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The Muscular System Skeletal Muscle Tissue And Muscle Organization Chapter 9 Part III Alireza Ashraf, M.D. Professor of Physical Medicine & Rehabilitation Shiraz Medical school Levels of Functional Organization in a Skeletal Muscle Fiber Muscle Fascicle Muscle Fiber Myofibril Sacromere Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Orientation of the SR, T Tubules, and Individual Sacromeres Fig 9.9 Fig 9.6 Thin and Thick Filaments Changes in the appearance of a sarcomere during contraction of a skeletal muscle fiber During a contraction, the A band stays the same width, but the Z lines move closer together and the I band and H band are reduced in width Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig 9.8 The Effect of Sarcomere Length on Tension 9.9 The Orientation of the Sarcoplasmic Reticulum, T Tubules, and Individual Sarcomeres A triad occurs where a T tubule encircles a sarcomere between 2 terminal cisternae Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 9.10 The Neuromuscular Synapse Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 9.11 The Events in Muscle Contraction Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 9.12 The Arrangement of Motor Units in a Skeletal Muscle Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Organization of Skeletal Muscle Fibers Most muscle fibers contract and shorten to the same degree - variations in skeletal muscle fiber organization can affect the power, range, and speed of movement Muscle fibers of each fascicle bundle lie parallel to one another Organization of the fascicles and the relationship between the fascicles and associated tendon can vary 4 different patterns of fascicle arrangements produce: Parallel, Convergent, Pennate, and Circular muscles Contraction – muscle gets shorter but body increases in diameter Fig 9.14 Fascicles are parallel to the long axis of the muscle (most muscles) Firm attachment by a tendon extends from the free tip to a movable bone of the skeleton – flat bands with aponeuroses; spindle shaped with cordline tendons; have a central body, belly or gaster (‘stomach) Fig 9.14 Muscle fibers cover a broad area, but all fibers come together at a common attachment site and pull on a tendon, a tendinous sheet, or a raphe (band of collagen fibers) Fibers on opposite sides of the tendon pull in different Unipennate – all muscle cells are on the same side of the tendon Fig 9.14 Pennate muscles have 1 or more tendons that run through the body, fascicles form an oblique angle to the tendon Have more fibers than a parallel - generates more tension than a parallel muscle of the same size Fig 9.14 Bipennate Muscle – muscle fibers on both sides of the tendon Fig 9.14 Multipennate – triangular deltoid muscle covers the superior surface of the shoulder joint Fig 9.14 Sphincter, fibers are concentric around an opening or recess Contraction – opening diameter decreases; guard entrances and exits of internal passageways (digestive and urinary tracts) Muscle Terminology (Table 9.2) Origin – remains stationary Insertion – moves - commonly the origin is proximal to the insertion If the muscle extends from a broad aponeurosis to a narrow tendon: Aponeurosis = origin Tendon = insertion If there are several tendons at one end and just one at the other: Multiple = origins Single = insertion Muscle Movement Almost all skeletal muscles either originate or insert on the skeleton When a muscle moves a portion of the skeleton, that movement may involve: abduction, adduction, flexion, extension, circumduction, rotation, pronation, supination, everison, inversion, dorsiflexion, plantar flexion, lateral flexion, opposition, protraction, retraction, elevation, and depression (review pages 210-212) Muscle Actions There are 2 methods of describing actions: The first references the bone region affected: - example, the biceps brachii muscle is said to perform ‘flexion of the forearm’ The second method specifies the joint involved: - example, the action of the biceps brachii muscle is described as ‘flexion of the elbow’ Primary Actions Muscles can be grouped according to their primary actions into 3 types: Prime movers (agonists) – muscles chiefly responsible for producing a particular movement Synergists – muscle contracts to assist the prime mover in performing that action - if a synergist stabilizes the origin of the agonist, it is called a fixator Antagonists – muscles whose actions oppose that of the agonist - if the agonist produces flexion, the antagonist will produce extension Muscle Terminology Specific body regions - brachialis Shape of the muscle - trapezius Orientation of muscle fibers - rectus, transverse, oblique Specific or unusual features - biceps (2 origins) Identification of origin and insertion - sternocleidomastoid Primary functions - flexor carpi radialis Reference to actions - buccinator Levers and Pulleys The muscle force, speed, or direction of movement - produced by its contraction can be modified by attaching the muscle to a lever - the applied force is the effort produced by the contraction - the effort is opposed by a resistance (load or weight) A lever is a rigid structure – board, crowbar, or bone - that moves on a fixed point or fulcrum In the body each bone is a lever and each joint a fulcrum; levers can change 1) direction of an applied force 2) distance and speed of movement produced by a force and 3) the strength of a force Levers and Pulleys: A Systems Design for Movement First-class levers –seesaw - fulcrum lies between the applied force and the resistance Second-class levers - characteristics include: - the force is magnified - the resistance moves more slowly and covers a shorter distance Third-class levers – characteristics include: - speed and distance traveled are increased - the force produced must be great Levers and Pulleys Although every muscle does not operate as part of a lever system, the presence of levers provides speed and versatility far in excess of what we would predict on the basis of muscle physiology alone Levers and Pulleys: A Systems Design for Movement Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Levers and Pulleys: A Systems Design for Movement Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Levers and Pulleys: A Systems Design for Movement Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Levers and Pulleys: A Systems Design for Movement Figure 9.16 Anatomical Pulleys Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Aging and the Muscular System Skeletal muscle fibers become smaller in diameter and less elastic Tolerance for exercise decreases The ability to recover from muscular injuries decreases Figure 9.17 The Life Cycle of Trichinella spiralis