The Muscular System. Contraction of Skeletal Muscle Muscle fiber contraction is “all or none”...
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Transcript of The Muscular System. Contraction of Skeletal Muscle Muscle fiber contraction is “all or none”...
Contraction of Skeletal MuscleMuscle 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 shortening
Contraction of Skeletal MuscleGraded responses can be produced by
changingThe frequency of muscle stimulationThe number of muscle cells being stimulated
at one time
Types of Graded ResponsesTetanus (summing of contractions)
One contraction is immediately followed by another
The muscle does not completely return to a resting state
The effects are added
Types of Graded ResponsesUnfused (incomplete) tetanus
Some relaxation occurs between contractionsThe results are summed
Types of Graded ResponsesFused (complete) tetanus
No evidence of relaxation before the following contractions
The result is a sustained muscle contraction
Muscle Response to Strong StimuliMuscle force depends upon the number of
fibers stimulatedMore fibers contracting results in greater
muscle tensionMuscles can continue to contract unless
they run out of energy
Energy for Muscle ContractionInitially, muscles use stored ATP for energy
ATP bonds 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 ATP
Energy for Muscle ContractionDirect phosphorylation of ADP by creatine
phosphate (CP)Muscle cells store CP
CP is a high-energy moleculeAfter ATP is depleted, ADP is leftCP transfers energy to ADP, to regenerate
ATPCP supplies are exhausted in less than 15
seconds
Energy for Muscle ContractionAerobic respiration
Glucose is broken down to carbon dioxide and water, releasing energy (ATP)
This is a slower reaction that requires continuous oxygen
A series of metabolic pathways occur in the mitochondria
Energy for Muscle ContractionAnaerobic glycolysis and lactic acid
formationReaction that breaks down glucose without
oxygenGlucose is broken down to pyruvic acid to
produce some ATPPyruvic acid is converted to lactic acid
This reaction is not as efficient, but is fastHuge amounts of glucose are neededLactic acid produces muscle fatigue
Muscle Fatigue and Oxygen DeficitWhen a muscle is fatigued, it is unable to
contract even with a stimulusCommon cause for muscle fatigue is
oxygen debtOxygen must be “repaid” to tissue to remove
oxygen deficitOxygen is required to get rid of accumulated
lactic acidIncreasing acidity (from lactic acid) and
lack of ATP causes the muscle to contract less
Types of Muscle ContractionsIsotonic contractions
Myofilaments are able to slide past each other during contractions
The muscle shortens and movement occursIsometric contractions
Tension in the muscles increasesThe muscle is unable to shorten or produce
movement
Muscle ToneSome fibers are contracted even in a
relaxed muscleDifferent fibers contract at different times
to provide muscle toneThe process of stimulating various fibers is
under involuntary control
Effect of Exercise on MusclesExercise increases muscle size, strength,
and enduranceAerobic (endurance) exercise (biking,
jogging) results in stronger, more flexible muscles with greater resistance to fatigueMakes body metabolism more efficientImproves digestion, coordination
Resistance (isometric) exercise (weight lifting) increases muscle size and strength