ch.04. muscle-tissue2.pptx

Muscle Tissue Kristine Krafts, M.D. Muscle Tissue Lecture Objectives • Describe the location, type of contraction (e.g., strong vs. weak), and histologic features of the three types of muscle. • Compare and contrast the sarcoplasmic reticulum structure, T-tubule location, and formation of diads/tr...

Muscle Tissue Kristine Krafts, M.D. Muscle Tissue Lecture Objectives • Describe the location, type of contraction (e.g., strong vs. weak), and histologic features of the three types of muscle. • Compare and contrast the sarcoplasmic reticulum structure, T-tubule location, and formation of diads/triads in skeletal vs. cardiac muscle. • Draw a sarcomere at rest, showing actin and myosin filaments, Z and M lines, and I, A , and H bands. Describe how the sarcomere changes as contraction Muscle Tissue Lecture Objectives • Describe the unique structural features of smooth muscle which distinguish it from skeletal and cardiac muscle. • Describe the connective tissue sheaths that surround skeletal muscle. • Compare the ability of the three types of muscle to regenerate. Muscle Tissue Lecture Outline • Introduction • Skeletal muscle • Cardiac muscle • Smooth muscle Muscle Tissue Lecture Outline • Introduction Fun facts about muscle terminology • “Sarco-” is from the Greek sarx (flesh) • “Myo-” is from the Greek mys (muscle) • Muscle cells are longer than they are wide, so they are also called “fibers” • There are three types of muscle cells: smooth, skeletal, and cardiac. Smooth muscle cells are non-striated; skeletal and cardiac muscle cells are striated. Don’t make this mistake! “Striated muscle” and “skeletal muscle” are sometimes used interchangeably. This is wrong, wrong, wrong! Skeletal muscle is striated – but so is cardiac muscle. So if you mean skeletal, say skeletal, not striated. Muscle types and activity Summary that will make sense later Skeletal Cardiac Smooth Location Near bones Heart wall Walls of hollow organs and blood vessels Nuclei Many. Flat. Peripheral. 1-2 per cell. Plump. Central. One per cell. Central. Cell diameter Largest Intermediate Smallest Striations Yes Yes No Sarcoplas mic reticulum Yes Yes No T tubules At junction of A-I bands. Form triads. At Z lines. Form diads. None More summary that will make sense later Skeletal Cardiac Smooth Motor control Voluntary Involuntary Involuntary Contraction Quick and Quick, strong, strong rhythmic Slow, in waves Blood supply Moderate Less abundant Other features Intercalated Prominen disks, t fascicles branching cells Extensive Cells overlap; can synthesize collagen and elastin Muscle Tissue Lecture Outline • Introduction • Skeletal muscle Transverse section Longitudinal section Skeletal muscle Where do skeletal muscle cells come from? • Derived from mesenchymal cells, which give rise to myoblasts. • Myoblasts: spindle-shaped. Fuse to form multinucleated myotubes which elongate. • Mature skeletal muscle cells (or fibers): long, unbranched tubes with many flattened nuclei. • Sarcoplasm contains a ton of mitochondria, glycogen granules and myoglobin. Abundant eosinophili c cytoplasm Peripheral nuclei Skeletal muscle Cells are long, unbranche d tubes Can just barely see striations Peripheral, flattened nuclei Skeletal muscle What’s in an actual skeletal muscle? A bunch of fascicles. Each fascicle is composed of a bunch of muscle cells (fibers). Each muscle cell contains a bunch of myofibrils. Connective tissue surrounds the cells, fascicles, and entire muscle. Epimysium Perimysium Connective tissue that surrounds each fascicle Dense layer of connective tissue that surrounds entire muscle Endomysium Delicate connective tissue (reticular fibers and basal lamina) that surrounds each muscle cell (fiber) So what’s in a myofibril? Myofilaments. Thin (actin) filaments Thick (myosin) filaments Bands and sarcomeres • Each myofibril has repeating subunits called sarcomeres which have bands. • The sarcomeres in each myofibril are aligned with those of adjacent myofibrils so their bands are also aligned. • A sarcomere is defined as running from Z line to Z line. Myofibril, bands and sarcomere A band I band Z line Skeletal muscle with A bands, I bands, Z lines Sarcomere and bands When muscles contract, sarcomeres shorten! Thin (actin) filaments Thick (myosin) filaments Actin filaments get pulled toward each other. The distance between the Z lines shortens, Check out this video to see how the sarcomere shortens! https://youtu.be/U2TSaz8-yNQ Summary: bands and lines • A bands are composed of thick (myosin) filaments overlapping thin (actin) filaments. • H bands are in the center of A bands. They lie between the free ends of the thin filaments and contain only myosin filaments. • M lines bisect H bands. They are where adjacent thick filaments connect. • I bands contain only thin filaments. • Z lines (disks) bisect I bands. Alpha Sarcoplasmic reticulum • Sarcoplasmic reticulum is the smooth endoplasmic reticulum in muscle cells. • It is specialized to sequester & release calcium ions. • It surrounds each myofibril. Transverse (T) tubules At each A-I band junction, a tubular invagination of the sarcolemma termed a transverse (T) tubule penetrates the muscle fiber and lies next to the surface of myofibrils. Terminal cisterna and triad • An expansion of the sarcoplasmic reticulum called a terminal cisterna lies on each side of the T tubule. • A triad is a complex of 2 terminal cisternae with a T tubule in between. Muscle Tissue Lecture Outline • Introduction • Skeletal muscle • Cardiac muscle Cardiac muscle Structure of cardiac muscle cells • Cardiac muscle cells are branched and striated. • Intercalated disks glue adjacent cells together. • Sarcoplasmic reticulum is kind of sparse. • T-tubules occur at Z lines and form diads with adjacent sarcoplasmic reticulum. Cardiac Muscle Cells Cardiac Muscle Cells Intercalated Disks Intercalated disks are complexes of several types of cell-cell junctions! • Fascia adherens anchor actin filaments. • Macula adherens (spot desmosomes) prevent cardiac muscle fibers from tearing apart during contraction. • Gap junctions allow electrical stimuli to be passed from cell to cell. Intercalated Disk Fascia adheren s Macula adherens Gap junction Cardiac muscle with plump nuclei (N), intercalated discs (I), and striations (S) Muscle Tissue Lecture Outline • Introduction • Skeletal muscle • Cardiac muscle • Smooth muscle Transverse section Longitudinal section Smooth muscle Location and function of smooth muscle • Most smooth muscle is present in walls of hollow organs (such as intestine and uterus). • Smooth muscle is also present in walls of larger blood vessels and in the eye. • In addition to their contractile properties, smooth muscle cells produce collagen, elastin and proteoglycans. Smooth Muscle Morphology • Smooth muscle cells (fibers) are fusiform (spindleshaped) with single central nucleus. • The width of the fiber or cell is only slightly greater than the width of the nucleus. • They are packed together tightly. More smooth muscle morphology • Abundant mitochondria, some rough ER and large Golgi complex. • Each cell is surrounded by basal lamina and reticular fibers. • Thin (actin) and thick (myosin) filaments are not tightly arranged but just crisscross through cell. • Intermediate filaments (desmin and vimentin) also present in cytoplasm. Smooth muscle: thin and thick filaments Wait, what are dense bodies? • Anchor sites for actin-myosin filament bundles. • Comparable to Z-disks of skeletal and cardiac muscle. • Located along inside of sarcolemma and scattered throughout cytoplasm. Contraction of smooth muscle Relaxed smooth muscle cell Contracted smooth muscle cell Regeneration of muscle tissue Cardiac muscle has no regenerative ability. Death of cardiac muscle leads to replacement by dense connective tissue scar. Skeletal muscle can undergo limited regeneration. Satellite cells are inactive myoblasts that become activated and proliferate and fuse after injury. Smooth muscle is capable of active regeneration. Muscle fibers undergo mitosis and replace damaged tissue. Muscle Tissue Lecture Outline • Introduction • Skeletal muscle • Cardiac muscle • Smooth muscle