MICROSCOPICSKELETALMUSCLEANATOMY

HumanAnatomyUnit2

InAnatomyToday

SkeletalMuscleTissue

• Characteristics– Striated– Multinucleate– Voluntary(somatic)

• Anatomy–Muscle• Myofiber• Myofibril• Myofilament

MuscleMicroanatomy• Multinucleate

– Developfromthefusionofmultiplemyoblasts

– Eachmyoblasthasitsownnuclues

• Myofiber– Musclefiber– Musclecell

• Myofibril– Tubesofcontractileproteins

• Myofilament– Contractileproteins

MuscleFiber• Sarcolemma

– Membraneofmusclefiber– Electricallyexcitable– T-tubules

• Sarcoplasm– Musclecytoplasm

• Sarcoplasmicreticulum– ModifiedsmoothER– Lateralsacs– Storescalcium(Ca2+)

• Functionalunitofskeletalmuscleisthesarcomere

SarcomereStructure• Zline

– Definesthesarcomere• Aband

– Lengthofthickfilament• Hband

– Spacebetweenthinfilamentswithinasarcomere

• Iband– Spacebetweenthickfilaments

betweensarcomeres• Thickfilament• Thinfilament• Elasticfilament

ThinFilament

• 2strandsofactinmolecules– Hasbindingsitesfor

myosin

• Tropomyosin– Coversbindingsiteson

actinformyosin– Restingfiber

• Troponin– Holdstropomyosininplace– Bindstocalcium(Ca2+)

ThickandElasticFilament

• ThickFilament– Myosin– Tail– Myosinhead

• MyosinHead– 2bindingsites

• ADP+pi• Actin

• Elasticfilament– Titin– Achorsmyosininplacewithinsarcomere

MuscleContraction• Slidingfilamenttheory• Myosinheadsbindtoactin

– 6thinfilaments:1thickfilament

• Headschangeconformationandpulltheactinfilamentsacrossmyosinmolecule– Discontinuouspulling

• Sarcomereshortens– Thickandthinfilamentsdo

notshorten!• Allornoneresponse

NeuromuscularJunction

• Somaticmotorneuroninnervatesmusclefiber– Synapticbulb– Vesicles– Acetylcholine(ACh)

• Motorendplate– Invaginationofsarcolemma

– ReceptorsforACh• 1:1ratio

MotorUnit• Asinglemotorneuronand

allofthemusclefibersitinnervates

• Asomaticmotorneuronhascollateralbranchesthatinnervatemultiplemusclefibers

• Whenamotorneuronsendsasignaltocontract– Allfibersinthemotorunit

willcontract• Amusclewillbecomprised

ofmultiplemotorunits– Ratioofmotorunits:muscle

SkeletalMuscle

NeuromuscularJunction

CardiacMuscle

SmoothMuscle