Contractile mechanism of skeletal muscle 1

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Muscle Physiology

Prof. Dr. Rashid Mahmood

Contractile Mechanism of Skeletal Muscle I

Prof. Dr. Rashid MahmoodProf. Dr. Rashid Mahmood

Video of muscle contraction

Objectives Objectives Goal/Aim (Main Objective): To explain the mechanism of muscle contractionAt the end of this lecture students will be able toAt the end of this lecture students will be able to

Classify musclesDescribe organization of skeletal muscleDescribe general mechanism of skeletal muscle contraction.Describe molecular mechanism of skeletal muscle contraction.Outline different steps of Cross-bridge CycleExplain walk along theory...

Lesson contentsClassesClasses of Muscle of MusclePhysiological Anatomy Physiological Anatomy of Skeletal Muscleof Skeletal Muscle

SarcomereSarcomereActin & Myosin FilamentsActin & Myosin FilamentsThe T Tubules and Sarcoplasmic ReticulumThe T Tubules and Sarcoplasmic Reticulum

Sequence of events in Sequence of events in neuromuscular neuromuscular transmissiontransmissionSynthesis & Release of Synthesis & Release of Acetylcholine Acetylcholine Steps of Steps of General mechanism of muscle General mechanism of muscle contraction contraction

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Three Classes of Three Classes of MuscleMuscleBased on histological appearance and functionBased on histological appearance and function

SkeletalSkeletalstriated, voluntarystriated, voluntary

CardiacCardiacstriated, involuntarystriated, involuntary

SmoothSmoothnonstriated, involuntarynonstriated, involuntary

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Muscle

Tendon


Skeletal Muscle

Physiological Physiological Anatomy of Anatomy of

Muscle Muscle


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Subunits Subunits Muscle

Muscle Fiber

Myofibrils

Myosin Filaments

Actin Filaments

Muscle fasciculus


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Light and Dark bandsLight and Dark bands

Striated Muscle


Assessment Q. 1Assessment Q. 1Name the THREE types of Muscle Name the THREE types of Muscle


Sarcomere Sarcomere


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Actin + Myosin Actin + Myosin FilamentsFilaments

Cross- Bridges

Sarcomere


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SarcomeSarcomerere


Proteins that help in Proteins that help in alignment of Myofibrilsalignment of Myofibrils


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Myosin Molecule Myosin Molecule


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Myosin filamentMyosin filamentArm


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Myosin Molecule & Myosin Molecule & filamentfilament


Assessment Q. 2Assessment Q. 2Name any THREE parts of Myosin Name any THREE parts of Myosin FilamentFilament


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Actin filament Actin filament


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Actin HelixActin Helix+ +

tropomyositropomyosinn

+troponin+troponin= =

Actin Actin FilamentFilament


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Troponin complex Troponin complex


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Binding Binding of of

myosin myosin head head with with

active active site in site in

the the presencpresence of Ca+e of Ca+

++


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Mammalian Skeletal Muscle: Two Transverse

Tubules per Sarcomere

Z lineProf. Dr. Rashid MahmoodProf. Dr. Rashid Mahmood

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The T Tubules and Sarcoplasmic The T Tubules and Sarcoplasmic ReticulumReticulum


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Relation between T Tubules Relation between T Tubules and Sarcoplasmic Reticulumand Sarcoplasmic Reticulum

Sarcoplasmic Reticulum=Sarcoplasmic Reticulum=Terminal Cisternae+Terminal Cisternae+

Long Longitudinal Tubules Long Longitudinal Tubules

Terminal CisternaeTerminal Cisternae Long Longitudinal TubulesLong Longitudinal Tubules

•T TubuleT Tubule


Assessment Q. 3Assessment Q. 3Name the THREE parts of Actin Name the THREE parts of Actin Filament Filament


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StepsSteps of of General General

mechanismmechanism of of muscle muscle

contraction contraction


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Sequence of events in Sequence of events in neuromuscular neuromuscular transmissiontransmission


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Synthesis & Release of Synthesis & Release of Acetylcholine Acetylcholine


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StepsSteps of General of General mechanismmechanism of of muscle contractionmuscle contraction


AP= Action PotentialMF= muscle fiber NMJ= Neuromuscular Junction Ach= acetylcholineSR= sarcoplasmic reticulum

Events occurring at NMJEvents occurring at NMJ


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StepsSteps of of General General

mechanismmechanism of of muscle muscle

contractioncontraction


Summary of StepsSummary of Steps of General of General mechanismmechanism of muscle of muscle contractioncontraction


Summary of Events Summary of Events of muscle of muscle contractioncontraction


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Take Home PointsTake Home PointsThree Classes of Muscle Three Classes of Muscle are Skeletal, Cardiac, & Smooth. are Skeletal, Cardiac, & Smooth. Functional unit of Muscles is muscle fibre, composed of many Functional unit of Muscles is muscle fibre, composed of many myofibrilsmyofibrils. Each . Each

myofibril is composed of myofibril is composed of myofilamentsmyofilaments: : actinactin & & myosinmyosin..A A Sequence of eventSequence of events occurs at s occurs at neuromuscular junctioneuromuscular junction that finally results in n that finally results in

muscle contractionmuscle contractionAn An Action potential Action potential reaches reaches nerve fiber endingnerve fiber ending at neuromuscular junction, at neuromuscular junction,

causing causing release of acetylcholinerelease of acetylcholineAcetylcholine binds with its receptors at Acetylcholine binds with its receptors at motor-end platemotor-end plate, resulting in opening of , resulting in opening of

“acetylcholine-gated Sodium channels“acetylcholine-gated Sodium channels””Diffusion of Na+ into muscle fiber Diffusion of Na+ into muscle fiber causes action potential in muscle fibercauses action potential in muscle fiberAction potential spreads in muscle fiber through Action potential spreads in muscle fiber through T-Tubule system, that T-Tubule system, that causes causes

release of stored calcium ions from release of stored calcium ions from sarcoplasmic reticulum sarcoplasmic reticulum Ca++ ions initiate Ca++ ions initiate attractive forces attractive forces between actin and myosin filaments causing between actin and myosin filaments causing

sliding of actin over myosin sliding of actin over myosin (Sliding Filament Mechanism)(Sliding Filament Mechanism)The The cross-bridge cycle cross-bridge cycle is repeated again & again till the completion of contraction is repeated again & again till the completion of contraction Sliding of actin filaments over myosin filaments through cross-bridge cycle is Sliding of actin filaments over myosin filaments through cross-bridge cycle is

explained by explained by Walk-Along Theory (or Ratchet Theory)Walk-Along Theory (or Ratchet Theory)

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Assessment Q. 4Assessment Q. 4Name that current theory that Name that current theory that explains Sliding of actin filaments explains Sliding of actin filaments over myosin filaments through over myosin filaments through cross-bridge cyclecross-bridge cycle


Learning ResourcesLearning ResourcesGuyton and Hall (Text book of physiology), Guyton and Hall (Text book of physiology), 13th Edition13th EditionGanong (Text book of physiology), 24th Ganong (Text book of physiology), 24th EditionEditionHuman Physiology : from cells to system Human Physiology : from cells to system Lauralee Sherwood,9Lauralee Sherwood,9thth Edition Edition Human Physiology Stuart Ira Fox, 13th Human Physiology Stuart Ira Fox, 13th EditionEditionInternetInternet

Prof. Dr. Rashid MahmoodProf. Dr. Rashid Mahmood3737

Next topicContractile Mechanism of Skeletal Muscle II14/1/2017, 0930 am: 1030 amPrior knowledge required: Contractile Mechanism of Skeletal Muscle I


ANY QUESTIONS?Prof. Dr. Rashid MahmoodProf. Dr. Rashid Mahmood3939

Health & Medicine

Contractile mechanism of skeletal muscle 1