Figure 68 Contraction of a Skeletal Muscle Muscle fiber contraction is all or none Within a skeletal muscle not all fibers may be stimulated during the same interval Different combinations of muscle fiber contractions may give differing responses ID: 661423
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Slide1
The Muscular SystemSlide2
The Sliding Filament Theory
Figure 6.8Slide3
Contraction of a Skeletal Muscle
Muscle fiber contraction is “all or none”
Within a skeletal muscle, not all fibers may be stimulated during the same intervalDifferent combinations of muscle fiber contractions may give differing responsesGraded responses – different degrees of skeletal muscle shorteningSlide4
Types of Graded Responses
Twitch
Single, brief contractionNot a normal muscle function
Figure 6.9a–bSlide5
Types of Graded Responses
Tetanus (summing of contractions)
One contraction is immediately followed by anotherThe muscle does not completely return to a
resting stateThe effects are added
Figure 6.9a–bSlide6
Types of Graded Responses
Unfused (incomplete) tetanus
Some relaxation occurs between contractionsThe results are summed
Figure 6.9c–dSlide7
Types of Graded Responses
Fused (complete) tetanus
No evidence of relaxation before the following contractionsThe result is a sustained muscle contraction
Figure 6.9c–dSlide8
Muscle Response to Strong Stimuli
Muscle force depends upon the number of fibers stimulated
More fibers contracting results in greater muscle tensionMuscles can continue to contract unless they run out of energySlide9
Energy for Muscle Contraction
Initially, muscles used stored ATP for energy
Bonds of ATP are broken to release energyOnly 4-6 seconds worth of ATP is stored by musclesAfter this initial time, other pathways must be utilized to produce ATPSlide10
Energy for Muscle Contraction
Direct phosphorylation
Muscle cells contain creatine phosphate (CP)
CP is a high-energy moleculeAfter ATP is depleted, ADP is leftCP transfers energy to ADP, to regenerate ATP
CP supplies are exhausted in about 20 seconds
Figure 6.10aSlide11
Energy for Muscle Contraction
Aerobic Respiration
Series of metabolic pathways that occur in the mitochondriaGlucose is broken down to carbon dioxide and water, releasing energy
This is a slower reaction that requires continuous oxygen
Figure 6.10bSlide12
Energy for Muscle Contraction
Anaerobic glycolysis
Reaction that breaks down glucose without oxygenGlucose is broken down to pyruvic acid to produce some ATPPyruvic acid is converted to lactic acid
Figure 6.10cSlide13
Energy for Muscle Contraction
Anaerobic glycolysis (continued)
This reaction is not as efficient, but is fastHuge amounts of glucose are neededLactic acid produces muscle fatigue
Figure 6.10cSlide14
Muscle Fatigue and Oxygen Debt
When a muscle is fatigued, it is unable to contract
The common reason for muscle fatigue is oxygen debtOxygen must be “repaid” to tissue to remove oxygen debt
Oxygen is required to get rid of accumulated lactic acidIncreasing acidity (from lactic acid) and lack of ATP causes the muscle to contract lessSlide15
Types of Muscle Contractions
Isotonic contractions
Myofilaments are able to slide past each other during contractionsThe muscle shortensIsometric contractionsTension in the muscles increases
The muscle is unable to shortenSlide16
Muscle Tone
Some fibers are contracted even in a relaxed muscle
Different fibers contract at different times to provide muscle toneThe process of stimulating various fibers is under involuntary controlSlide17
Muscles and Body Movements
Movement is attained due to a muscle moving an attached bone
Figure 6.12Slide18
Muscles and Body Movements
Muscles are attached to at least two points
Origin – attachment to a moveable boneInsertion – attachment to an immovable bone
Figure 6.12Slide19
Effects of Exercise on Muscle
Results of increased muscle use
Increase in muscle sizeIncrease in muscle strengthIncrease in muscle efficiencyMuscle becomes more fatigue resistant