The Muscular SystemThe Muscular System

           

           

Muscular System FunctionsMuscular System Functions

MOVEMENTMOVEMENT Maintain PostureMaintain Posture Stabilize JointsStabilize Joints Generate HEATGenerate HEAT

– 40% body mass40% body mass– 80% body heat 80% body heat – Endothermy!Endothermy!

Muscle TissueMuscle Tissue

Tissue Review: Tissue Review: – CardiacCardiac Cardiovascular System Cardiovascular System

Involuntary, StriatedInvoluntary, Striated

– Smooth Smooth Cardiovascular, Digestive, Cardiovascular, Digestive, Reproductive, etc. Reproductive, etc.

Involuntary, non-striatedInvoluntary, non-striated

– Skeletal*Skeletal* MUSCULAR SYSTEM MUSCULAR SYSTEM Voluntary, striatedVoluntary, striated

Muscles are…Muscles are…

Excitable (irritable)Excitable (irritable) ContractileContractile ExtensibleExtensible ElasticElastic Myo-, Mys, SarcoMyo-, Mys, Sarco- (muscle prefixes)- (muscle prefixes)

Skeletal Muscle TissueSkeletal Muscle Tissue

MUSCLE CELL STRUCTUREMUSCLE CELL STRUCTURE– Arrangement: large, long FIBERSArrangement: large, long FIBERS

Fiber = muscle cellFiber = muscle cell

– Two major protein filaments present:Two major protein filaments present: ActinActin Myosin myofilamentsMyosin myofilaments

Skeletal Muscle StructureSkeletal Muscle Structure

StriatedStriated– Due to actin/myosinDue to actin/myosin

ElongatedElongated– Varied lengthsVaried lengths

Multinucleated Multinucleated

TEXT:TEXT: Structures / Regions to know:Structures / Regions to know:

– MuscleMuscle– TendonTendon– EpimysiumEpimysium– FacsicleFacsicle– Muscle FiberMuscle Fiber– PerimysiumPerimysium– MyofibrilMyofibril– EndomysiumEndomysium

Muscle AnatomyMuscle Anatomy

http://www.http://www.bmbbmb..psupsu..eduedu/courses/bisci004a/muscle/b4muscle./courses/bisci004a/muscle/b4muscle.htmhtm

Skeletal Muscle ConnectionsSkeletal Muscle Connections

Direct connection to BoneDirect connection to Bone Indirect connection via TENDONIndirect connection via TENDON ORIGINORIGIN: bone that does NOT move : bone that does NOT move

when muscle contractswhen muscle contracts IINSERTIONNSERTION: bone that MOVES when : bone that MOVES when

muscle contractsmuscle contracts

Microscopic Structure ofMicroscopic Structure of Muscle Fiber Muscle Fiber

Cell membrane = Cell membrane = SarcolemmaSarcolemma Cytoplasm = Cytoplasm = SarcoplasmSarcoplasm Multiple Mitochondria = High E outputMultiple Mitochondria = High E output Fiber is filled with long myofibrilsFiber is filled with long myofibrils Myofibrils filled with filaments arranged Myofibrils filled with filaments arranged

in contractile units called in contractile units called SARCOMERESSARCOMERES..– MyosinMyosin (thick filament) (thick filament)– Actin Actin (thin filament)(thin filament)

Sarcoplasmic ReticulumSarcoplasmic Reticulum

Specialized ER connected to cell Specialized ER connected to cell surface by surface by T-tubulesT-tubules

Surrounds each myofibril Surrounds each myofibril At rest, filled with Ca++ maintained At rest, filled with Ca++ maintained

by a calcium “pump”, uses ATP by a calcium “pump”, uses ATP When activatedWhen activated, pores open and , pores open and

release calcium, initiating contractionrelease calcium, initiating contraction

Actin (thin) filamentActin (thin) filamentCompositionComposition

Long chains of actin globules in Long chains of actin globules in double spiral arrangementdouble spiral arrangement

Each actin contains binding site for Each actin contains binding site for myosinmyosin

Tropomyosin spiral around chainTropomyosin spiral around chain– blocks active site on actinblocks active site on actin

Troponin clustered along spiral Troponin clustered along spiral – Binding site for calcium!Binding site for calcium!

Actin FilamentActin Filament

Myosin (thick) filamentMyosin (thick) filamentCompositionComposition

Contains 2 tails each with globular Contains 2 tails each with globular heads heads

Heads have ATP binding sites and Heads have ATP binding sites and ATPase for splitting ATP ATPase for splitting ATP

Heads attracted to active sites on Heads attracted to active sites on actin molecules actin molecules

Heads form cross-bridges with actinHeads form cross-bridges with actin

Myosin FilamentMyosin Filament

Multiple Myosin FilamentsMultiple Myosin Filaments

Sarcomere structureSarcomere structure

Alternating dark and light bands Alternating dark and light bands Central Central H-zoneH-zone contains MYOSIN only contains MYOSIN only Lateral Lateral A-bands A-bands contain both contain both

ACTIN and MYOSIN filaments ACTIN and MYOSIN filaments End in End in I-bandsI-bands contain ACTIN onlycontain ACTIN only

(with (with Z-lineZ-line in center) in center)

Z LINE TO Z LINE = 1 SARCOMEREZ LINE TO Z LINE = 1 SARCOMERE

SARCOMERE STRUCTURE

Sarcomere Sarcomere

Nerve supplyNerve supplyto Muscle Fiberto Muscle Fiber

Each muscle fiber served by a motor Each muscle fiber served by a motor neuronneuron

Motor neuron ends in a pad filled Motor neuron ends in a pad filled with vacuoles packed with with vacuoles packed with neurotransmitter neurotransmitter

Pad sits above specialized piece of Pad sits above specialized piece of sarcolemma called sarcolemma called motor end platemotor end plate

Neuron pad + motor end plate Neuron pad + motor end plate ==

NeuromusculNeuromuscular junction ar junction (Space between called synaptic

cleft )

Sliding Filament Theory ofSliding Filament Theory of Muscle Contraction Muscle Contraction

Sequence of Steps:Sequence of Steps:

1.1. Neuron releases neurotransmitter, Neuron releases neurotransmitter, acetylcholineacetylcholine (ACh) into synaptic cleft (ACh) into synaptic cleft

2.2. ACh diffuses to motor end plate ACh diffuses to motor end plate

3.3. ACh binds to receptor on motor end ACh binds to receptor on motor end plateplate

4.4. Gated channel protein opens, Na+ Gated channel protein opens, Na+ rushes into cell interior, upsets RMP!rushes into cell interior, upsets RMP!

Generation ofGeneration ofAction PotentialAction Potential

RMP = -70 MvRMP = -70 Mv Sudden influx of Na+ generates Sudden influx of Na+ generates

Action PotentialAction Potential RMP later restored to normal byRMP later restored to normal by

sodium-potassium pumpsodium-potassium pump

5. Action potential carried along the 5. Action potential carried along the sarcolemma to transverse (“T”) sarcolemma to transverse (“T”) tubules connected to Sarcoplasmic tubules connected to Sarcoplasmic Reticulum Reticulum

6.6. SR membrane becomes permeable SR membrane becomes permeable to calciumto calcium

7.7. Sarcoplasm is flooded with calcium Sarcoplasm is flooded with calcium ionsions

8. Ca++ binds to troponin8. Ca++ binds to troponin

9. Ca/Troponin pulls tropomyosin out 9. Ca/Troponin pulls tropomyosin out of the way, unmasks active site on of the way, unmasks active site on actin molecules actin molecules

10. Myosin heads attach to actin 10. Myosin heads attach to actin

11. Heads rotate, pull actin in to H-11. Heads rotate, pull actin in to H-zone zone

12. Z lines get closer…12. Z lines get closer…

13. Myosin splits ATP to recharge 13. Myosin splits ATP to recharge

14. Continues until Action Potential is 14. Continues until Action Potential is restored and Ca++ is pumped back restored and Ca++ is pumped back into SR into SR

15.All sarcomeres shorten, shortening 15.All sarcomeres shorten, shortening muscle cellmuscle cell

16. Shortening cell pulls on tendons 16. Shortening cell pulls on tendons attached to bones, moving bone at attached to bones, moving bone at articulation articulation

17. Contraction of opposite muscle 17. Contraction of opposite muscle required to fully elongate shortened required to fully elongate shortened musclemuscle

Reminders:Reminders:

Refractory PeriodRefractory Period All or None EffectAll or None Effect Breakdown of ACh by ACh-esterase Breakdown of ACh by ACh-esterase

Disorders/Conditions of the Disorders/Conditions of the Muscular SystemMuscular System

Duchenne’s Muscular DystrophyDuchenne’s Muscular Dystrophy– Sex linked inheritanceSex linked inheritance– Dystrophin Dystrophin protein deficiency protein deficiency – Tearing of sarcolemmaTearing of sarcolemma– Accumulation of CT/fatAccumulation of CT/fat– Muscular ATROPHYMuscular ATROPHY

TetanusTetanus