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Chapter 12 Study Guide

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Biological Sciences

CHAPTER 12 MUSCLES Pages 397 407 - 3 types of muscle tissue occur in human body: skeletal muscle, cardiac muscle, and smooth muscle - Most skeletal muscles are attached to bones of skeleton, enabling these muscles to control body movement - Cardiac muscle is found only in heart and is responsible for moving blood through the circulatory system. Skeletal and cardiac muscle are classified as striated muscles - Smooth muscle primary muscle of internal organs and tubes, such as stomach, urinary bladder, and blood vessels. Primary function influence movement of material into, out of, and within the body - Skeletal muscles often described as voluntary muscles, and smooth and cardiac muscle as involuntary. They contract only in response to a signal from a somatic motor neuron. They cannot initiate their own contraction, nor is their contraction influenced directly by hormones - In contrast, cardiac and smooth muscle have multiple levels of control - Activity of cardiac and smooth muscle is subject to modulation by endocrine system. Despite these differences, smooth and cardiac muscle share many properties with skeletal muscle SKELETAL MUSCLE - make up bulk of muscle in body - constitute about 40 % of total body weight - responsible for positioning and moving skeleton - usually attached to bones by tendons made of collagen - origin of a muscle is the end of the muscle that is attached closest to the trunk or to the more stationary bone - insertion of muscle is more distal or more mobile attachment - if centres of the connected bones are brought closer together when the muscle contracts, the muscle is called a flexor (fig 12-2 on pg.398) - if the bones move away form each other when the muscle contracts, the muscle is called is an extensor , and the movement extension - most joints in body have both flexor and extensor muscles, since a contracting muscle can pull a bone in one direction but cannot push it back. - Flexor-extensor pairs are called antagonistic muscle groups since exert opposite effects - Biceps brachii act as flexor, and the triceps brachii act as the extensor. When biceps muscle contracts, the hand and forearm move toward the shoulder. When the triceps contracts, flexed forearm moves away from the shoulder. When one muscle contracts and shortens, the antagonistic muscle must relax and lengthen Skeletal muscles are composed of muscle fibers - skeletal muscle collection of muscle fibers - each skeletal muscle fiber long, cylindrical cell with up to several hundred nuclei on surface of fiber - these muscle fibers are the largest cells in body, created by fusion of many individual embryonic muscle cells - fibers in a given muscle arranged with their long axes in parallel, and each skeletal muscle fiber is sheathed in connective tissue - groups of adjacent fibers bundled together into units fascicles - entire muscle enclosed in a connective tissue sheath that is continuous with the connective tissue around the muscle fibers and fascicles and with tendons holding muscle to underlying bones Muscle Fiber Anatomy - cell membrane of a muscle fiber sarcolemma www.notesolution.com
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