muscles contraction and movement

1. Muscle Contraction and Movement
Muscles
Musclesare attachedto bonesbytendons
Musclesworkin antagonisticpairs
 Ex. Bicepsandtriceps
 One muscle contractswhile the otherrelaxes
Contractile apparatus
Skeletal muscle
 Muscle cell = muscle fiber
 Muscle fibersare made of myofibrils(striated)
 Myofibrilsare made of unitscalledsarcomeres
 Sarcomeresare made of thickand thinfilaments
 Z line isthe endof the sarcomere
 Thickand thinfilamentsslide overone anothertoshortenthe muscle
duringcontraction
The Thick Filament(Myosin)
Consistsof the proteincalledmyosin. A myosin
molecule isshapedabitlike agolf club,but
with2 heads. The headsstickoutto form the
cross bridge.Manyof these myosinmolecules
sticktogethertoform a thickfilament
Thin Filament(Actin)
The thinfilamentconsistsof a
proteincalledactin. The thin
filamentalsocontains tropomyosin.Thisproteinisinvolvedinthe
control of muscle contraction
Slidingfilamenttheory
 Linksthe structure of a sarcomere to itsfunction
 Duringcontractionthinfilamentsslide overthickfilaments
 Thickfilaments=myosinandhave “heads”
 Thinfilaments=actin,these slide
 Ca and ATPrequiredforslidingandattachment
 ATP bindstoa myosinhead,whichisreleasedfroman actin
filament
 Hydrolysisof ATPcocksthe myosinhead
 The myosinheadattachesto an actin bindingsite withthe
helpof Calcium
 The powerstroke slidesthe thinfilamentwhenADPandPi
are releasedfromit
 350 myosinheadsperthickfilament
 Can bind andunbindto thinfilamentupto5 timesper
second

2. Motor neurons and muscle contraction
Motor neuronsstimulate musclecontraction
Motor neuronsare branchedand can stimulate more thanone muscle
fiber
Motor unit= motor unitandall the muscle fibersitcontrols
Neuromuscularjunctions=the synapse betweenamotorneuronand a
muscle fiber
The strengthof a muscularcontractioniscontrolledbythe numberof
motor unitsactivated.More motorunits= strongercontractions
Musclesrequiringprecise control have one motorneuronpermuscle
fiber
Mechanismof stimulation:
An actionpotential releasesacetylcholine intothe
neuromuscularjunction
Acetylcholine depolarizesthe muscle cellchannelsinside onthe
sarcoplasmicreticulumreleaseCasoit can reach the
contractile apparatus
Mechanismof relaxation
Motor neuronstopsfiring
Ca pumpedbackintothe SR
Muscle injuries
The Injury: The term'pulledmuscle'comesfromthe descriptionof how the injurytakesplace.Usuallythe muscleis
forciblystretchedbeyonditslimitsandthe muscle tissue becomestorn.Dependinguponitsseverityitisclassifiedas
a first,secondor thirddegree strain:
 A firstdegree strainisdamage toa fewmuscle fibers.
 A seconddegree strainisdamage toa more extensive numberof muscle fibers.
 A thirddegree strainisa complete rupture of the muscle itself.
Signs and Symptoms Grade 1
Witha grade 1 the signsmay notbe presentuntil afterthe activityisover.There maybe asensationof cramp or
tightnessanda slightfeelingof painwhenthe musclesare stretchedorcontracted.
Grade 2
Witha grade 2 there isimmediate painwhichismore severe thanthe painof a grade one injury.Itis confirmedby
painon stretchand contractionof the muscle.A grade 2 isusuallysore totouch.
Grade 3
A grade 3 isa catastrophicinjury.There isanimmediate burningorstabbingpainandthe athlete isunable towalk.
The muscle iscompletelytornandthere maybe a large lumpof muscle tissue above adepressionwherethe tearis.