University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2020
Views:

389

Pages:

21
Author:

Athena Harrison

MUSCULAR SYSTEM MUSCLE TISSUE • Provide muscle movement • Move substances through the body • Produce heat to maintain temperature TYPE OF MUSCLES TISSUE: Skeletal muscle Cardiac muscles Smooth muscles. SKELETAL MUSCLE Skeletal (or striated) muscle: • long, cylindrical multinucleated cells (10-100 μm diameter). • Mesenchymal myoblasts--fuse--Myotube--differentiate-- Striated muscle fibers ORGANIZATION OF SKELETAL MUSCLE Muscle tissue are organized by connective tissue: • Epimysium External sheath of dense irregular connective tissue • Perimysium Thin connective tissue layer that immediately surrounds each bundle of muscle fibers • Endomysium Very thin and delicate layer of reticular fibers/scattered fibroblasts ORGANIZATION WITHIN MUSCLE FIBERS • Longitudinally, skeletal muscle fibers show striations of alternating light and dark bands • Contains cylindrical filament bundles called myofibrils that run parallel to the long axis of the fiber • Dark bands are called A bands ; the light bands are called I bands. • The I band is bisected by a dark transverse line (Z disc). • Sarcomere is the repetitive functional subunit of the contractile apparatus (extends between 2 Z discs). SKELETAL MUSCLE FIBER • Sarcomere the structure between two Z discs (Each myofibril consists of a long series of sarcomeres) • Sarcoplasm--- cytoplasm • Sarcolemma---plasma membrane A: A Band I: I Band N: Nucleus of muscle fibe F: Nucleus of fibroblast Z: Z disc H: H zone M: Mitochondria. T-TUBULES AND TERMINAL CISTERNAE (TRIAD) ENERGY AND OXYGEN SOURCES • Glycogen • Myoglobulins TYPES OF MUSCLE FIBERS Slow oxidative (SO) or type I fibers. Fast glycolytic (FG) or type IIb fibers. Fast oxidative-glycolytic (FOG) or type IIa fibers • Type I (slow) Slow contractions over long periods without fatigue, having many mitochondria, many surrounding capillaries, and much myoglobin • Type IIb (fast, FG) Physiological and histological features intermediate between those of the other two types. • Type IIa (fast, FOG) Rapid, short-term contraction, few mitochondria/capillaries and depending on Oxidative phosphorylation (mainly) and anaerobic metabolism, fibers appear white. Rapid contractions -- rapid fatigue due to lactic acid production. CARDIAC MUSCLE - EMBRYOLOGY CARDIAC MUSCLE • 85-100 um in length • 1-2 nuclei • Rich in capillaries • Intercalated discs Interfaces between adjacent cells and consist of many junctional complexes (desmosomes, fascia adherens, and gap junctions. • Mitochondria occupy up to 40% • Fatty acids are the major fuel. • Muscle of the heart ventricles is much thicker • T-tubules in • ventricular muscle fibers are well-developed • Cardiac muscle fiber contraction is intrinsic and spontaneous • Contraction initiated by nodes of unique myocardial fibers • Contraction of individual myocardial fibers is all-ornone • rate of contraction is modified by autonomic innervation • The fibers consist of separate cells joined at interdigitating regions called the intercalated discs. • Intercalated disc have abundant desmosomes and gap junctions. • Have central nuclei and myofibrils which are usually sparser and SMOOTH MUSCLE • Slow and steady contraction • Under the control of autonomic nerves and various hormones. • Present in blood vessels, digestive, respiratory, urinary, and reproductive tracts. • Fibers of smooth muscle are elongated, tapering, and unstriated cells. • Enclosed by an endomysium (a network of type I and type III). • Length is 20 μm - 500 μm. SMOOTH MUSCLES Urinary bladder GI tract CONTRACTION • Dense bodies (similar to Z discs) is located in the cytoplasm and at the cell membrane • Both thin filaments and intermediate • Mitochondria, glycogen granules, and Golgi complexes located centrally near nucleus. • rudimentary sarcoplasmic reticulum • Rich in gap junction • Caveolae are small plasmalemma invaginations which contain signaling components. REGENERATION OF MUSCLE TISSUE THE • In skeletal muscle, although the multinucleated cells cannot undergo mitosis • Mesenchymal satellite cells lying inside the external lamina can participate in limited regeneration. • Cardiac muscle lacks satellite cells • very little regenerative capacity beyond early childhood. • Defects or damage replaced by proliferating fibroblasts and CT formation leading to myocardial scars. • Smooth muscle is capable of a more active regenerative response. • Can undergo mitosis and replace the damaged tissue.

Muscular System

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