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Home , Endomysium, Muscle cell, Muscle fascicle, Muscle tissue, Perimysium, Skeletal muscle

Lab 9 – Muscle IUSM – 2016

I. Introduction II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac 2. Smooth B. Muscle Development (Skeletal) V. Summary

SEM of partly unraveled exposing the densely packed within. Lab 9 – Muscle Tissue IUSM – 2016

I. Introduction II. Learning Objectives III. Keywords Muscle Tissue IV. Slides A. Types of Muscle 1. Muscle is a highly cellular and 1. Striated specialized for contraction via the interaction of a. Skeletal (between thin and thick filaments); b. Cardiac it is responsible for movement of the body and for 2. Smooth changes in the size and shape of internal organs. B. Muscle Development (Skeletal) V. Summary 2. There are three basic types of muscle tissue (skeletal, smooth, and cardiac) classified according to appearance of their contractile cells and location.

3. Striated muscle is formed during development by the fusion of small individual muscle cells called myoblasts into larger, multinucleated myotubes. Lab 9 – Muscle Tissue IUSM – 2016

I. Introduction Learning Objectives II. Learning Objectives III. Keywords 1. Understand the structural features of three general types of muscle cells IV. Slides and how each is organized to form a contractile tissue that performs A. Types of Muscle specific types of . 1. Striated a. Skeletal 2. Understand the structural and functional attributes of connective tissues b. Cardiac associated with muscle and the myotendinous junction. 2. Smooth B. Muscle Development (Skeletal) 3. Understand that skeletal muscle contains different types of V. Summary 4. Understand the arrangement of and filaments in all three muscle types.

5. Understand the arrangement and roles of transverse , , 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 IUSM – 2016

I. Introduction II. Learning Objectives Keywords III. Keywords IV. Slides A. Types of Muscle A-band Myofibrils 1. Striated Myotube a. Skeletal b. Cardiac Sarcoplasmic reticulum 2. Smooth Fascicles Satellite cell B. Muscle Development (Skeletal) I-band Skeletal muscle V. Summary Muscle Striated muscle Myoblast Striations Myocardium T Myocytes Lab 9 – Muscle Tissue IUSM – 2016

I. Introduction Slide 7: , Trichrome II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated a. Skeletal look here to see b. Cardiac skeletal muscle in 2. Smooth longitudinal-section B. Muscle Development (Skeletal) V. Summary

look here to see skeletal muscle in cross-section Lab 9 – Muscle Tissue IUSM – 2016

I. Introduction Slide 7: Larynx, Trichrome II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle endomysium 1. Striated a. Skeletal b. Cardiac 2. Smooth perimysium B. Muscle Development (Skeletal) V. 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 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 , so it is important to be familiar with their meaning and usage Lab 9 – Muscle Tissue IUSM – 2016

I. Introduction Slide 70: , H&E II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated a. Skeletal surface of tongue; b. Cardiac what specific type of tissue is this? 2. Smooth B. Muscle Development (Skeletal) V. 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 but also other structures such as the and upper for swallowing; it is composed of long multinucleated cells called muscle fibers which generally extend the entire length of a muscle from to tendon (up to 2ft long in the in the ) Lab 9 – Muscle Tissue IUSM – 2016

I. Introduction Slide 70: Tongue, H&E II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated a. Skeletal skeletal muscle b. Cardiac in longitudinal-section 2. Smooth B. Muscle Development (Skeletal) V. Summary

skeletal muscle in cross-section Lab 9 – Muscle Tissue IUSM – 2016

I. Introduction Slide 70: Tongue, H&E II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated notice that the nuclei of the a. Skeletal skeletal muscle fibers b. Cardiac have been displaced to the 2. Smooth periphery of the fiber/cell B. Muscle Development (Skeletal) by all the myofibrils filling V. Summary the cell

endomysium surrounds individual muscle fibers

perimysium surrounds the entire (composed of multiple muscle fibers/cells) Lab 9 – Muscle Tissue IUSM – 2016

I. Introduction Slide 8: Tongue, Trichrome II. Learning Objectives III. Keywords skeletal muscle IV. Slides in longitudinal-section A. Types of Muscle 1. Striated skeletal muscle fiber a. Skeletal in cross-section b. Cardiac 2. Smooth fibroblast of the B. Muscle Development (Skeletal) endomysium CT V. Summary nucleus of a muscle fiber displaced to the periphery, directly under the

skeletal muscle in longitudinal-section

numerous 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 IUSM – 2016

I. Introduction Slide 17 (464): Skeletal Muscle, H&E II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle a few nuclei of fibroblasts, 1. Striated forming the endomysium a. Skeletal or perimysium, may be b. Cardiac seen but can be difficult to 2. Smooth identify; the nuclei of B. Muscle Development (Skeletal) endothelial cells of V. Summary 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 (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 IUSM – 2016

I. Introduction Slide 139: , H&E II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac 2. Smooth B. Muscle Development (Skeletal) V. 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 IUSM – 2016

I. Introduction Slide 139: Heart, H&E II. Learning Objectives III. Keywords IV. Slides round, centralized A. Types of Muscle nucleus of cardiac muscle is distinct from 1. Striated the multinucleated a. Skeletal peripheral, elongated b. Cardiac what is this nuclei of skeletal muscle 2. Smooth “wear and tear” B. Muscle Development (Skeletal) pigment found V. Summary near the nuclei cross-striations in cardiac fibers? (thin, faint lines)

intercalated disc (thick, dark lines)

“branching” of fibers myofibrils is characteristic of (parallel to fiber direction) cardiac muscle

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 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 IUSM – 2016

I. Introduction Slide 66: Esophagus, H&E II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac lumen 2. Smooth B. Muscle Development (Skeletal) V. 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 IUSM – 2016

I. Introduction Slide 66: Esophagus, H&E II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac 2. Smooth elongated, centrally- located nucleus of B. Muscle Development (Skeletal) smooth muscle fiber V. Summary 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 IUSM – 2016

I. Introduction Slide 66: Esophagus, H&E II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle skeletal muscle 1. Striated fiber a. Skeletal (cross-section) b. Cardiac 2. Smooth B. Muscle Development (Skeletal) V. Summary 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 IUSM – 2016

I. Introduction Slide 66: Esophagus, H&E II. Learning Objectives III. Keywords IV. Slides cross-section A. Types of Muscle 1. Striated longitudinal a. Skeletal b. Cardiac 2. Smooth B. Muscle Development (Skeletal) V. Summary

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 ) may be seen lining capillaries Lab 9 – Muscle Tissue IUSM – 2016 I. Introduction Slide 21: Ileum, Trichrome Slide 37: Ileum, H&E II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac 2. Smooth B. Muscle Development (Skeletal) V. Summary

smooth muscle smooth muscle smooth muscle in longitudinal-section smooth muscle in longitudinal-section in cross-section 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 IUSM – 2016

I. Introduction Slide 159: Fetal Mouse Head II. Learning Objectives Slide Overview III. Keywords IV. Slides A. Types of Muscle 1. Striated developing a. Skeletal b. Cardiac 2. Smooth B. Muscle Development (Skeletal) cartilaginous V. Summary nasal septum

look in the oral cavity at the tongue to see developing skeletal muscle

newly-forming woven of the mandible

endochondral vertebrae ossification Lab 9 – Muscle Tissue IUSM – 2016

I. Introduction Slide 159: Fetal Mouse Head II. Learning Objectives III. Keywords IV. Slides A. Types of Muscle 1. Striated a. Skeletal b. Cardiac 2. Smooth B. Muscle Development (Skeletal) V. Summary myoblasts are the skeletal muscle precursor cells found interspersed amongst the myotubes

myotubes

during , mesenchymal myoblast cells fuse to form multinucleated myotubes, which will later further differentiate to form mature, striated skeletal muscle fibers Lab 9 – Muscle Tissue IUSM – 2016 Slide 40a (464): Fetal Tongue, H&E

I. Introduction the development of skeletal muscle in the II. Learning Objectives tongue by the fusion of myoblasts into III. Keywords myotubes can be seen on several other slides IV. Slides A. Types of Muscle 1. Striated Slide 12a (464): Guinea Pig Head a. Skeletal b. Cardiac 2. Smooth B. Muscle Development (Skeletal) V. Summary

Slide 130: Fetal Lab 9 – Muscle Tissue IUSM – 2016 Common Confusion:

I. Introduction Smooth Muscle vs. Dense Regular CT II. Learning Objectives III. Keywords Smooth muscle: muscle found in the walls of vessels and organs, so also known as visceral muscle; it lacks the striated IV. Slides appearance of skeletal and cardiac muscle A. Types of Muscle 1. Striated Look for: (1) long, tapered cells with a central nucleus a. Skeletal conforming to the cell’s shape; (2) nuclei are intracellular, and there are rarely fibroblasts; (3) nuclei appear somewhat b. Cardiac clustered and aligned, as the thickest part of one cell stacks 2. Smooth against the thinnest part of adjacent cell; (4) nuclei may B. Muscle Development (Skeletal) appear ‘wavy’ if cells are contracted; (5) more abundant vasculature or other tissue types may be visible V. Summary Smooth muscle

Dense regular CT: connective tissue proper with thick bundles of arranged in parallel to provide maximal tensile strength along one axis; it is found in , , capsules, and aponeuroses

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

Dense regular CT Lab 9 – Muscle Tissue IUSM – 2016 Common Confusion:

I. Introduction Smooth Muscle vs. Cardiac Muscle in Cross-Section II. Learning Objectives III. Keywords Smooth muscle: muscle found in the walls of vessels and organs, so is also known as visceral muscle; it lacks the IV. Slides striated appearance of skeletal and cardiac muscle A. Types of Muscle 1. Striated Look for: (1) fusiform shape of cells gives the appearance of a. Skeletal cells of differing widths; (2) higher density of nuclei due to packing of cells, but nuclei often appear in clusters rather b. Cardiac than uniformly distributed; (3) tight packing makes 2. Smooth discernment of individual cells often difficult B. Muscle Development (Skeletal) V. 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 IUSM – 2016

I. Introduction Summary II. Learning Objectives 1. Striated muscle includes both skeletal muscle and cardiac muscle; it is identified by III. Keywords the presence of a distinct cross-striation pattern of alternating lighter- I- IV. Slides bands and darker-staining A-bands. A. Types of Muscle 1. Striated a. Skeletal muscle fibers (under voluntary control) are long, cylindrical a. Skeletal multinucleated cells with peripherally-located nuclei; the fibers are formed by b. Cardiac the fusion of numerous mesenchymal myoblast cells during development. 2. Smooth B. Muscle Development (Skeletal) b. Cardiac muscle, found within the heart, differs from skeletal muscle by having V. Summary only one or two centrally-located round nuclei, branching fibers, and intercalated discs (join cells end-to-end).

2. 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.

3. 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 vessels, nerves, and lymphatics. Lab 9 – Muscle Tissue Comparison of Different Muscle Types IUSM – 2016 Skeletal Muscle Cardiac Muscle Smooth Muscle I. Introduction II. Learning Objectives Locations III. Keywords IV. Slides Function A. Types of Muscle 1. Striated Striated? a. Skeletal b. Cardiac Multinucleated? 2. Smooth B. Muscle Development (Skeletal) Location of nuclei V. Summary Cell shape

Branching?

Cell junctions

Connective tissue layers

Regeneration mechanism

Sketch of fibers