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Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Muscle Tissue Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary SEM of partly unraveled skeletal muscle cell exposing the densely packed myofibrils within. Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated Muscle Tissue 1. a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary 2. 3. Muscle is a highly cellular and vascular tissue specialized for contraction via the interaction of myofilaments (between thin and thick filaments); it is responsible for movement of the body and for changes in the size and shape of internal organs. There are three basic types of muscle tissue (skeletal, smooth, and cardiac) classified according to appearance of their contractile cells and location. Striated muscle is formed during development by the fusion of small individual muscle cells called myoblasts into larger, multinucleated myotubes. Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary Learning Objectives 1. Understand the structural features of three general types of muscle cells and how each is organized to form a contractile tissue that performs specific types of work. 2. Understand the structural and functional attributes of connective tissues associated with muscle and the myotendinous junction. 3. Understand that skeletal muscle contains different types of fibers 4. Understand the arrangement of actin and myosin filaments in all three muscle types. 5. Understand the arrangement and roles of transverse tubules, sarcoplasmic reticulum, mitochondria, and contractile filaments in the process of contraction 6. Understand the locations and roles of intercellular junctions in muscle 7. Understand the response of muscle to injury and the regenerative capacity of the various types of muscle. Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. Keywords Learning Objectives 2. Smooth B. Muscle Development (Skeletal) Summary A-band Cardiac muscle Endomysium Epimysium Fascicles I-band Intercalated disc Muscle fiber Myoblast Myocardium Myocytes Myofibrils Myotube Perimysium Sarcoplasmic reticulum Satellite cell Skeletal muscle Smooth muscle Striated muscle Striations T tubule Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary Slide 7: Larynx, Trichrome look here to see skeletal muscle in longitudinal-section look here to see skeletal muscle in cross-section Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. Slide 7: Larynx, Trichrome Introduction 2. Smooth B. Muscle Development (Skeletal) endomysium perimysium Summary individual skeletal muscle fibers (i.e., cells) seen in cross-section epimysium fascicle in skeletal muscle, endomysium is a delicate layer of reticular CT surrounding individual muscle fibers (cells); perimysium is thicker connective tissue surrounding a group of fibers to form a bundle or fascicle; epimysium is a sheath of dense connective tissue surrounding a collection of fascicles that constitute an entire muscle the endo-, peri-, epi- prefixes for surrounding layers of connective tissue will be seen again for other structures, such as the layers of CT surrounding peripheral nerves, so it is important to be familiar with their meaning and usage Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth Slide 70: Tongue, H&E surface of tongue; what specific type of tissue is this? B. Muscle Development (Skeletal) Summary skeletal muscle skeletal muscle (or visceral striated muscle, as seen in the tongue) is generally responsible for voluntary movement within the body, mainly of the skeleton but also other structures such as the eyes and upper esophagus for swallowing; it is composed of long multinucleated cells called muscle fibers which generally extend the entire length of a muscle from tendon to tendon (up to 2ft long in the sartorius muscle in the thigh) Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Slide 70: Tongue, H&E skeletal muscle in longitudinal-section Summary skeletal muscle in cross-section Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle Slide 70: Tongue, H&E 1. Striated notice that the nuclei of the skeletal muscle fibers have been displaced to the periphery of the fiber/cell by all the myofibrils filling the cell a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary endomysium surrounds individual muscle fibers perimysium surrounds the entire muscle fascicle (composed of multiple muscle fibers/cells) Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary Slide 8: Tongue, Trichrome skeletal muscle in longitudinal-section skeletal muscle fiber in cross-section fibroblast of the endomysium CT nucleus of a muscle fiber displaced to the periphery, directly under the sarcolemma skeletal muscle in longitudinal-section numerous capillaries can be seen in the endomysium between the muscle fibers using the know size of an RBC, estimate the diameter of an adjacent muscle fiber Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary Slide 17 (464): Skeletal Muscle, H&E a few nuclei of fibroblasts, forming the endomysium or perimysium, may be seen but can be difficult to identify; the nuclei of endothelial cells of capillaries can also be seen nuclei of skeletal muscle fibers are displaced to the periphery of the cells directly beneath the sarcolemma cross-striations (fine lines) are the alternating dark and light bands formed by the arrangement of the myofilaments of the sarcomere (best seen in electron micrographs); the dark bands are the A-bands (overlapping actin and myosin filaments) and the light bands are the I-bands (actin filaments); the visible striations are the reason both skeletal and cardiac muscle are classified as striated muscle Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle Slide 139: Heart, H&E 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary cardiac muscle is striated muscle, like skeletal muscle; however, it is localized to the walls of the heart and is distinguishable by: (1) the branching of its muscle fibers; (2) a single nucleus per cell, generally round and found near the center of the cell; and (3) the presence of intercalated discs between cells, so that the fibers are actually many cells linked end-to-end, unlike the fibers of skeletal muscle which are a single multinucleated cell Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. Slide 139: Heart, H&E Introduction 2. Smooth B. Muscle Development (Skeletal) Summary what is this “wear and tear” pigment found near the nuclei in cardiac fibers? “branching” of fibers is characteristic of cardiac muscle round, centralized nucleus of cardiac muscle is distinct from the multinucleated peripheral, elongated nuclei of skeletal muscle cross-striations (thin, faint lines) intercalated disc (thick, dark lines) myofibrils (parallel to fiber direction) intercalated discs are highly specialized cell-to-cell adhesion junctions found in cardiac muscle; they physically bind cells together to create long muscle fibers, so the force of contraction is transmitted between the cells; they also promote the spread of action potentials from cell to cell via gap junctions Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Slide 66: Esophagus, H&E lumen Summary look in the outer layer to see smooth muscle in cross-section look in the inner layer to see smooth muscle in longitudinal-section Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. Slide 66: Esophagus, H&E 2. Smooth B. Muscle Development (Skeletal) Summary elongated, centrallylocated nucleus of smooth muscle fiber seen longitudinally smooth muscle fibers are long and tapered at both ends, generally ranging in length from 20-200µm; there are no striations (hence, “smooth”) because the actin and myosin filaments do not show the same degree and kind of organization as seen in striated muscle (skeletal and cardiac); like in cardiac muscle, there is a single, central nucleus for each cell; however, in smooth muscle the nucleus conforms to the cell shape, unlike the typically round nucleus of cardiac fibers; it is under involuntary control and is capable of slow, sustained contractions Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary Slide 66: Esophagus, H&E skeletal muscle fiber (cross-section) smooth muscle fiber (cross-section) the upper 1/3 of the esophagus is under voluntary control so has skeletal muscle (voluntary muscle); the lower 2/3 is under involuntary control so has smooth muscle (visceral muscle); on this slide, from the middle portion of the esophagus, the transition between the two muscle types can be seen Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated Slide 66: Esophagus, H&E cross-section a. Skeletal b. Cardiac V. longitudinal 2. Smooth B. Muscle Development (Skeletal) Summary capillary capillary unlike skeletal muscle, smooth muscle makes its own surrounding CT, so fibroblasts are much more rare; however, scattered throughout the tissue, the nuclei of endothelial cells (simple squamous epithelium) may be seen lining capillaries Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle Slide 21: Ileum, Trichrome Slide 37: Ileum, H&E 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary smooth muscle in longitudinal-section smooth muscle in cross-section smooth muscle in longitudinal-section smooth muscle in cross-section the entire GI tract, including the esophagus seen previously and the ileum – part of the small intestine – seen above, contains a surrounding layer of smooth muscle called the muscularis; the muscularis is principally composed of two layers of smooth muscle, with fibers in one layer having perpendicular orientation to the adjacent layer; contraction of these layers allows the GI “tube” to both shorten in length and reduce the diameter of its lumen Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle Slide 159: Fetal Mouse Head Slide Overview developing brain 1. Striated a. Skeletal b. Cardiac V. 2. Smooth cartilaginous nasal septum B. Muscle Development (Skeletal) Summary look in the oral cavity at the tongue to see developing skeletal muscle vertebrae endochondral ossification newly-forming woven bone of the mandible Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle Slide 159: Fetal Mouse Head 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary myoblasts are the skeletal muscle precursor cells found interspersed amongst the myotubes myotubes during embryonic development, mesenchymal myoblast cells fuse to form multinucleated myotubes, which will later further differentiate to form mature, striated skeletal muscle fibers Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Slide 40a (464): Fetal Tongue, H&E Keywords Slides A. Types of Muscle 1. Striated Slide 12a (464): Guinea Pig Head a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary the development of skeletal muscle in the tongue by the fusion of myoblasts into myotubes can be seen on several other slides Slide 130: Fetal Skull Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Common Confusion: Smooth Muscle vs. Dense Regular CT Smooth muscle: muscle found in the walls of vessels and organs, so also known as visceral muscle; it lacks the striated appearance of skeletal and cardiac muscle Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary Smooth muscle Look for: (1) long, tapered cells with a central nucleus conforming to the cell’s shape; (2) nuclei are intracellular, and there are rarely fibroblasts; (3) nuclei appear somewhat clustered and aligned, as the thickest part of one cell stacks against the thinnest part of adjacent cell; (4) nuclei may appear ‘wavy’ if cells are contracted; (5) more abundant vasculature or other tissue types may be visible Dense regular CT: connective tissue proper with thick bundles of collagen arranged in parallel to provide maximal tensile strength along one axis; it is found in tendons, ligaments, capsules, and aponeuroses Dense regular CT Look for: (1) eosinophilic collagen is regular and densely packed; (2) nuclei are fewer and often highly flattened but can have more varied appearance; (3) nuclei located between collagen bundles (i.e., they don’t appear to be ‘intracellular’); (4) vasculature is usually poor and sparse Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Common Confusion: Smooth Muscle vs. Cardiac Muscle in Cross-Section Smooth muscle: muscle found in the walls of vessels and organs, so is also known as visceral muscle; it lacks the striated appearance of skeletal and cardiac muscle Slides A. Types of Muscle Look for: (1) fusiform shape of cells gives the appearance of cells of differing widths; (2) higher density of nuclei due to packing of cells, but nuclei often appear in clusters rather than uniformly distributed; (3) tight packing makes discernment of individual cells often difficult 1. Striated a. Skeletal b. Cardiac V. 2. Smooth B. Muscle Development (Skeletal) Summary Smooth muscle Cardiac muscle: striated muscle found in the walls of the heart; in cross-section it is quickly distinguished from skeletal muscle by the location of the nuclei Look for: (1) generally abundant endomysium with interspersed fibroblasts and capillaries; (2) myofibrils fill the muscle fibers; (3) lipofuscin granules may be seen Cardiac muscle Lab 9 – Muscle Tissue I. II. III. IV. IUSM – 2016 Introduction Learning Objectives Keywords Slides A. Types of Muscle Summary 1. 1. Striated a. a. Skeletal b. Cardiac V. Striated muscle includes both skeletal muscle and cardiac muscle; it is identified by the presence of a distinct cross-striation pattern of alternating lighter-staining Ibands and darker-staining A-bands. 2. Smooth b. B. Muscle Development (Skeletal) Summary 2. 3. Skeletal muscle fibers (under voluntary control) are long, cylindrical multinucleated cells with peripherally-located nuclei; the fibers are formed by the fusion of numerous mesenchymal myoblast cells during development. Cardiac muscle, found within the heart, differs from skeletal muscle by having only one or two centrally-located round nuclei, branching fibers, and intercalated discs (join cells end-to-end). Smooth muscle is muscle found in the walls of vessels and organs, so is also known as visceral muscle; it is called smooth because it lacks the sarcomere organization and striated appearance of skeletal and cardiac muscle; it is under involuntary control and is capable of slow, sustained contractions. Entire skeletal muscles are surrounded by dense connective tissue called epimysium; from the epimysium, less-dense and thinner perimysium extends inward and divides the muscle into fascicles (bundles of muscle fibers); a thin layer of reticular connective tissue, called endomysium, surrounds individual muscle fibers. Within all the layers of the connective tissue there are blood vessels, nerves, and lymphatics. Lab 9 – Muscle Tissue I. II. III. IV. Introduction Learning Objectives Keywords Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac V. Comparison of Different Muscle Types IUSM – 2016 2. Smooth B. Muscle Development (Skeletal) Summary Skeletal Muscle Locations Function Striated? Multinucleated? Location of nuclei Cell shape Branching? Cell junctions Connective tissue layers Regeneration mechanism Sketch of fibers Cardiac Muscle Smooth Muscle