The Muscular System. Muscular System Functions MOVEMENT MOVEMENT Maintain Posture Maintain Posture Stabilize Joints Stabilize Joints Generate HEAT Generate.
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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
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