دکترامیر هوشنگ واحدی متخصص طب فیزیکی و توانبخشی قسمت 1 body muscels system 1 دکترامیر هوشنگ واحدی متخصص طب فیزیکی و توانبخشی قسمت 1

B. Anatomy of Skeletal Muscles - Gross Anatomy Surrounds muscle Bundle of muscle fibers Surrounds each muscle fiber, and tie adjacent fibers together Divides muscle into compartments, each contain a bundle of muscle fibers called fascicle

Structural Organization of Skeletal Muscle Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Structural Organization of Skeletal Muscle

The Formation and Structure of a Skeletal Muscle Fiber

Development of a skeletal muscle fiber Sarcomere Structure Fig 9.4

Levels of Functional Organization in a Skeletal Muscle Fiber Muscle Fascicle Muscle Fiber Myofibril Sacromere

Orientation of the SR, T Tubules, and Individual Sacromeres

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

The Effect of Sarcomere Length on Tension

The Neuromuscular Synapse

The Events in Muscle Contraction

The Arrangement of Motor Units in a Skeletal Muscle

Nerve Stimulus to Muscles Skeletal muscles must be stimulated by a nerve to contract Motor unit One neuron Muscle cells stimulated by that neuron

Neuromuscular junction, microscopic view

Skeletal Muscle Innervation Each muscle fiber is stimulated by a nerve fiber usually located midway along its length - the synaptic terminal of the neuron is bound to the motor end plate (specialized area of the muscle cell membrane) - entensive vascular supply delivers oxygen and nutrients

The Neuromuscular Junction axon axon terminal motor unit 1 neuron and all the muscles it stimulates

The Sliding Filament Theory of Muscle Contraction Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament Myosin heads then bind to the next site of the thin filament Figure 6.7 Slide 6.17a

The Sliding Filament Theory of Muscle Contraction This continued action causes a sliding of the myosin along the actin The result is that the muscle is shortened (contracted)

The Sliding Filament Theory

Contraction of a Skeletal Muscle Muscle fiber contraction is “all or none” Within a skeletal muscle, not all fibers may be stimulated during the same interval Different combinations of muscle fiber contractions may give differing responses Graded responses – different degrees of skeletal muscle shortening

Energy for Muscle Contraction Initially, muscles used stored ATP for energy Bonds of ATP are broken to release energy Only 4-6 seconds worth of ATP is stored by muscles After this initial time, other pathways must be utilized to produce ATP

Energy for Muscle Contraction Direct phosphorylation Muscle cells contain creatine phosphate (CP) CP is a high-energy molecule After ATP is depleted, ADP is left CP transfers energy to ADP, to regenerate ATP CP supplies are exhausted in about 20 seconds

Energy for Muscle Contraction Aerobic Respiration Series of metabolic pathways that occur in the mitochondria Glucose is broken down to carbon dioxide and water, releasing energy This is a slower reaction that requires continuous oxygen

Energy for Muscle Contraction Anaerobic glycolysis Reaction that breaks down glucose without oxygen Glucose is broken down to pyruvic acid to produce some ATP Pyruvic acid is converted to lactic acid

Energy for Muscle Contraction Anaerobic glycolysis (continued) This reaction is not as efficient, but is fast Huge amounts of glucose are needed Lactic acid produces muscle fatigue

Muscle Fatigue and Oxygen Debt When a muscle is fatigued, it is unable to contract The common reason for muscle fatigue is oxygen debt Oxygen must be “repaid” to tissue to remove oxygen debt Oxygen is required to get rid of accumulated lactic acid Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less Slide 6.27 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Types of Muscle Contractions Isotonic contractions Myofilaments are able to slide past each other during contractions The muscle shortens Isometric contractions Tension in the muscles increases The muscle is unable to shorten Slide 6.28 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Muscle Tone Some fibers are contracted even in a relaxed muscle Different fibers contract at different times to provide muscle tone The process of stimulating various fibers is under involuntary control Slide 6.29 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Muscles and Body Movements Movement is attained due to a muscle moving an attached bone

Muscles and Body Movements Muscles are attached to at least two points Origin – attachment to a moveable bone Insertion – attachment to an immovable bone

Effects of Exercise on Muscle Results of increased muscle use Increase in muscle size Increase in muscle strength Increase in muscle efficiency Muscle becomes more fatigue resistant

Calcium Troponin-Tropomyosin Interaction

Results of actin-myosin interaction

Action Potentials on the Sarcolemma

Skeletal Muscles Responsible for movement of body and all of its joints Muscle contraction produces force that causes joint movement Muscles also provide protection posture and support produce a major portion of total body heat

Skeletal Muscles Over 600 skeletal muscles comprise approximately 40 to 50% of body weight 215 pairs of skeletal muscles usually work in cooperation with each other to perform opposite actions at the joints which they cross Aggregate muscle action - muscles work in groups rather than independently to achieve a given joint motion

Muscle Nomenclature Muscles are usually named due to visual appearance anatomical location function Shape – deltoid, rhomboid Size – gluteus maximus, teres minor Number of divisions – triceps brachii Direction of its fibers – external oblique

Muscle Nomenclature Location - rectus femoris, palmaris longus Points of attachment - coracobrachialis, extensor hallucis longus, flexor digitorum longus Action - erector spinae, supinator, extensor digiti minimi Action & shape – pronator quadratus

Muscle Nomenclature Action & size – adductor magnus Shape & location – serratus anterior Location & attachment – brachioradialis Location & number of divisions – biceps femoris

Shape of Muscles & Fiber Arrangement Cross section diameter factor in muscle’s ability to exert force greater cross section diameter = greater force exertion Muscle’s ability to shorten longer muscles can shorten through a greater range more effective in moving joints through large ranges of motion

Shape of Muscles & Fiber Arrangement 2 major types of fiber arrangements parallel & pennate each is further subdivided according to shape Parallel muscles fibers arranged parallel to length of muscle produce a greater range of movement than similar sized muscles with pennate arrangement

Fiber Arrangement - Parallel Categorized into following shapes Flat Fusiform Strap Radiate Sphincter or circular

Fiber Arrangement - Parallel Flat muscles usually thin & broad, originating from broad, fibrous, sheet-like aponeuroses allows them to spread their forces over a broad area Ex. rectus abdominus & external oblique

Fiber Arrangement - Parallel Fusiform muscles spindle-shaped with a central belly that tapers to tendons on each end allows them to focus their power onto small, bony targets Ex. brachialis, biceps brachii

Fiber Arrangement - Parallel Strap muscles more uniform in diameter with essentially all fibers arranged in a long parallel manner enables a focusing of power onto small, bony targets Ex. sartorius

Fiber Arrangement - Parallel Radiate muscles also described sometimes as being triangular, fan-shaped or convergent have combined arrangement of flat & fusiform originate on broad aponeuroses & converge onto a tendon Ex. pectoralis major, trapezius

Fiber Arrangement - Parallel Sphincter or circular muscles technically endless strap muscles surround openings & function to close them upon contraction Ex. orbicularis oris surrounding the mouth

Fiber Arrangement - Pennate Pennate muscles have shorter fibers arranged obliquely to their tendons in a manner similar to a feather arrangement increases the cross sectional area of the muscle, thereby increasing the power

Fiber Arrangement - Pennate Categorized based upon the exact arrangement between fibers & tendon Unipennate Bipennate Multipennate

Fiber Arrangement - Pennate Unipennate muscles fibers run obliquely from a tendon on one side only Ex. biceps femoris, extensor digitorum longus, tibialis posterior

Fiber Arrangement - Pennate Bipennate muscle fibers run obliquely on both sides from a central tendon Ex. rectus femoris, flexor hallucis longus

Fiber Arrangement - Pennate Multipennate muscles have several tendons with fibers running diagonally between them Ex. deltoid Bipennate & unipennate produce strongest contraction