This document compares smooth muscle contraction to skeletal muscle contraction. Some key points: - Smooth muscle requires 1/300 the energy of skeletal muscle to sustain the same tension. It uses one ATP per contraction cycle. - Smooth muscle contraction is prolonged, lasting 1-3 seconds, while skeletal muscle contracts and relaxes rapidly. - Smooth muscle is able to maintain contraction, or "latch", with very little energy through prolonged cross-bridge attachment and reduced myosin phosphorylation rates. - Calcium regulation of contraction is similar between muscle types but smooth muscle response is much slower.

1. COMPARISON OF SMOOTHCOMPARISON OF SMOOTH
MUSCLE CONTRACTION ANDMUSCLE CONTRACTION AND
SKELETAL MUSCLESKELETAL MUSCLE
CONTRACTIONCONTRACTION
Detailed comparisonDetailed comparison

2. ENERGY REQUIRED TO SUSTAINENERGY REQUIRED TO SUSTAIN
SMOOTH MUSCLE CONTRACTIONSMOOTH MUSCLE CONTRACTION
Frequency is 1/10 to 1/300 energy isFrequency is 1/10 to 1/300 energy is
required to sustain the same tension ofrequired to sustain the same tension of
contraction is smooth muscle as incontraction is smooth muscle as in
skeletal muscleskeletal muscle
Only one ATP is required for whole cycleOnly one ATP is required for whole cycle

3. Skeletal musclesSkeletal muscles
Rapid contraction andRapid contraction and
relaxation in skeletalrelaxation in skeletal
musclesmuscles
Rapidity of cyclingRapidity of cycling
Fraction of time is greaterFraction of time is greater
Greater activity ofGreater activity of
ATPaseATPase
Rapid cycling andRapid cycling and
degradationdegradation
Smooth musclesSmooth muscles
Smooth muscleSmooth muscle
contraction is prolongedcontraction is prolonged
Slowness of cyclingSlowness of cycling
Much much slowerMuch much slower
Far less ATPase activityFar less ATPase activity
Slow cyclingSlow cycling
COMPARISON OF SMOOTH MUSCLECOMPARISON OF SMOOTH MUSCLE
CONTRACTION AND SKELETAL MUSCLECONTRACTION AND SKELETAL MUSCLE
CONTRACTIONCONTRACTION

4. Energy required to sustainEnergy required to sustain
smooth muscle contractionsmooth muscle contraction
Skeletal musclesSkeletal muscles
1/101/10
Smooth musclesSmooth muscles
1/3001/300
One ATP for one cycleOne ATP for one cycle

5. SLOWNESS OF ONSET OFSLOWNESS OF ONSET OF
CONTRACTION AND RELAXATION OFCONTRACTION AND RELAXATION OF
THE SMOOTH MUSCLE TISSUETHE SMOOTH MUSCLE TISSUE
Time for contraction after excitationTime for contraction after excitation
50-100ms50-100ms
Reaches full contraction afterReaches full contraction after
0.5s0.5s
Decline in contractile forceDecline in contractile force
1-2s1-2s
Total contraction timeTotal contraction time
1-3s1-3s

6. SLOWNESS OF ONSET OFSLOWNESS OF ONSET OF
CONTRACTION AND RELAXATION OFCONTRACTION AND RELAXATION OF
THE SMOOTH MUSCLE TISSUETHE SMOOTH MUSCLE TISSUE
3o times long in comparison of skeletal3o times long in comparison of skeletal
muscle fibersmuscle fibers
Reasons for tonic and prolongedReasons for tonic and prolonged
contractioncontraction
Slow attachment and detachment of crossSlow attachment and detachment of cross
bridgesbridges
Response to calcium ions is much slowerResponse to calcium ions is much slower

7. FORCE OF MUSCLEFORCE OF MUSCLE
CONTRACTIONCONTRACTION
Few myosin filamentsFew myosin filaments
Maximum force of contractionMaximum force of contraction
For skeletal musclesFor skeletal muscles
3-4kg/cm2 cross sectional area3-4kg/cm2 cross sectional area
For smooth musclesFor smooth muscles
4-6kg/cm2 cross sectional area4-6kg/cm2 cross sectional area
Prolonged period of attachment inProlonged period of attachment in
contractioncontraction

8. LATCH MECHANISMLATCH MECHANISM
Consumption of less energy forConsumption of less energy for
maintenance of contraction as 1/300maintenance of contraction as 1/300
Prolonged tonic contractionProlonged tonic contraction
Cross bridges phosphorylationCross bridges phosphorylation
ATP consumption rates fallATP consumption rates fall
Little excitatory signalsLittle excitatory signals
Hormonal signalsHormonal signals

9. STRESS-RELAXATION OFSTRESS-RELAXATION OF
SMOOTH MUSCLESSMOOTH MUSCLES
Sudden increase in volume of fluid in urinarySudden increase in volume of fluid in urinary
bladderbladder
Stretching the bladderStretching the bladder
Increase in pressureIncrease in pressure
After some time pressure comes to original levelAfter some time pressure comes to original level

10. STRESS-RELAXATION OFSTRESS-RELAXATION OF
SMOOTH MUSCLESSMOOTH MUSCLES
Decrease in volumeDecrease in volume
Pressure fallsPressure falls
Comes to original levelComes to original level
Maintenance of pressureMaintenance of pressure

11. DEFINATION OF STRESSDEFINATION OF STRESS
RELAXATION MECHANISMRELAXATION MECHANISM
Ability to return to nearly its original forceAbility to return to nearly its original force
of contraction sec or min after it has beenof contraction sec or min after it has been
elongated or shortenedelongated or shortened
Characteristics of unitary type of smoothCharacteristics of unitary type of smooth
muscles ofmuscles of visceral type of hollow organsvisceral type of hollow organs

12. REGULATION OF CONCENTRATIONREGULATION OF CONCENTRATION
BY CALCIUM IONSBY CALCIUM IONS
Initiation of stimulus for skeletal musclesInitiation of stimulus for skeletal muscles
as well as for smooth musclesas well as for smooth muscles
Rise in intracellular level of calcium ionsRise in intracellular level of calcium ions
By means of nerve stimulationBy means of nerve stimulation
Hormonal signalsHormonal signals
Stretching of fibersStretching of fibers
Sphingosine 1 phosphateSphingosine 1 phosphate
Change in chemical environment of fiberChange in chemical environment of fiber

13. REGULATION OF CONCENTRATIONREGULATION OF CONCENTRATION
BY CALCIUM IONSBY CALCIUM IONS
Regulatory proteinRegulatory protein
CalmodulinCalmodulin
Similar to troponinSimilar to troponin
Manner of initation of contraction isManner of initation of contraction is
differentdifferent

14. SEQUENCE IOF EVENTSSEQUENCE IOF EVENTS
Binding of neurotransmitterBinding of neurotransmitter
Influx of calcium ionsInflux of calcium ions
Binding of calcium ions with calmodulinBinding of calcium ions with calmodulin
Calmodulin-calcium combination joins withCalmodulin-calcium combination joins with
myosin kinasemyosin kinase

15. SEQUENCE IOF EVENTSSEQUENCE IOF EVENTS
Myosin kinaseMyosin kinase
A phosphorylating enzymeA phosphorylating enzyme
One light chain of myosin head is calledOne light chain of myosin head is called
regulatory chainregulatory chain
Phosphorylation of myosinPhosphorylation of myosin
Binding of actin to myosin due to myosinBinding of actin to myosin due to myosin
ATPaseATPase
Cross bridges formation occursCross bridges formation occurs

16. SEQUENCE IOF EVENTSSEQUENCE IOF EVENTS
ContractionContraction
Dephosphorylation of myosinDephosphorylation of myosin
RelaxationRelaxation
Sustained contraction (latch mechanism)Sustained contraction (latch mechanism)

18. ROLE OF MYOSINROLE OF MYOSIN
PHOSPHATASEPHOSPHATASE
Calcium levels falls below critical levelCalcium levels falls below critical level
Cessation of contractionCessation of contraction
Located in fluids of smooth musclesLocated in fluids of smooth muscles
Splits phosphate from regulatory chainSplits phosphate from regulatory chain
Cycling stopsCycling stops

19. POSSIBLE MECHANISM FORPOSSIBLE MECHANISM FOR
REGULATION OF THE LATCHREGULATION OF THE LATCH
MECHANISMMECHANISM
Activation of myosin kinase and myosinActivation of myosin kinase and myosin
phosphatasephosphatase
Cycling frequency occursCycling frequency occurs
Velocity of contraction is greatVelocity of contraction is great
Activation of enzyme decreasesActivation of enzyme decreases
Low cycling decreasesLow cycling decreases
Deactivation of both enzymesDeactivation of both enzymes
Permit myosin heads to remain attached to actinPermit myosin heads to remain attached to actin
filamentfilament

20. HOW SMOOTH MUSCLESHOW SMOOTH MUSCLES
MAINTAIN CONTRATION?MAINTAIN CONTRATION?
Can produce fewer ATPCan produce fewer ATP
SR is much less developedSR is much less developed
Fewer Ca ATPase mole on its membraneFewer Ca ATPase mole on its membrane

21. IMPORTANCE OF LATCHIMPORTANCE OF LATCH
MECHANISMMECHANISM
Less consumption of energyLess consumption of energy
Less time requiredLess time required