Chapter 4: Skeletal Muscle System - PowerPoint Presentation

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Chapter 4: Skeletal Muscle SystemSlide2

Learning Objectives

Describe the

anatomy and physiology of skeletal muscleRole of muscle fiber types as it relates to different types of athletic performancesHistochemical techniques for identification of muscle fiber typesExplain how skeletal muscle produces movementBasis of proprioception in muscle and kinesthetic senseForce production capabilities of muscle and types of muscle actionsTraining-related changes in skeletal muscleEffects of simultaneous high intensity endurance and strength training on adaptations

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Basic Structure of Skeletal Muscle

Basic Organization of Skeletal

Muscle3Slide4

Basic Structure of Skeletal Muscle (continued)

Connective Tissue (CT) and Muscle Organization

Tendons: bands of tough, fibrous CT that connect muscle to boneFasciculus: small bundle of muscle fibersMuscle fiber: long, multinucleated cell that generates force when stimulatedMyofibril: portion of muscle composed of thin & thick myofilaments (actin & myosin)Actin & myosin: contractile proteins in muscle4Slide5

Basic Structure of Skeletal Muscle (continued)

Connective Tissue (CT) and Muscle Organization (cont’d)

Role of CTStabilizes & supports components of skeletal muscleSurrounds muscle at each organizational level3 layers of CT in muscleEpimysium: covers whole musclePerimysium: covers bundles of muscle fibers (fasciculi)Endomysium: covers individual muscle fibers5Slide6

Basic Structure of Skeletal Muscle (continued)

Connective Tissue

in Skeletal Muscle6Slide7

Basic Structure of Skeletal Muscle (continued)

Characteristics of Connective Tissue

Sheaths coalesce to form tendons at each end of muscleForce generated by muscle is transferred to tendon & boneEpimysium helps prevent spread of signal for muscle activationElastic component of CT contributes to:Force & power production (like recoil of rubber band)Stretch-shortening cycleEccentric action (elongation)Concentric action (shortening)7Slide8

Basic Structure of Skeletal Muscle (continued)

The Sarcomere

Basic skeletal muscle unit Capable of force production & shorteningArrangement of protein filaments gives striated appearanceComponentsZ lines: at each end of sarcomereH zone: in middle of sarcomere, contains myosinI bands: at edges of sarcomere, contain actinA band: overlapping actin & myosinM line: middle of H zone, holds myosin in place8Slide9

Basic Structure of Skeletal Muscle (continued)

The Sarcomere

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Basic Structure of Skeletal Muscle (continued)

Actions of Sarcomere

As sarcomere shortens:Actin filaments slide over myosinH zone disappears as actin filaments slide into itI bands shorten as actin & myosin slide over each otherZ lines approach ends of myosin filamentsAs sarcomere relaxes:It returns to original lengthH zone & I bands return to original size & appearanceLess overlap between actin & myosin10Slide11

Basic Structure of Skeletal Muscle (continued)

Noncontractile

ProteinsProvide lattice work for positioning of actin & myosinContribute to elastic component of muscle fiberTitinConnects Z line to M lineStabilizes myosin in longitudinal axisLimits ROM of sarcomere & contributes to passive stiffnessNebulinExtends from Z line & is localized to I bandStabilizes actin by binding with actin monomers11Slide12

Basic Structure of Skeletal Muscle (continued)

Noncontractile

Proteins12Slide13

Basic Structure of Skeletal Muscle (continued)

Actin (Thin) Filament

2 intertwined helices of actin moleculesProjects from Z lines toward middle of sarcomereActive site: where heads of myosin crossbridges bind to actinWrapped by tropomyosin & troponin (regulatory protein molecules)Subunits of troponinTroponin I: holds to actinTroponin T: holds to tropomyosinTroponin C: can bind calcium

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Basic Structure of Skeletal Muscle (continued)

Actin

Filament Organization14Slide15

Basic Structure of Skeletal Muscle (continued)

Myosin Filament

Has globular head, hinged pivot point, & fibrous tailHeads: made up of enzyme myosin ATPaseTails: intertwine to form myosin filamentCrossbridgeConsists of 2 myosin molecules, with 2 headsInteracts with actinDevelops force to pull actin over myosinFeatures different isoforms of ATPase15Slide16

Basic Structure of Skeletal Muscle (continued)

Myosin Filament

Organization16Slide17

Basic Structure of Skeletal Muscle (continued)

Muscle Fiber Types

Type I (slow-twitch)Slow to reach peak force productionLow peak forceHigh capacity for oxidative metabolismFatigue-resistantEndurance performance17Slide18

Basic Structure of Skeletal Muscle (continued)

Muscle Fiber Types (cont’d)

Type II (fast-twitch)Rapidly develop forceHigh peak forceLow capacity for oxidative metabolismFatigue easilySprint, short-term performance18Slide19

Basic Structure of Skeletal Muscle (continued)

Muscle

Fiber Types Compared19Slide20

Basic Structure of Skeletal Muscle (continued)

Myosin ATPase Histochemical Analysis

Differentiates among muscle fiber subtypesInvolves histochemical staining procedureProcessThin cross-section of muscle is obtained from biopsy sampleSample is placed into baths of different pH conditionsFibers are classified according to staining intensitySubtypes, from most oxidative (slowest) to least (fastest):I, IC, IIC, IIAC, IIA, IIAX, IIX20Slide21

Basic Structure of Skeletal Muscle (continued)

Myosin ATPase

Delineation of Muscle Fiber Types21Slide22

Basic Structure of Skeletal Muscle (continued)

Myosin Heavy Chain (MHC)

Molecular weight of 230 kDAssociated with 2 light chains (per MHC)EssentialRegulatoryMHC composition of muscle can profile fiber type compositionHigh correlation between subtypes I, IIA, & IIX and MHC subtypes I, Ia, & Ix, respectively22Slide23

Basic Structure of Skeletal Muscle (continued)

Myosin

Molecule23Slide24

Sliding Filament Theory

Overview

Explains how muscle proteins interact to generate forceProposed in 1954SummaryActin & myosin filaments slide over each other to produce force without the filaments themselves changing lengthSliding of actin over myosin produces change in striation pattern# of actomyosin complexes formed dictates how much force is produced24Slide25

Sliding Filament Theory (continued)

Steps Mediating the Contraction Process

Electrical impulse is generated at neuromuscular junctionImpulse spreads across sarcolemma into T-tubulesRyanodine receptors release Ca++ into cytosol of muscle fiberCa++ binds to troponin C subunitTropomyosin uncovers active sites of actinMyosin crossbridge heads bind actin, form actomyosin complexHeads pull actin toward center of sarcomere (power stroke)

Force is produced

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Sliding Filament Theory (continued)

Sarcoplasmic Reticulum

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Sliding Filament Theory (continued)

Ratchet Movement Produces Power Stroke

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Sliding Filament Theory (continued)

Muscle Contraction Steps

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Proprioception and Kinesthetic Sense

Proprioception

How the body senses where it is in spaceMonitored by feedback as to length of muscle & force producedProprioceptors: receptors located in muscles and tendonsInfo. from proprioceptors is sent to brain (conscious & subcon.)Learning effectAbility to repeat a specific motor unit recruitment patternResults in successful performance of a skillRequires practice29Slide30

Proprioception and Kinesthetic Sense (continued)

Muscle Spindles

Proprioceptors in skeletal muscle2 functionsMonitor stretch or length of muscleInitiate a contraction when muscle is stretchedStretch reflex: quickly stretched muscle initiates immediate contraction due to being stretchedLocated in intrafusal fibers (modified muscle fibers)30Slide31

Proprioception and Kinesthetic Sense (continued)

Muscle

Spindles31Slide32

Proprioception and Kinesthetic Sense (continued)

Golgi Tendon Organs

Proprioceptors in tendonMain function is to monitor & respond to tension in tendonActivated by excessive force on tendonInhibit action of muscle to prevent injuryNew training techniques seek to decrease inhibition by Golgi tendon organs to allow greater force production32Slide33

Proprioception and Kinesthetic Sense (continued)

Golgi Tendon Organs

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Force Production Capabilities

Types of Muscle Actions

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Force Production Capabilities (continued)

Terms Used to Describe Resistance Exercise

Isotonic: muscle generates same force throughout ROMDynamic constant external resistance: resistance provided by free weights or weight machine that remains constantIsoinertial: exercise movement with variable velocity & constant resistance throughout ROMVariable resistance: resistance that changes over ROMIsokinetic: resistance in which velocity of limb’s movement throughout ROM is held constant by a device35Slide36

Force Production Capabilities (continued)

Force-Velocity Curve

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Force Production Capabilities (continued)

Training Effects on Concentric Force-Velocity Curve

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Force Production Capabilities (continued)

Strength Curves

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Force Production Capabilities (continued)

Length-Tension Relationship

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Force Production Capabilities (continued)

Force-Time Curve

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Muscle Adaptations that Improve Performance

Effects of Endurance Training

Increase in delivery of oxygen to muscle, caused by:Increase in # of capillaries per muscle fiberIncrease in capillary densityIncrease in concentration of myoglobin, which increases rate of oxygen transport from capillaries to mitochondriaEnhanced ability for aerobic metabolism, caused by:Increase in size & number of mitochondria in muscleIncrease in ability to produce ATP41Slide42

Effects of Resistance Training

Hypertrophy

Increase in size of muscle fibersResults from addition of protein & new myofibrils to existing fibers, making them largerRequires addition of myonuclei to support increase in muscle fiber sizeHyperplasiaIncrease in number of muscle fibersOccurrence is controversial42

Muscle Adaptations that Improve Performance (continued)Slide43

Compatibility of Exercise Training Programs

Conclusions from studies of concurrent endurance & resistance training:

Strength can be compromised due to endurance trainingPower may be compromised more than strengthAnaerobic performance may be decreased due to endurance trainingDevelopment of maximal oxygen consumption is not compromisedEndurance capabilities are not diminished by strength training43Muscle Adaptations that Improve Performance (continued)