attachment to bone(s) . Contracting muscle pulls on tendon or aponeurosis, which pulls on and moves the bone © 2018 Pearson Education, Inc. Skeletal muscle structure © 2018 Pearson Education, Inc. Module 9.2: Skeletal muscle structure Skeletal muscle development Myoblasts = embryonic cells that fuse to form multinucleate cells that differentiate into skeletal muscle fibers. Some myoblasts remain free in endomysium as myosatellite cells that help repair damaged muscle tissue © 2018 Pearson Education, Inc. Module 9.2: Skeletal muscle structure The multinucleate cells differentiate into skeletal muscle fibers (cells) and start producing proteins for contraction Mature muscle cells are quite large compared to other cells . Diameters up to 100 µm . Length up to 30 cm (12 in.) © 2018 Pearson Education, Inc. Module 9.2: Skeletal muscle structure Multiple nuclei = more copies of genes for protein/enzyme production Special terms for skeletal muscle fibers: . Sarcolemma = plasma membrane . Sarcoplasm = cytoplasm © 2018 Pearson Education, Inc. Skeletal muscle development © 2018 Pearson Education, Inc. Module 9.2: Review A. Define tendon and aponeurosis. B. Describe the connective tissue layers associated with skeletal muscle tissue. C. What special terms are used to describe the plasma membrane and cytoplasm of a skeletal muscle fiber? D. How would severing a tendon attached to a muscle affect movement of that limb? Learning Outcome: Describe the organization of skeletal muscle at the tissue level. © 2018 Pearson Education, Inc. Module 9.3: Skeletal muscle fibers contain T tubules and sarco-plasmic reticula that surround contractile myofibrils made up of sarcomeres Myofibrils Myofibril = small cylindrical structures arranged parallel inside muscle fiber; run length of muscle fiber . Myofibril arrangement gives skeletal muscle appearance of having stripes (striations) . Many mitochondria along myofibrils © 2018 Pearson Education, Inc. Module 9.3: Skeletal muscle fiber contents Myofilaments Myofilaments = bundles of protein filaments inside myofibrils . Thin filaments mostly composed of actin . Thick filaments mostly composed of myosin © 2018 Pearson Education, Inc. Module 9.3: Skeletal muscle fiber contents Sarcomeres and striations Sarcomeres = repeating functional units of skeletal muscle fiber . ~10,000 sarcomeres/myofibril, each ~2 µm resting length . Striations: • Z lines • I band • A band • M line • H band © 2018 Pearson Education, Inc. Module 9.3: Skeletal muscle fiber contents Z lines—Junction of adjacent sarcomeres; proteins (actinins) connect thin filaments of adjacent sarcomeres here I band—Lighter band with only thin filaments A band—Dark/dense region containing thick filaments Zone of overlap—Within A band; overlapping thick/thin filaments M line—Center of A band where adjacent thick filaments connect H band—Lighter region on each side of M line with only thick filaments; visible only in resting sarcomeres © 2018 Pearson Education, Inc. Module 9.3: Skeletal muscle fiber contents Sarcolemma Sarcolemma = plasma membrane of a skeletal muscle fiber . Selective permeability allows uneven distribution of +/– charges Reversal of charge is 1st step leading to muscle contraction . Change in charge initiated by nerve cell (neuron) impulse and spreads across entire sarcolemma © 2018 Pearson Education, Inc. Module 9.3: Skeletal muscle fiber contents Transverse tubules (T tubules) . Continuous with sarcolemma and extend into sarcoplasm . Form passageways through muscle fiber and encircle sarcomere © 2018 Pearson Education, Inc. Module 9.3: Skeletal muscle fiber contents Sarcoplasmic reticulum . Similar to smooth endoplasmic reticulum of other cells . Enlarged sections (terminal cisternae) on either side of T tubule . Triad = pair of terminal cisternae and one T tubule © 2018 Pearson Education, Inc. Module 9.3: Skeletal muscle fiber contents Sarcoplasmic reticulum (continued) . Sarcoplasmic reticulum (SR) stores calcium ions that are actively pumped in from cytosol • Calsequestrin = protein that binds calcium inside SR . Muscle contraction starts when stored calcium ions are released from SR into cytosol (via gated calcium channels) © 2018 Pearson Education, Inc. Module 9.3: Review A. Describe the structures of a sarcomere. B. Define transverse tubules. C. Within a resting skeletal muscle fiber, where is the greatest concentration of Ca2+? Learning Outcome: Describe the structures of a sarcomere. © 2018 Pearson Education, Inc. Module 9.4: The sliding of thin filaments past thick filaments produces muscle contraction Structure of thin filaments . Attached to Z lines with actinin . Composed of 4 main proteins: 1. F-actin 2. Nebulin 3. Tropomyosin 4. Troponin © 2018 Pearson Education, Inc. Module 9.4: Sliding filaments Structure of thin filaments (continued) 1. F-actin (filamentous)—twisted double-strand of G-actin • G-actin molecules each have active site for binding myosin 2. Nebulin—holds two strands of G-actin molecules together © 2018 Pearson Education, Inc. Module 9.4: Sliding filaments Structure of thin filaments (continued) 3. Tropomyosin—double-stranded protein wrapped around F-actin • Blocks myosin binding sites on G-actin molecules • Prevents actin/myosin interaction 4. Troponin—made of 3 subunits • Attached to tropomyosin; = troponin-tropomyosin complex • Also attached to G-actin and has binding sites for Ca2+ © 2018 Pearson Education, Inc. Module