Chapter 11 the Muscular System - Sp10

8/16/2019 Chapter 11 the Muscular System - Sp10

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Illinois State University

Chapter 11:

The Muscular System

The Motors of the Body


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Behavioral Properties of

the Musculotendinous Unit The characteristic behavioralproperties of muscle are:

extensibilityelasticity

irritability

and the ability to develop tension.


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the Musculotendinous Unit !xtensibility " the ability to bestretched or to increase in length.

!lasticity " the ability to return tonormal length after extension or

contraction.


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the Musculotendinous Unit Parallel elastic component " musclemembranes that provide resistivetension #hen a muscle is passively

stretched.

Series elastic component " tendons that

act as a spring to store elastic energy#hen an active muscle is stretched.


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Series and parallel elastic elements in muscle.A.Resting muscle contains elastic elements in series with the contractile

elements (sarcomeres) and in parallel with them.B.During an isometric contraction, the muscle does not change length,but sarcomeres shorten, stretching the series elastic elements.C.During isotonic contraction, the contractile elements shorten,stretching the series elastic elements, before they deelop tension to liftthe load.D.!uscle begins to shorten when contractile elements shorten further.


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the Musculotendinous Unit Both the P!$ and S!$ have aviscous property that enablesmuscle to stretch and recoil in atime"dependent fashion.




the Musculotendinous Unit %hen a static stretch of a musclegroup such as the hamstrings ismaintained over a period of timethe muscle progressivelylengthens increasing &oint range ofmotion.




the Musculotendinous Unit 'i(e#ise after a muscle group hasbeen stretched it does not recoil toresting length immediately butshortens gradually over a period oftime.

This viscoelastic response of muscleis independent of gender.




the Musculotendinous Unit Irritability " the ability to respondto a stimulus.

Stimuli a)ecting muscles are eitherelectrochemical such as an actionpotential from the attaching nerve ormechanical such as an external blo#

to a portion of a muscle.




the Musculotendinous Unit If the stimulus is of su*cientmagnitude muscle responds bydeveloping tension.

$ontractility " the ability of a

muscle to shorten in length.



Muscle Contraction

%hen a muscle contracts it pulls#ith e+ual force on eachattachment.



Muscle Contraction

, muscle-s line of pull refers to thedirection of the resultant forceproduced at an attachment.


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S(eletal Muscle unction

The magnitude of the tor+uegenerated is the product of theforce developed by the muscle andthe perpendicular distance of theline of action of that force from thecenter of rotation at the &oint.


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In (eeping #ith the la#s of vectoraddition the net tor+ue present atthat &oint determines the directionof any resulting movement.


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The #eight of the attached bodysegment external forces acting onthe body and tension in anymuscle crossing a &oint can allgenerate tor+ues at that &oint.


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$oncentric muscle action " #hen amuscle shortens under tension.

!ccentric muscle action " #hen amuscle lengthens under tension.

Isometric muscle action " #hen a

muscle produces tension but thereis not movement.


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,gonist " a muscle that causesmovement. The prime mover.

,ntagonist " a muscle that resistsmovement.

Synergist " a muscle that assists

the agonist in performing amovement.


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Stabili/er 0eutrali/er ixator " roleplayed by a muscle acting tostabili/e a body part against someother force or eliminate anun#anted action produced by anagonist.

T#o &oint muscles " muscles #hichcross t#o &oints.


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They can fail to produce force#hen slac( 1active insu*ciency2and can restrict range of motion#hen fully stretched 1passiveinsu*ciency2.


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unctional 3rgani/ation ofS(eletal Muscle: Muscle 4bers " s(eletal muscle

4bers gro# in length and diameterfrom birth to adulthood #ith a4vefold increase in 4ber diameterduring this period.

iber diameter can also beincreased by resistance training.


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unctional 3rgani/ation ofS(eletal Muscle: The number of muscle 4bers

present is genetically determinedand varies from person to person.


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unctional 3rgani/ation ofS(eletal Muscle: Summation " progressively additive

e)ect of repeated stimuli.

Tetanus " state of muscleproducing sustained maximal

tension resulting from repetitivestimulation.


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unctional 3rgani/ation ofS(eletal Muscle: Motor units " a single motor neuron

and all 4bers it innervates.iber types.

5ecruitment of motor units " slo#t#itch motor units al#ays producetension 4rst #hether the 4nalmovement is slo# or fast.


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iber architecture:

Parallel 4ber arrangement " 4bers arealongside each other.

Pennate 4ber arrangement " arro#. The tibialis posterior rectus femoris

and deltoid muscles are pennate.


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Parallel Muscle Fibers


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Pennate Fibers


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iber architecture:

%hen tension is developed in aparallel"4ber muscle anyshortening of the muscle isprimarily the result of theshortening of the 4bers.


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iber architecture:

%hen the 4bers of a pennatemuscle shorten the rotate abouttheir tendon attachmentsprogressively increasing the angleof pennation.


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iber architecture:

Pennate 4ber arrangementspromote muscle force productionand parallel 4ber arrangementsfacilitate muscle shortening.


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iber architecture:

,lthough pennation reduces thee)ective force generated at agiven level of 4ber tension thisarrangement allo#s the pac(ing ofmore 4bers than the amount thatcan be pac(ed into a longitudinal

muscle occupying e+ual space.


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iber architecture:

Because pennate muscles containmore 4bers per unit of musclevolume they can generate moreforce than parallel 4bered musclesof the same si/e.


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Mechanical actors,)ecting Muscular orce The magnitude of the force

generated by muscle is alsorelated to:the velocity of muscle shortening

the length of the muscle #hen it isstimulated

and the period of time since themuscle received a stimulus.


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Mechanical actors,)ecting Muscular orce The relationship bet#een the

concentric force exerted by amuscle and the velocity at #hichthe muscle is capable ofshortening is inverse.


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Mechanical actors,)ecting Muscular orce %hen a muscle develops

concentric tension against a highload the velocity of muscleshortening must be relatively slo#.


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Mechanical actors,)ecting Muscular orce %hen resistance is lo# the

velocity of shortening can berelatively fast.


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Mechanical actors,)ecting Muscular orce The stronger a muscle the greater

the magnitude of its isometricmaximum on the force"velocitycurve.


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Mechanical actors,)ecting Muscular orce !ccentric strength training involves

the use of resistance that isgreater than the athlete6smaximum isometric forcegenerating capabilities.


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Mechanical actors,)ecting Muscular orce !ccentric training is also

associated #ith increased musclesoreness.


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orce"'ength 5elationship:

In single muscle 4bers and isolatedmuscle preparations forcegeneration is at its pea( #hen themuscle is at normal resting length1neither stretched nor contracted2.


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orce"'ength relationship:

%hen the length of the muscleincreases or decreases beyondresting length the maximum forcethe muscle can produce decreasesfollo#ing the form of a bell"shapedcurve.


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Length-Tension elationship

!sarcomere only"


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Length-Tension elationship

!sarcomere # elastic

component"Rapid

stretch of

muscle

increasesforce

during

ensuing

concentric phase

SSCElastic component

Stretch reflex


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%ithin the human body ho#everforce generation capabilityincreases #hen the muscle isslightly stretched.


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Parallel"4ber muscles producemaximum tensions at &ust overresting length and pennate 4bermuscles generate maximumtensions at bet#een 789 and7;9 of resting length.


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This phenomenon is due to thecontribution of the elasticcomponents of muscle 1primarilythe S!$2 #hich add to the tensionpresent in the muscle #hen themuscle is stretched.


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%hen a muscle is activelystretched the S!$ causes anelastic recoil e)ect and the stretchre


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This pattern of eccentriccontraction follo#ed immediatelyby concentric contraction is (no#nas the stretch"shortening cycle.


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orce"Time relationship:

%hen a muscle is stimulated abrief period of time elapses beforethe muscle begins to developtension.

5eferred to as electromechanical

delay.


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Muscular strength is mostcommonly measured as theamount of tor+ue a muscle groupcan generate at a &oint.


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The tension"generating capabilityof a muscle is related to its cross"sectional area and training state.


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%ith both concentric and eccentricstrength training gains in strengthover at least the 4rst 78 #ee(sappear to be related to factorssuch as improved innervation ofthe trained muscle rather than to

the increase in its cross"sectionalarea.


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Muscular po#er " the product offorce and velocity.

Maximum po#er occurs atapproximately one"third ofmaximum velocity and at

approximately one"third ofmaximum concentric force.


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Muscular endurance " the ability ofthe muscle to exert tension over aperiod of time.


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Muscle Force

!)ect of muscle temperature " asbody temperature elevates thespeeds of nerve and musclefunctions increase.

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Chapter 11 the Muscular System - Sp10