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

Muscle Fascicle Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Levels of Functional Organization in a Skeletal Muscle Fiber Muscle Fiber Myofibril Sacromere

Orientation of the SR, T Tubules, and Individual Sacromeres Fig 9.9

Fig 9.6 Thin and Thick Filaments

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 Changes in the appearance of a sarcomere during contraction of a skeletal muscle fiber

Fig 9.8The Effect of Sarcomere Length on Tension

9.9The 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

9.10The Neuromuscular Synapse Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9.11The 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

Organization of Skeletal Muscle Fibers Most muscle fibers contract and shorten to the same degree 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 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 Organization of the fascicles and the relationship between the fascicles and associated tendon can vary 4 different patterns of fascicle arrangements produce: 4 different patterns of fascicle arrangements produce: Parallel, Convergent, Pennate, and Circular muscles

Fascicles are parallel to the long axis of the muscle (most muscles) 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) 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 Contraction – muscle gets shorter but body increases in diameter

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) 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 directions Fibers on opposite sides of the tendon pull in different directions Fig 9.14

Pennate muscles have 1 or more tendons that run through the body, fascicles form an oblique angle to the tendon 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 Have more fibers than a parallel - generates more tension than a parallel muscle of the same size Fig 9.14 Unipennate – all muscle cells are on the same side of the tendon

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 Sphincter, fibers are concentric around an opening or recess Contraction – opening diameter decreases; guard entrances and exits of internal passageways (digestive and urinary tracts) Contraction – opening diameter decreases; guard entrances and exits of internal passageways (digestive and urinary tracts) Fig 9.14

Muscle Terminology (Table 9.2) Origin – remains stationary Origin – remains stationary Insertion – moves Insertion – moves - commonly the origin is proximal to the insertion If the muscle extends from a broad aponeurosis to a narrow tendon: If the muscle extends from a broad aponeurosis to a narrow tendon: Aponeurosis = originTendon = insertion If there are several tendons at one end and just one at the other: If there are several tendons at one end and just one at the other: Multiple = originsSingle = insertion

Muscle Movement Almost all skeletal muscles either originate or insert on the skeleton Almost all skeletal muscles either originate or insert on the skeleton When a muscle moves a portion of the skeleton, that movement may involve: 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 )

Muscle Actions There are 2 methods of describing actions: The first references the bone region affected: 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: 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 Prime movers (agonists) – muscles chiefly responsible for producing a particular movement Synergists – muscle contracts to assist the prime mover in performing that action 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 Antagonists – muscles whose actions oppose that of the agonist - if the agonist produces flexion, the antagonist will produce extension

Muscle Terminology Specific body regions Specific body regions - brachialis Shape of the muscle Shape of the muscle - trapezius Orientation of muscle fibers Orientation of muscle fibers - rectus, transverse, oblique Specific or unusual features Specific or unusual features - biceps (2 origins) Identification of origin and insertion Identification of origin and insertion - sternocleidomastoid Primary functions Primary functions - flexor carpi radialis Reference to actions Reference to actions - buccinator

Levers and Pulleys The muscle force, speed, or direction of movement 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 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 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 First-class levers –seesaw - fulcrum lies between the applied force and the resistance Second-class levers- characteristics include: Second-class levers- characteristics include: - the force is magnified - the resistance moves more slowly and covers a shorter distance Third-class levers – characteristics include: 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 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 9.16Anatomical 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 Skeletal muscle fibers become smaller in diameter and less elastic Tolerance for exercise decreases Tolerance for exercise decreases The ability to recover from muscular injuries decreases The ability to recover from muscular injuries decreases

Figure 9.17The Life Cycle of Trichinella spiralis