11

Three Types of Muscle TissueThree Types of Muscle Tissue

1. Smooth muscle tissue2. Skeletal muscle tissue3. Cardiac muscle tissue

22

3 Types of Muscle Tissue3 Types of Muscle Tissue

Skeletal muscleSkeletal muscleattaches to bone, skin or fasciaattaches to bone, skin or fasciastriated with light & dark bands visible striated with light & dark bands visible

with scope with scope voluntary control of contraction & voluntary control of contraction &

relaxationrelaxation

33

3 Types of Muscle Tissue3 Types of Muscle Tissue

Cardiac muscleCardiac musclestriated in appearancestriated in appearanceinvoluntary controlinvoluntary controlautorhythmic because of built in autorhythmic because of built in

pacemakerpacemaker

44

3 Types of Muscle Tissue3 Types of Muscle Tissue

Smooth muscleSmooth muscleattached to hair follicles in skinattached to hair follicles in skinin walls of hollow organs -- blood vessels in walls of hollow organs -- blood vessels

& GI& GInonstriated in appearancenonstriated in appearanceinvoluntaryinvoluntary

55

Functions of Muscle TissueFunctions of Muscle Tissue

Producing body movementsProducing body movementsStabilizing body positionsStabilizing body positionsRegulating organ volumesRegulating organ volumes

bands of smooth muscle called sphinctersbands of smooth muscle called sphinctersMovement of substances within the bodyMovement of substances within the body

blood, lymph, urine, air, food and fluids, spermblood, lymph, urine, air, food and fluids, spermProducing heatProducing heat

involuntary contractions of skeletal muscle involuntary contractions of skeletal muscle (shivering)(shivering)

66

Properties of Muscle TissueProperties of Muscle TissueExcitabilityExcitability

respond to chemicals released from nerve cellsrespond to chemicals released from nerve cellsConductivityConductivity

ability to propagate electrical signals over ability to propagate electrical signals over membranemembrane

ContractilityContractilityability to shorten and generate force ability to shorten and generate force

ExtensibilityExtensibilityability to be stretched without damaging the tissueability to be stretched without damaging the tissue

ElasticityElasticityability to return to original shape after being ability to return to original shape after being

stretchedstretched

77

Skeletal Muscle -- Skeletal Muscle -- Connective Connective TissueTissue

Superficial fascia is Superficial fascia is loose connective tissue & loose connective tissue & fat underlying the skinfat underlying the skin

Deep fascia = dense irregular connective tissue Deep fascia = dense irregular connective tissue around musclearound muscle

Connective tissue components of the muscle Connective tissue components of the muscle includeincludeepimysium = surrounds the whole muscle epimysium = surrounds the whole muscle perimysium = surrounds bundles (fascicles) of perimysium = surrounds bundles (fascicles) of

10-100 muscle cells10-100 muscle cellsendomysium = separates individual muscle cellsendomysium = separates individual muscle cells

All these connective tissue layers extend All these connective tissue layers extend beyond the muscle belly to form the tendon beyond the muscle belly to form the tendon

88

Connective Tissue Connective Tissue ComponentsComponents

99

Nerve and Blood Supply Nerve and Blood Supply Each skeletal muscle is supplied by a Each skeletal muscle is supplied by a

nerve, artery and two veins.nerve, artery and two veins.Each motor neuron supplies multiple Each motor neuron supplies multiple

muscle cells (neuromuscular junction)muscle cells (neuromuscular junction)Each muscle cell is supplied by one Each muscle cell is supplied by one

motor neuron terminal branch and is in motor neuron terminal branch and is in contact with one or two capillaries.contact with one or two capillaries.nerve fibers & capillaries are found in the nerve fibers & capillaries are found in the

endomysium between individual cellsendomysium between individual cells

1010

Fusion of Myoblasts into Muscle Fusion of Myoblasts into Muscle FibersFibers

Every mature muscle cell developed from 100 Every mature muscle cell developed from 100 myoblasts that fuse together in the fetus. myoblasts that fuse together in the fetus. (multinucleated)(multinucleated)

Mature muscle cells can not divideMature muscle cells can not divide Muscle growth is a result of cellular enlargement & Muscle growth is a result of cellular enlargement &

not cell divisionnot cell division Satellite cells retain the ability to regenerate new Satellite cells retain the ability to regenerate new

cells.cells.

1111

Muscle Fiber or MyofibersMuscle Fiber or Myofibers

Muscle cells are long, cylindrical & multinucleated Muscle cells are long, cylindrical & multinucleated Sarcolemma = muscle cell membraneSarcolemma = muscle cell membrane Sarcoplasm filled with tiny threads called myofibrils & Sarcoplasm filled with tiny threads called myofibrils &

myoglobin (red-colored, oxygen-binding protein) myoglobin (red-colored, oxygen-binding protein)

1212

Transverse TubulesTransverse Tubules

T (transverse) tubules are invaginations of the T (transverse) tubules are invaginations of the sarcolemma into the center of the cellsarcolemma into the center of the cell filled with extracellular fluidfilled with extracellular fluid carry muscle action potentials down into cellcarry muscle action potentials down into cell

Mitochondria lie in rows throughout the cellMitochondria lie in rows throughout the cell near the muscle proteins that use ATP during near the muscle proteins that use ATP during

contractioncontraction

1313

Myofibrils & MyofilamentsMyofibrils & Myofilaments

Muscle fibers are filled with threads called Muscle fibers are filled with threads called myofibrils separated by SR (sarcoplasmic myofibrils separated by SR (sarcoplasmic reticulum)reticulum)

Myofilaments (thick & thin filaments) are the Myofilaments (thick & thin filaments) are the contractile proteins of musclecontractile proteins of muscle

1414

Sarcoplasmic Reticulum Sarcoplasmic Reticulum (SR)(SR)

System of tubular sacs similar to smooth System of tubular sacs similar to smooth ER in nonmuscle cellsER in nonmuscle cells

Stores Ca+2 in a relaxed muscleStores Ca+2 in a relaxed muscle Release of Ca+2 triggers muscle Release of Ca+2 triggers muscle

contractioncontraction

1515

Atrophy and HypertrophyAtrophy and Hypertrophy

AtrophyAtrophywasting away of muscleswasting away of musclescaused by disuse (disuse atrophy) or severing caused by disuse (disuse atrophy) or severing

of the nerve supply (denervation atrophy)of the nerve supply (denervation atrophy)the transition to connective tissue can not be the transition to connective tissue can not be

reversedreversedHypertrophyHypertrophy

increase in the diameter of muscle fibers increase in the diameter of muscle fibers resulting from very forceful, repetitive muscular resulting from very forceful, repetitive muscular

activity and an increase in myofibrils, SR & activity and an increase in myofibrils, SR & mitochondriamitochondria

1616

Filaments and the Filaments and the SarcomereSarcomereThick and thin filaments overlap each Thick and thin filaments overlap each

other in a pattern that creates other in a pattern that creates striations (light I bands and dark A striations (light I bands and dark A bands)bands)

The I band region contains only thin The I band region contains only thin filaments.filaments.

They are arranged in compartments They are arranged in compartments called sarcomeres, separated by Z called sarcomeres, separated by Z discs.discs.

In the overlap region, six thin In the overlap region, six thin filaments surround each thick filamentfilaments surround each thick filament

1717

Thick & Thin MyofilamentsThick & Thin Myofilaments

Supporting proteins (M line, titin and Z disc Supporting proteins (M line, titin and Z disc help anchor the thick and thin filaments in help anchor the thick and thin filaments in place)place)

1818

Overlap of Thick & Thin Overlap of Thick & Thin Myofilaments within a MyofibrilMyofilaments within a Myofibril

Dark(A) & light(I) bands visible with an electron microscope

1919

Exercise-Induced Muscle Exercise-Induced Muscle DamageDamage

Intense exercise can cause muscle damageIntense exercise can cause muscle damageelectron micrographs reveal torn sarcolemmas, electron micrographs reveal torn sarcolemmas,

damaged myofibrils an disrupted Z discsdamaged myofibrils an disrupted Z discsincreased blood levels of myoglobin & creatine increased blood levels of myoglobin & creatine

phosphate found only inside muscle cellsphosphate found only inside muscle cellsDelayed onset muscle sorenessDelayed onset muscle soreness

12 to 48 Hours after strenuous exercise12 to 48 Hours after strenuous exercisestiffness, tenderness and swelling due to stiffness, tenderness and swelling due to

microscopic cell damagemicroscopic cell damage

2020

The Proteins of MuscleThe Proteins of Muscle

Myofibrils are built of 3 kinds of proteinMyofibrils are built of 3 kinds of proteincontractile proteinscontractile proteins

myosin and actinmyosin and actinregulatory proteins which turn contraction regulatory proteins which turn contraction

on & offon & offtroponin and tropomyosintroponin and tropomyosin

structural proteins which provide proper structural proteins which provide proper alignment, elasticity and extensibilityalignment, elasticity and extensibilitytitin, myomesin, nebulin and dystrophintitin, myomesin, nebulin and dystrophin

2121

The Proteins of Muscle -- MyosinThe Proteins of Muscle -- Myosin

Thick filaments are composed of myosin Thick filaments are composed of myosin each molecule resembles two golf clubs twisted togethereach molecule resembles two golf clubs twisted together myosin heads (cross bridges) extend toward the thin myosin heads (cross bridges) extend toward the thin

filamentsfilaments Held in place by the M line proteins.Held in place by the M line proteins.

2222

The Proteins of Muscle -- ActinThe Proteins of Muscle -- Actin

Thin filaments are made of actin, troponin, & tropomyosin Thin filaments are made of actin, troponin, & tropomyosin The myosin-binding site on each actin molecule is The myosin-binding site on each actin molecule is

covered by tropomyosin in relaxed musclecovered by tropomyosin in relaxed muscle The thin filaments are held in place by Z lines. From one The thin filaments are held in place by Z lines. From one

Z line to the next is a sarcomere.Z line to the next is a sarcomere.

2323

Sliding Filament Mechanism Of Sliding Filament Mechanism Of

ContractionContraction Myosin cross bridgesMyosin cross bridgespull on thin filamentspull on thin filaments

Thin filaments slide Thin filaments slide inwardinward

Z Discs come toward Z Discs come toward each othereach other

Sarcomeres Sarcomeres shorten.The muscle shorten.The muscle fiber shortens. The fiber shortens. The muscle shortensmuscle shortens

Notice :Thick & thin Notice :Thick & thin filaments do not filaments do not change in lengthchange in length

2424

How Does Contraction How Does Contraction Begin?Begin?

Nerve impulse reaches an axon terminal & Nerve impulse reaches an axon terminal & synaptic vesicles release acetylcholine (ACh)synaptic vesicles release acetylcholine (ACh)

ACh diffuses to receptors on the sarcolemma ACh diffuses to receptors on the sarcolemma & Na+ channels open and Na+ rushes into & Na+ channels open and Na+ rushes into the cellthe cell

A muscle action potential spreads over A muscle action potential spreads over sarcolemma and down into the transverse sarcolemma and down into the transverse tubulestubules

SR releases Ca+2 into the sarcoplasmSR releases Ca+2 into the sarcoplasmCa+2 binds to troponin & causes troponin-Ca+2 binds to troponin & causes troponin-

tropomyosin complex to move & reveal tropomyosin complex to move & reveal myosin binding sites on actin--the myosin binding sites on actin--the contraction cycle beginscontraction cycle begins

2525

Excitation - Contraction CouplingExcitation - Contraction Coupling

All the steps that occur from the muscle action All the steps that occur from the muscle action potential reaching the T tubule to contraction of potential reaching the T tubule to contraction of the muscle fiber.the muscle fiber.

2626

Contraction CycleContraction CycleRepeating sequence of events that cause the Repeating sequence of events that cause the

thick & thin filaments to move past each thick & thin filaments to move past each other.other.

4 steps to contraction cycle4 steps to contraction cycleATP hydrolysisATP hydrolysisattachment of myosin to actin to form attachment of myosin to actin to form

crossbridgescrossbridgespower strokepower strokedetachment of myosin from actindetachment of myosin from actin

Cycle keeps repeating as long as there is ATP Cycle keeps repeating as long as there is ATP available & high Ca+2 level near thin available & high Ca+2 level near thin filamentfilament

2727

Steps in the Contraction CycleSteps in the Contraction Cycle

Notice how the myosin head attaches and pulls on Notice how the myosin head attaches and pulls on the thin filament with the energy released from ATPthe thin filament with the energy released from ATP

2828

ATP and MyosinATP and Myosin

Myosin heads are activated by ATPMyosin heads are activated by ATP Activated heads attach to actin & pull (power Activated heads attach to actin & pull (power

stroke)stroke) ADP is released. (ATP released P & ADP & energy)ADP is released. (ATP released P & ADP & energy) Thin filaments slide past the thick filamentsThin filaments slide past the thick filaments ATP binds to myosin head & detaches it from actinATP binds to myosin head & detaches it from actin All of these steps repeat over and overAll of these steps repeat over and over

if ATP is available &if ATP is available & Ca+ level near the troponin-tropomyosin complex is highCa+ level near the troponin-tropomyosin complex is high

2929

Overview: From Start to Overview: From Start to FinishFinish

Nerve endingNerve ending NeurotransmittNeurotransmitt

oror Muscle Muscle

membranemembrane Stored Ca+2Stored Ca+2 ATPATP Muscle proteinsMuscle proteins

3030

RelaxationRelaxationAcetylcholinesterase (AChE) breaks down Acetylcholinesterase (AChE) breaks down

ACh within the synaptic cleftACh within the synaptic cleftMuscle action potential ceasesMuscle action potential ceasesCa+2 release channels closeCa+2 release channels closeActive transport pumps Ca2+ back into Active transport pumps Ca2+ back into

storage in the sarcoplasmic reticulumstorage in the sarcoplasmic reticulumCalcium-binding protein (calsequestrin) Calcium-binding protein (calsequestrin)

helps hold Ca+2 in SR (Ca+2 helps hold Ca+2 in SR (Ca+2 concentration 10,000 times higher than in concentration 10,000 times higher than in cytosol)cytosol)

Tropomyosin-troponin complex recovers Tropomyosin-troponin complex recovers binding site on the actinbinding site on the actin

3131

Rigor MortisRigor MortisRigor mortis is a state of muscular Rigor mortis is a state of muscular

rigidity that begins 3-4 hours after death rigidity that begins 3-4 hours after death and lasts about 24 hoursand lasts about 24 hours

After death, Ca+2 ions leak out of the SR After death, Ca+2 ions leak out of the SR and allow myosin heads to bind to actinand allow myosin heads to bind to actin

Since ATP synthesis has ceased, Since ATP synthesis has ceased, crossbridges cannot detach from actin crossbridges cannot detach from actin until proteolytic enzymes begin to digest until proteolytic enzymes begin to digest the decomposing cells.the decomposing cells.

3232

Structures of NMJ RegionStructures of NMJ Region

Synaptic end bulbs are Synaptic end bulbs are swellings of axon terminalsswellings of axon terminals

End bulbs contain synaptic End bulbs contain synaptic vesicles filled with vesicles filled with acetylcholine (ACh)acetylcholine (ACh)

Motor end plate Motor end plate membrane contains 30 membrane contains 30 million ACh receptors.million ACh receptors.

3333

Events Occurring After a Nerve Events Occurring After a Nerve SignalSignal

Arrival of nerve impulse at nerve terminal causes Arrival of nerve impulse at nerve terminal causes release of ACh from synaptic vesiclesrelease of ACh from synaptic vesicles

ACh binds to receptors on muscle motor end plate ACh binds to receptors on muscle motor end plate opening the gated ion channels so that Na+ can opening the gated ion channels so that Na+ can rush into the muscle cellrush into the muscle cell

Inside of muscle cell becomes more positive, Inside of muscle cell becomes more positive, triggering a muscle action potential that travels triggering a muscle action potential that travels over the cell and down the T tubulesover the cell and down the T tubules

The release of Ca+2 from the SR is triggered and The release of Ca+2 from the SR is triggered and the muscle cell will shorten & generate forcethe muscle cell will shorten & generate force

Acetylcholinesterase breaks down the ACh Acetylcholinesterase breaks down the ACh attached to the receptors on the motor end plate attached to the receptors on the motor end plate so the muscle action potential will cease and the so the muscle action potential will cease and the muscle cell will relax.muscle cell will relax.

3434

Pharmacology of the NMJPharmacology of the NMJBotulinum toxin blocks release of neurotransmitter at the Botulinum toxin blocks release of neurotransmitter at the

NMJ so muscle contraction can not occurNMJ so muscle contraction can not occurbacteria found in improperly canned foodbacteria found in improperly canned fooddeath occurs from paralysis of the diaphragmdeath occurs from paralysis of the diaphragm

Curare (plant poison from poison arrows)Curare (plant poison from poison arrows)causes muscle paralysis by blocking the ACh receptors causes muscle paralysis by blocking the ACh receptors used to relax muscle during surgeryused to relax muscle during surgery

Neostigmine (anticholinesterase agent)Neostigmine (anticholinesterase agent)blocks removal of ACh from receptors so strengthens weak blocks removal of ACh from receptors so strengthens weak

muscle contractions of myasthenia gravismuscle contractions of myasthenia gravisalso an antidote for curare after surgery is finishedalso an antidote for curare after surgery is finished

3535

Muscle MetabolismMuscle MetabolismProduction of ATP in Muscle FibersProduction of ATP in Muscle Fibers

Muscle uses ATP at a great rate when Muscle uses ATP at a great rate when activeactive

Sarcoplasmic ATP only lasts for few Sarcoplasmic ATP only lasts for few secondsseconds

3 sources of ATP production within 3 sources of ATP production within musclemusclecreatine phosphatecreatine phosphateanaerobic cellular respirationanaerobic cellular respirationanaerobic cellular respirationanaerobic cellular respiration

3636

Anaerobic Cellular Anaerobic Cellular RespirationRespiration

ATP produced from ATP produced from glucose breakdown into glucose breakdown into pyruvic acid during pyruvic acid during glycolysis glycolysis if no O2 presentif no O2 present

pyruvic converted to pyruvic converted to lactic acid which diffuses lactic acid which diffuses into the bloodinto the blood

Glycolysis can continue Glycolysis can continue anaerobically to provide anaerobically to provide ATP for 30 to 40 seconds ATP for 30 to 40 seconds of maximal activity (200 of maximal activity (200 meter race)meter race)

3737

Aerobic Cellular RespirationAerobic Cellular Respiration

ATP for any activity lasting over 30 seconds ATP for any activity lasting over 30 seconds if sufficient oxygen is available, pyruvic acid enters if sufficient oxygen is available, pyruvic acid enters

the mitochondria to generate ATP, water and heatthe mitochondria to generate ATP, water and heat fatty acids and amino acids can also be used by the fatty acids and amino acids can also be used by the

mitochondriamitochondria Provides 90% of ATP energy if activity lasts Provides 90% of ATP energy if activity lasts

more than 10 minutesmore than 10 minutes

3838

Muscle FatigueMuscle Fatigue Inability to contract after prolonged Inability to contract after prolonged

activityactivitycentral fatigue is feeling of tiredness and a central fatigue is feeling of tiredness and a

desire to stop (protective mechanism)desire to stop (protective mechanism)depletion of creatine phosphatedepletion of creatine phosphatedecline of Ca+2 within the sarcoplasmdecline of Ca+2 within the sarcoplasm

Factors that contribute to muscle Factors that contribute to muscle fatiguefatigueinsufficient oxygen or glycogeninsufficient oxygen or glycogenbuildup of lactic acid and ADPbuildup of lactic acid and ADPinsufficient release of acetylcholine from insufficient release of acetylcholine from

motor neurons motor neurons

3939

Oxygen Consumption after Oxygen Consumption after ExerciseExercise

Muscle tissue has two sources of oxygen.Muscle tissue has two sources of oxygen.diffuses in from the blooddiffuses in from the bloodreleased by myoglobin inside muscle fibersreleased by myoglobin inside muscle fibers

Aerobic system requires O2 to produce ATP Aerobic system requires O2 to produce ATP needed for prolonged activityneeded for prolonged activityincreased breathing effort during exercise increased breathing effort during exercise

Recovery oxygen uptakeRecovery oxygen uptakeelevated oxygen use after exercise (oxygen elevated oxygen use after exercise (oxygen

debt)debt)lactic acid is converted back to pyruvic acidlactic acid is converted back to pyruvic acidelevated body temperature means all reactions elevated body temperature means all reactions

fasterfaster

4040

Muscle ToneMuscle Tone Involuntary contraction of a small number Involuntary contraction of a small number

of motor units (alternately active and of motor units (alternately active and inactive in a constantly shifting pattern)inactive in a constantly shifting pattern)keeps muscles firm even though relaxedkeeps muscles firm even though relaxeddoes not produce movement does not produce movement

Essential for maintaining posture (head Essential for maintaining posture (head upright)upright)

Important in maintaining blood pressureImportant in maintaining blood pressuretone of smooth muscles in walls of blood tone of smooth muscles in walls of blood

vesselsvessels

4141

Classification of Muscle FibersClassification of Muscle Fibers

Slow oxidative (slow-twitch)Slow oxidative (slow-twitch) red in color (lots of mitochondria, myoglobin & blood vessels)red in color (lots of mitochondria, myoglobin & blood vessels) prolonged, sustained contractions for maintaining postureprolonged, sustained contractions for maintaining posture

Fast oxidative-glycolytic (fast-twitch A)Fast oxidative-glycolytic (fast-twitch A) red in color (lots of mitochondria, myoglobin & blood vessels)red in color (lots of mitochondria, myoglobin & blood vessels) split ATP at very fast rate; used for walking and sprintingsplit ATP at very fast rate; used for walking and sprinting

Fast glycolytic (fast-twitch B)Fast glycolytic (fast-twitch B) white in color (few mitochondria & BV, low myoglobin)white in color (few mitochondria & BV, low myoglobin) anaerobic movements for short duration; used for weight-anaerobic movements for short duration; used for weight-

liftinglifting

4242

Fiber Types within a Whole Fiber Types within a Whole MuscleMuscle

Most muscles contain a mixture of all Most muscles contain a mixture of all three fiber typesthree fiber types

Proportions vary with the usual action of Proportions vary with the usual action of the musclethe muscleneck, back and leg muscles have a higher neck, back and leg muscles have a higher

proportion of postural, slow oxidative fibersproportion of postural, slow oxidative fibersshoulder and arm muscles have a higher shoulder and arm muscles have a higher

proportion of fast glycolytic fibersproportion of fast glycolytic fibersAll fibers of any one motor unit are same.All fibers of any one motor unit are same.Different fibers are recruited as needed.Different fibers are recruited as needed.

4343

Anabolic SteroidsAnabolic Steroids

Similar to testosteroneSimilar to testosterone Increases muscle size, strength, and Increases muscle size, strength, and

enduranceenduranceMany very serious side effectsMany very serious side effects

liver cancerliver cancerkidney damagekidney damageheart diseaseheart diseasemood swingsmood swingsfacial hair & voice deepening in femalesfacial hair & voice deepening in femalesatrophy of testicles & baldness in malesatrophy of testicles & baldness in males

4444

Anatomy of Cardiac MuscleAnatomy of Cardiac Muscle

Striated , short, quadrangular-shaped, branching fibers Striated , short, quadrangular-shaped, branching fibers Single centrally located nucleusSingle centrally located nucleus Cells connected by intercalated discs with gap Cells connected by intercalated discs with gap

junctionsjunctions Same arrangement of thick & thin filaments as skeletalSame arrangement of thick & thin filaments as skeletal

4545

Cardiac versus Skeletal Cardiac versus Skeletal MuscleMuscle

More sarcoplasm and mitochondriaMore sarcoplasm and mitochondriaLarger transverse tubules located at Z Larger transverse tubules located at Z

discs, rather than at A-l band junctionsdiscs, rather than at A-l band junctionsLess well-developed SRLess well-developed SRLimited intracellular Ca+2 reservesLimited intracellular Ca+2 reserves

more Ca+2 enters cell from extracellular more Ca+2 enters cell from extracellular fluid during contractionfluid during contraction

Prolonged delivery of Ca+2 to Prolonged delivery of Ca+2 to sarcoplasm, produces a contraction sarcoplasm, produces a contraction that last 10 -15 times longer than in that last 10 -15 times longer than in skeletal muscleskeletal muscle

4646

Physiology of Cardiac Physiology of Cardiac MuscleMuscle

Autorhythmic cellsAutorhythmic cellscontract without stimulationcontract without stimulation

Contracts 75 times per min & needs lots O2 Contracts 75 times per min & needs lots O2 Larger mitochondria generate ATP aerobically Larger mitochondria generate ATP aerobically Sustained contraction possible due to slow Sustained contraction possible due to slow

Ca+2 deliveryCa+2 deliveryCa+2 channels to the extracellular fluid stay openCa+2 channels to the extracellular fluid stay open

4747

Two Types of Smooth Two Types of Smooth MuscleMuscle

Visceral (single-unit)Visceral (single-unit) in the walls of hollow in the walls of hollow

viscera & small BVviscera & small BV autorhythmicautorhythmic gap junctions cause gap junctions cause

fibers to contract in fibers to contract in unisonunison

Multiunit Multiunit individual fibers with individual fibers with

own motor neuron own motor neuron endingending

found in large arteries, found in large arteries, large airways, arrector large airways, arrector pili muscles,iris & pili muscles,iris & ciliary bodyciliary body

4848

Physiology of Smooth Physiology of Smooth MuscleMuscle

Contraction starts slowly & lasts longerContraction starts slowly & lasts longerno transverse tubules & very little SRno transverse tubules & very little SRCa+2 must flows in from outsideCa+2 must flows in from outside

Calmodulin replaces troponinCalmodulin replaces troponinCa+2 binds to calmodulin turning on an Ca+2 binds to calmodulin turning on an

enzyme (myosin light chain kinase) that enzyme (myosin light chain kinase) that phosphorylates the myosin head so that phosphorylates the myosin head so that contraction can occurcontraction can occur

enzyme works slowly, slowing contractionenzyme works slowly, slowing contraction

4949

Smooth Muscle ToneSmooth Muscle Tone

Ca+2 moves slowly out of the cellCa+2 moves slowly out of the celldelaying relaxation and providing for delaying relaxation and providing for

state of continued partial contraction state of continued partial contraction sustained long-termsustained long-term

Useful for maintaining blood Useful for maintaining blood pressure or a steady pressure on the pressure or a steady pressure on the contents of GI tract contents of GI tract

5050

Regeneration of MuscleRegeneration of MuscleSkeletal muscle fibers cannot divide after 1st yearSkeletal muscle fibers cannot divide after 1st year

growth is enlargement of existing cellsgrowth is enlargement of existing cellsrepairrepair

satellite cells & bone marrow produce some new cellssatellite cells & bone marrow produce some new cellsif not enough numbers---fibrosis occurs most oftenif not enough numbers---fibrosis occurs most often

Cardiac muscle fibers cannot divide or regenerateCardiac muscle fibers cannot divide or regenerateall healing is done by fibrosis (scar formation)all healing is done by fibrosis (scar formation)

Smooth muscle fibers (regeneration is possible)Smooth muscle fibers (regeneration is possible)cells can grow in size (hypertrophy)cells can grow in size (hypertrophy)some cells (uterus) can divide (hyperplasia)some cells (uterus) can divide (hyperplasia)new fibers can form from stem cells in BV wallsnew fibers can form from stem cells in BV walls

5151

Aging and Muscle TissueAging and Muscle Tissue

Skeletal muscle starts to be replaced by fat Skeletal muscle starts to be replaced by fat beginning at 30 beginning at 30 ““use it or lose it”use it or lose it”

Slowing of reflexes & decrease in maximal strengthSlowing of reflexes & decrease in maximal strengthChange in fiber type to slow oxidative fibers may Change in fiber type to slow oxidative fibers may

be due to lack of use or may be result of agingbe due to lack of use or may be result of aging

5252

Myasthenia GravisMyasthenia GravisProgressive autoimmune disorder that blocks Progressive autoimmune disorder that blocks

the ACh receptors at the neuromuscular junction the ACh receptors at the neuromuscular junction The more receptors are damaged the weaker The more receptors are damaged the weaker

the muscle. the muscle. More common in women 20 to 40 with possible More common in women 20 to 40 with possible

line to thymus gland tumorsline to thymus gland tumorsBegins with double vision & swallowing Begins with double vision & swallowing

difficulties & progresses to paralysis of difficulties & progresses to paralysis of respiratory muscles respiratory muscles

Treatment includes steroids that reduce Treatment includes steroids that reduce antibodies that bind to ACh receptors and antibodies that bind to ACh receptors and inhibitors of acetylcholinesterase inhibitors of acetylcholinesterase

5353

Muscular Dystrophies Muscular Dystrophies Inherited, muscle-destroying diseases Inherited, muscle-destroying diseases Sarcolemma tears during muscle contractionSarcolemma tears during muscle contractionMutated gene is on X chromosome so problem is Mutated gene is on X chromosome so problem is

with males almost exclusivelywith males almost exclusivelyAppears by age 5 in males and by 12 may be Appears by age 5 in males and by 12 may be

unable to walkunable to walkDegeneration of individual muscle fibers produces Degeneration of individual muscle fibers produces

atrophy of the skeletal muscleatrophy of the skeletal muscleGene therapy is hoped for with the most common Gene therapy is hoped for with the most common

form = Duchenne muscular dystrophyform = Duchenne muscular dystrophy

5454

Abnormal ContractionsAbnormal ContractionsSpasm = involuntary contraction of Spasm = involuntary contraction of

single musclesingle muscleCramp = a painful spasmCramp = a painful spasmTic = involuntary twitching of muscles Tic = involuntary twitching of muscles

normally under voluntary control--normally under voluntary control--eyelid or facial muscleseyelid or facial muscles

Tremor = rhythmic, involuntary Tremor = rhythmic, involuntary contraction of opposing muscle groupscontraction of opposing muscle groups

Fasciculation = involuntary, brief Fasciculation = involuntary, brief twitch of a motor unit visible under twitch of a motor unit visible under the skinthe skin