The Muscular System Skeletal Muscle Tissue And Muscle

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 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 n 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 n Muscle fibers of each fascicle bundle lie parallel to one another n Organization of the fascicles and the relationship between the fascicles and associated tendon can vary n 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) n 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) n

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) n Fibers on opposite sides of the tendon pull in different n

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 n Have more fibers than a parallel - generates more tension than a parallel muscle of the same size n

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 n Contraction – opening diameter decreases; guard entrances and exits of internal passageways (digestive and urinary tracts) n

Muscle Terminology (Table 9. 2) n Origin – remains stationary n Insertion – moves - commonly the origin is proximal to the insertion n If the muscle extends from a broad aponeurosis to a narrow tendon: Aponeurosis = origin n Tendon = insertion If there are several tendons at one end and just one at the other: Multiple = origins Single = insertion

Muscle Movement n Almost all skeletal muscles either originate or insert on the skeleton n 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: n The first references the bone region affected: - example, the biceps brachii muscle is said to perform ‘flexion of the forearm’ n 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: n Prime movers (agonists) – muscles chiefly responsible for producing a particular movement n 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 n 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 n Shape of the muscle - trapezius n Orientation of muscle fibers - rectus, transverse, oblique n n n 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 n 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) n A lever is a rigid structure – board, crowbar, or bone - that moves on a fixed point or fulcrum n 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 n First-class levers –seesaw - fulcrum lies between the applied force and the resistance n Second-class levers - characteristics include: - the force is magnified - the resistance moves more slowly and covers a shorter distance n Third-class levers – characteristics include: - speed and distance traveled are increased - the force produced must be great

Levers and Pulleys n 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 n Skeletal muscle fibers become smaller in diameter and less elastic n Tolerance for exercise decreases n The ability to recover from muscular injuries decreases

Figure 9. 17 The Life Cycle of Trichinella spiralis