Anatomy & Physiology: The Unity of Form and Function, 7th Edition

Published by McGraw-Hill Education
ISBN 10: 0073403717
ISBN 13: 978-0-07340-371-7

Chapter 11 - Section 11.1 - Types and Characteristics of Muscular Tissue - Before You Go On - Page 399: 2

Answer

There are three types of muscles in the body, skeletal, cardiac and smooth muscle. . Skeletal muscle is distintive to varying degrees because of the followu=ing characteristics: . Skeletal muscle like other muscle types is made up of muscle cells ( myofibers or myocytes). In skeletal muscle the muscle cells are much wider and very much wider than they are in cardiac and smooth muscles. Skeletal muscle is also called striated muscle because the alternating light and dark bands that display when this kind of muscle is examined under a polarized microscope . The dark A are anisotropic and appear dark under polarized light, while the I bands are isotropic and appear light under polarized light. Skeletal muscle and cardiac muscle are striated but smooth muscle is not. Skeletal muscle does not possess the quality of autorhythmicity, but cardiac muscle and single unit smooth muscle cells do. . A skeletal muscle comprises a number of bundles or fascicles of myofibers. Within the muscle cells are long protein cords called myofibrils which include three types of protein filaments called myofilaments--myosin, actin, and elastic filaments. In addition to protein organelles, muscles have associated layers of connective tissues , namely, endomysium, perimysium and epimysium:. the endomysium surrounds individual muscle fibers; perimysium binds muscle fibers into fascicles, and epimysium encloses the entire muscle. Cardiac and smooth muscles have only the endomysial layer; skeletal muscle is distinct in having all three layers. Skeletal muscle cells are multinucleate: they have many nuclei just beneath the cell plasma membrane or sarcolemma. The other types of muscle cells are usually uninucleate. Skeletal muscle cells have abundant smooth endoplasmic reticulum ( sarcoplasmic reticulum) , This organelle is present in other types of muscle cells, but in less abundance. Gap junction which facilitate synchronous excitation and contraction are present in cardiac and smooth muscle but absent from myofibers of skeletal muscles.

Work Step by Step

Skeletal muscles are innervated by voluntary somatic motor fibers, and needs continuou somatic stimulation or they will atrophy. Smooth muscle and cardiac muscles do not need continuous nervous stimulation from external sources. They receive innervation from the autonomic nervous system Some properties that skeletal and cardiac muscles have in common , which are not possessed by smooth muscles include the following; Striate muscles in general have some limited powers of regeneration; they also have Z-discs for filament attachment; calcium ion source is sarcoplasmic reticulum, and calcium receptor is troponin of thin filaments.
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