the muscular system alireza ashraf, m.d. professor of physical medicine & rehabilitation shiraz...

The Muscular SystemThe Muscular System

Alireza Ashraf, M.D.Professor of Physical Medicine & Rehabilitation

Shiraz Medical school

The Muscular SystemThe Muscular SystemMuscles are responsible Muscles are responsible

for all types of body for all types of body movementmovement

Three basic muscle Three basic muscle types are found in the types are found in the bodybody

–Skeletal muscleSkeletal muscle–Cardiac muscleCardiac muscle–Smooth muscleSmooth muscle

Characteristics of MusclesCharacteristics of Muscles Muscle cells are elongated Muscle cells are elongated

(muscle cell = muscle fiber)(muscle cell = muscle fiber) Contraction of muscles is Contraction of muscles is

due to the movement of due to the movement of microfilamentsmicrofilaments

All muscles share some All muscles share some terminologyterminology– Prefix Prefix myomyo refers to muscle refers to muscle– Prefix Prefix mysmys refers to muscle refers to muscle– Prefix Prefix sarcosarco refers to flesh refers to flesh

Skeletal Muscle CharacteristicsSkeletal Muscle Characteristics Most are Most are

attached by attached by tendons to tendons to bonesbones

Skeletal Muscle Skeletal Muscle CharacteristicsCharacteristics

Cells are multinucleateCells are multinucleate StriatedStriated – have visible banding – have visible banding VoluntaryVoluntary – subject to conscious control – subject to conscious control Cells are surrounded and bundled by Cells are surrounded and bundled by

connective tissueconnective tissue

Connective Tissue Wrappings Connective Tissue Wrappings of Skeletal Muscleof Skeletal Muscle

Endomysium – Endomysium – around single around single muscle fibermuscle fiber

Perimysium – Perimysium – around a around a fascicle fascicle (bundle) of (bundle) of fibersfibers

Connective Tissue Wrappings Connective Tissue Wrappings of Skeletal Muscleof Skeletal Muscle

Epimysium – Epimysium – covers the covers the entire skeletal entire skeletal musclemuscle

Fascia – on the Fascia – on the outside of the outside of the epimysiumepimysium

Skeletal Muscle AttachmentsSkeletal Muscle Attachments Epimysium blends into a Epimysium blends into a

connective tissue connective tissue attachmentattachment– Tendon – cord-like structureTendon – cord-like structure– Aponeuroses – sheet-like Aponeuroses – sheet-like

structurestructure Sites of muscle Sites of muscle

attachmentattachment– BonesBones– CartilagesCartilages– Connective tissue coveringsConnective tissue coverings

Smooth Muscle Smooth Muscle CharacteristicsCharacteristics

Has no striationsHas no striations Spindle-shaped Spindle-shaped

cellscells Single nucleusSingle nucleus Involuntary – no Involuntary – no

conscious controlconscious control Found mainly in Found mainly in

the walls of hollow the walls of hollow organsorgans

Cardiac Muscle CharacteristicsCardiac Muscle Characteristics Has striationsHas striations Usually has a Usually has a

single nucleussingle nucleus Joined to another Joined to another

muscle cell at an muscle cell at an intercalated discintercalated disc

InvoluntaryInvoluntary Found only in the Found only in the

heartheart

Function of MusclesFunction of Muscles Produce Produce

movementmovement Maintain postureMaintain posture Stabilize jointsStabilize joints Generate heatGenerate heat

Microscopic Anatomy of Microscopic Anatomy of Skeletal MuscleSkeletal Muscle

Cells are multinucleateCells are multinucleate Nuclei are just beneath the Nuclei are just beneath the

sarcolemmasarcolemma

Microscopic Anatomy of Skeletal Microscopic Anatomy of Skeletal MuscleMuscle

Sarcolemma – specialized plasma Sarcolemma – specialized plasma membranemembrane

Sarcoplasmic reticulum – specialized Sarcoplasmic reticulum – specialized smooth endoplasmic reticulumsmooth endoplasmic reticulum


MyofibrilMyofibril– Bundles of myofilamentsBundles of myofilaments– Myofibrils are aligned to give distinct Myofibrils are aligned to give distinct

bandsbands I band =I band =

light bandlight band A band = A band =

dark banddark band


SarcomereSarcomere– Contractile unit of a muscle fiberContractile unit of a muscle fiber


Organization of the sarcomereOrganization of the sarcomere– Thick filaments = myosin filamentsThick filaments = myosin filaments

Composed of the protein myosinComposed of the protein myosin Has ATPase enzymesHas ATPase enzymes


Organization of the sarcomereOrganization of the sarcomere– Thin filaments = actin filamentsThin filaments = actin filaments

Composed of the protein actinComposed of the protein actin


Myosin filaments have heads Myosin filaments have heads (extensions, or cross bridges)(extensions, or cross bridges)

Myosin and Myosin and actin overlap actin overlap somewhatsomewhat


At rest, there is a bare zone that At rest, there is a bare zone that lacks actin filamentslacks actin filaments

Sarcoplasmic Sarcoplasmic reticulum reticulum (SR) – for (SR) – for storage of storage of calciumcalcium

Properties of Skeletal Muscle Properties of Skeletal Muscle ActivityActivity

Irritability – ability to Irritability – ability to receive and respond to a receive and respond to a stimulusstimulus

Contractility – ability to Contractility – ability to shorten when an shorten when an adequate stimulus is adequate stimulus is receivedreceived

Nerve Stimulus to MusclesNerve Stimulus to Muscles Skeletal muscles Skeletal muscles

must be must be stimulated by a stimulated by a nerve to contractnerve to contract

Motor unitMotor unit– One neuronOne neuron– Muscle cells Muscle cells

stimulated by that stimulated by that neuronneuron

Nerve Stimulus to MusclesNerve Stimulus to Muscles Neuromuscular junctions – Neuromuscular junctions –

association site of nerve and muscleassociation site of nerve and muscle

Nerve Stimulus to MusclesNerve Stimulus to Muscles Synaptic cleft – Synaptic cleft –

gap between nerve gap between nerve and muscleand muscle– Nerve and muscle Nerve and muscle

do not make do not make contactcontact

– Area between Area between nerve and muscle nerve and muscle is filled with is filled with interstitial fluidinterstitial fluid

Transmission of Nerve Impulse Transmission of Nerve Impulse to Muscleto Muscle

Neurotransmitter – chemical released Neurotransmitter – chemical released by nerve upon arrival of nerve by nerve upon arrival of nerve impulseimpulse– The neurotransmitter for skeletal muscle The neurotransmitter for skeletal muscle

is acetylcholineis acetylcholine Neurotransmitter attaches to Neurotransmitter attaches to

receptors on the sarcolemmareceptors on the sarcolemma Sarcolemma becomes permeable to Sarcolemma becomes permeable to

sodium (Nasodium (Na++))

Transmission of Nerve Impulse Transmission of Nerve Impulse to Muscleto Muscle

Sodium rushing into the cell Sodium rushing into the cell generates an action potentialgenerates an action potential

Once started, muscle contraction Once started, muscle contraction cannot be stoppedcannot be stopped

The Sliding Filament Theory of The Sliding Filament Theory of Muscle ContractionMuscle Contraction

Activation by nerve Activation by nerve causes myosin causes myosin heads heads (crossbridges) to (crossbridges) to attach to binding attach to binding sites on the thin sites on the thin filamentfilament

Myosin heads then Myosin heads then bind to the next site bind to the next site of the thin filamentof the thin filament

The Sliding Filament Theory of The Sliding Filament Theory of Muscle ContractionMuscle Contraction

This continued This continued action causes a action causes a sliding of the sliding of the myosin along the myosin along the actinactin

The result is that The result is that the muscle is the muscle is shortened shortened (contracted)(contracted)

The Sliding Filament TheoryThe Sliding Filament Theory

Contraction of a Skeletal Contraction of a Skeletal MuscleMuscle

Muscle fiber contraction is “all or none”Muscle fiber contraction is “all or none” Within a skeletal muscle, not all fibers may Within a skeletal muscle, not all fibers may

be stimulated during the same intervalbe stimulated during the same interval Different combinations of muscle fiber Different combinations of muscle fiber

contractions may give differing responsescontractions may give differing responses Graded responses – different degrees of Graded responses – different degrees of

skeletal muscle shorteningskeletal muscle shortening

Types of Graded ResponsesTypes of Graded Responses

TwitchTwitch– Single, brief contractionSingle, brief contraction– Not a normal muscle functionNot a normal muscle function

Types of Graded ResponsesTypes of Graded Responses

Tetanus (summing of contractions)Tetanus (summing of contractions)– One contraction is immediately followed One contraction is immediately followed

by anotherby another– The muscle does The muscle does

not completely not completely return to a return to a resting stateresting state

– The effects The effects are addedare added

Types of Graded ResponsesTypes of Graded Responses Unfused (incomplete) tetanusUnfused (incomplete) tetanus

– Some relaxation occurs between Some relaxation occurs between contractionscontractions

– The results are summedThe results are summed

Types of Graded ResponsesTypes of Graded Responses Fused (complete) tetanusFused (complete) tetanus

– No evidence of relaxation before the No evidence of relaxation before the following contractionsfollowing contractions

– The result is a sustained muscle The result is a sustained muscle contractioncontraction

Muscle Response to Strong Muscle Response to Strong StimuliStimuli

Muscle force depends upon the Muscle force depends upon the number of fibers stimulatednumber of fibers stimulated

More fibers contracting results in More fibers contracting results in greater muscle tensiongreater muscle tension

Muscles can continue to contract Muscles can continue to contract unless they run out of energyunless they run out of energy

Energy for Muscle Energy for Muscle ContractionContraction

Initially, muscles used stored ATP for Initially, muscles used stored ATP for energyenergy– Bonds of ATP are broken to release Bonds of ATP are broken to release

energyenergy– Only 4-6 seconds worth of ATP is stored Only 4-6 seconds worth of ATP is stored

by musclesby muscles After this initial time, other pathways After this initial time, other pathways

must be utilized to produce ATPmust be utilized to produce ATP


Direct phosphorylationDirect phosphorylation– Muscle cells contain Muscle cells contain

creatine phosphate (CP)creatine phosphate (CP) CP is a high-energy moleculeCP is a high-energy molecule

– After ATP is depleted, ADP After ATP is depleted, ADP is leftis left

– CP transfers energy to CP transfers energy to ADP, to regenerate ATPADP, to regenerate ATP

– CP supplies are exhausted CP supplies are exhausted in about 20 secondsin about 20 seconds


Aerobic RespirationAerobic Respiration– Series of metabolic Series of metabolic

pathways that occur in pathways that occur in the mitochondriathe mitochondria

– Glucose is broken down Glucose is broken down to carbon dioxide and to carbon dioxide and water, releasing energywater, releasing energy

– This is a slower reaction This is a slower reaction that requires continuous that requires continuous oxygenoxygen


Anaerobic glycolysisAnaerobic glycolysis– Reaction that breaks Reaction that breaks

down glucose without down glucose without oxygenoxygen

– Glucose is broken down to Glucose is broken down to pyruvic acid to produce pyruvic acid to produce some ATPsome ATP

– Pyruvic acid is converted Pyruvic acid is converted to lactic acidto lactic acid


Anaerobic Anaerobic glycolysis glycolysis (continued)(continued)– This reaction is This reaction is

not as efficient, not as efficient, but is fastbut is fast Huge amounts of Huge amounts of

glucose are glucose are neededneeded

Lactic acid Lactic acid produces muscle produces muscle fatiguefatigue

Muscle Fatigue and Oxygen Muscle Fatigue and Oxygen DebtDebt

When a muscle is fatigued, it is When a muscle is fatigued, it is unable to contractunable to contract

The common reason for muscle The common reason for muscle fatigue is oxygen debtfatigue is oxygen debt– Oxygen must be “repaid” to tissue to Oxygen must be “repaid” to tissue to

remove oxygen debtremove oxygen debt– Oxygen is required to get rid of Oxygen is required to get rid of

accumulated lactic acidaccumulated lactic acid Increasing acidity (from lactic acid) Increasing acidity (from lactic acid)

and lack of ATP causes the muscle to and lack of ATP causes the muscle to contract lesscontract less

Types of Muscle Types of Muscle ContractionsContractions

Isotonic contractionsIsotonic contractions– Myofilaments are able to slide past each Myofilaments are able to slide past each

other during contractionsother during contractions– The muscle shortensThe muscle shortens

Isometric contractionsIsometric contractions– Tension in the muscles increasesTension in the muscles increases– The muscle is unable to shortenThe muscle is unable to shorten

Muscle ToneMuscle Tone Some fibers are contracted even in a Some fibers are contracted even in a

relaxed musclerelaxed muscle Different fibers contract at different Different fibers contract at different

times to provide muscle tonetimes to provide muscle tone The process of stimulating various The process of stimulating various

fibers is under involuntary controlfibers is under involuntary control

Muscles and Body Muscles and Body MovementsMovements

Movement is Movement is attained due to a attained due to a muscle moving an muscle moving an attached boneattached bone

Muscles and Body Muscles and Body MovementsMovements

Muscles are attached Muscles are attached to at least two pointsto at least two points– Origin – attachment to Origin – attachment to

a moveable bonea moveable bone– Insertion – attachment Insertion – attachment

to an immovable boneto an immovable bone

Five Golden Rules of Gross Five Golden Rules of Gross Muscle ActivityMuscle Activity

1.1. all muscles cross at least one jointall muscles cross at least one joint

2.2. bulk of muscles lies proximal to the bulk of muscles lies proximal to the joint crossedjoint crossed

3.3. all muscles have at least 2 all muscles have at least 2 attachments: origin & insertionattachments: origin & insertion

4.4. muscles only pull/never pushmuscles only pull/never push

5.5. during contraction the muscle during contraction the muscle insertion moves toward the origininsertion moves toward the origin

Effects of Exercise on Effects of Exercise on MuscleMuscle

Aerobics result in stronger muscles Aerobics result in stronger muscles due to increase blood supply due to increase blood supply

Muscle fibers increase Muscle fibers increase mitochondria and oxygen storage mitochondria and oxygen storage Muscle becomes more fatigue resistant

Heart enlarges to pumpHeart enlarges to pump

more blood to bodymore blood to body

Does not increase skeletal Does not increase skeletal

muscle sizemuscle size

Results of increased Results of increased muscle use from muscle use from resistance trainingresistance training

Individual muscle Individual muscle cells make more cells make more contractile filaments contractile filaments & connective tissue & connective tissue increasesincreases– Increase in muscle sizeIncrease in muscle size– Increase in muscle Increase in muscle

strengthstrength

Effects of Exercise on Effects of Exercise on MuscleMuscle

Types of Ordinary Body Types of Ordinary Body MovementsMovements

FlexionFlexion ExtensionExtension RotationRotation AbductionAbduction CircumductionCircumduction

Body MovementsBody Movements

Special MovementsSpecial Movements

DorsifelxionDorsifelxion Plantar flexionPlantar flexion InversionInversion EversionEversion SupinationSupination PronationPronation OppositionOpposition

Types of MusclesTypes of Muscles

Prime mover – muscle with the major Prime mover – muscle with the major responsibility for a certain movementresponsibility for a certain movement

Antagonist – muscle that opposes or Antagonist – muscle that opposes or reverses a prime moverreverses a prime mover

Synergist – muscle that aids a prime Synergist – muscle that aids a prime mover in a movement and helps prevent mover in a movement and helps prevent rotationrotation

Fixator – stabilizes the origin of a prime Fixator – stabilizes the origin of a prime movermover

Naming of Skeletal MusclesNaming of Skeletal Muscles

Direction of muscle fibersDirection of muscle fibers– Example: Example: rectusrectus (straight) (straight)

Relative size of the muscleRelative size of the muscle– Example: Example: maximusmaximus (largest) (largest)


Location of the muscleLocation of the muscle– Example: many muscles are named for Example: many muscles are named for

bones (e.g., bones (e.g., temporalistemporalis)) Number of originsNumber of origins

– Example: Example: tricepstriceps (three heads) (three heads)


Location of the muscle’s origin and Location of the muscle’s origin and insertioninsertion– Example: Example: sternosterno (on the sternum) (on the sternum)

Shape of the muscleShape of the muscle– Example: Example: deltoiddeltoid (triangular) (triangular)

Action of the muscleAction of the muscle– Example: Example: flexorflexor and and extensorextensor (flexes or (flexes or

extends a bone)extends a bone)

Head and Neck MusclesHead and Neck Muscles

Trunk MusclesTrunk Muscles

Deep Trunk and Arm MusclesDeep Trunk and Arm Muscles

Muscles Muscles of the of the Pelvis, Pelvis,

Hip, and Hip, and ThighThigh

Muscles Muscles of the of the Lower Lower LegLeg

SuperficiSuperficial al

Muscles: Muscles: AnteriorAnterior

SuperficiSuperficial al

Muscles: Muscles: PosteriorPosterior

Muscular DystrophyMuscular Dystrophy Congenital muscle-destroying disease Congenital muscle-destroying disease

affect specific muscle groupsaffect specific muscle groups Muscle fibers degenerate & atrophy Muscle fibers degenerate & atrophy

due to an absence of dystrophin, a due to an absence of dystrophin, a protein that helps keep muscle cells protein that helps keep muscle cells intactintact

Most common & serious—Duchenne’s Most common & serious—Duchenne’s M.D.M.D.– Mostly in males Mostly in males (diagnosed between2-6 yrs)(diagnosed between2-6 yrs)– Survival is rare beyond early 30’sSurvival is rare beyond early 30’s– X-linked recessiveX-linked recessive

Myasthenia gravisMyasthenia gravis Rare adult disease caused by Rare adult disease caused by

antibodies to acetylcholine antibodies to acetylcholine receptors at the neuromuscular receptors at the neuromuscular junction which prevents the junction which prevents the muscle contraction from muscle contraction from occurring occurring

Drooping upper eyelids, Drooping upper eyelids, difficulty swallowing & talking, difficulty swallowing & talking, muscle weakness & fatiguemuscle weakness & fatigue

Death occurs when respiratory Death occurs when respiratory muscles cease to functionmuscles cease to function

AgingAging Connective Tissue Connective Tissue

increasesincreases Amount of Muscle tissue Amount of Muscle tissue

decreasesdecreases Muscles become Muscles become

stringier(sinewy)stringier(sinewy) Body weight declines due Body weight declines due

to loss of muscle massto loss of muscle mass By age 80, muscle strength By age 80, muscle strength

usually decrease by 50% usually decrease by 50% without weight training without weight training exercisesexercises

the muscular system alireza ashraf, m.d. professor of physical medicine & rehabilitation shiraz...

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