Lec27
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1. Muscle fibers are stimulated at different frequencies, producing different types of contractions. Low frequencies cause individual twitches, while higher frequencies produce temporal summation and then incomplete and complete tetanus. 2. ATP is required for muscle contraction and is synthesized through different pathways including creatine phosphate breakdown, glycolysis, and the Krebs cycle. Glycolysis produces ATP rapidly but also lactic acid, while the Krebs cycle provides more sustained energy production. 3. Muscle fibers come in two main types - white/fast twitch fibers that contract rapidly but fatigue quickly using glycolysis, and red/slow twitch fibers that contract slowly but are fatigue resistant using the Krebs cycle.
Lec27
- 1. Degree of muscle stretch (The Effect of Sarcomere Length on Tension)
- 2. Change the strength of stimulusThe stimulus intensity increases , more and more motor units are stimulated, and thus the strength of muscle contraction increases
- 3. Effects of frequency of Stimulation
- 4. Twitch and Treppe ContractionsMuscle stimulation at variable frequencieslow frequency (up to 10 stimuli/sec)- each stimulus produces an identical twitch responsemoderate frequency (between 10-20 stimuli/sec)each twitch has time to recover but develops more tension than the one before (treppe phenomenon)calcium was not completely put back into SR
- 5. Incomplete and Complete TetanusHigher frequency stimulation (20-40 stimuli/second) generates gradually more strength of contraction each stimuli arrives before last one recoverstemporal summation or wave summationMaximum frequency stimulation (40-50 stimuli/second) muscle has no time to relax at alltwitches fuse into smooth, prolonged contraction called complete tetanus
- 6. TREPPEALL PHASES OF MUSCLE CONTRACTIONARE PRESENT AND HAVE NOT BEEN ALTERED.
- 7. TEMPORAL (wave) SUMMATIONIF TWO IDENTICAL STIMULI ARE DELIEVERED TO A MUSCLE IN RAPID SUCCESSION, THE SECOND CONTRACTION WILL SUMMATE WITH THE FIRST.THE RELAXATION PHASE HAS BEEN SHORTENED.
- 8. INCOMPLETE TETANUSIF THE STIMULUS STRENGTH IS HELD CONSTANT AND THE MUSCLE IS STIMULATED AT AN INCREASINGLY FASTER RATE, INCOMPLETE TETANI RESULTS.
- 9. COMPLETE TETANUSWHEN ALL EVIDENCE OF MUSCLE RELAXATION DISAPPEARS AND THE CONTRACTIONS FUSE INTO A SMOOTH, SUSTAINED CONTRACTION, COMPLETE TETANUS RESULTS.
- 10. FatigueFatigue is defined as the decrease in muscular activity due to repeated stimuli. When stimuli are applied repeatedly, after some time, the muscle does not show any response to the stimulus. This due to built up of acidic compound which affect protein functioning, lack of ATP and ionic imbalances
- 11. Functions of ATP in Skeletal Muscle ContractionHydrolysis of ATP by myosin - energizes the cross-bridges, providing energy for force generation.Binding of ATP to myosin - dissociates cross-bridges bound to actin.Energizes Capumps that actively transport Ca back into the sarcoplasmic reticulum- Lowers cytosolic Ca level leading to relaxationRuns the Na+-K+ pump in the sarcolemma- maintains the resting membrane potential of the sarcolemmaMuscle Metabolism
- 12. ATP: Compose of Adenine nucleotide, two phosphate groups, attached by high energy phosphate bond
- 13. ATP SynthesisMuscle cells uses three processes to synthesize ATPHydrolysis of creatine phosphateGlycolysisKrebs cycle and oxidative phosphorylation
- 14. ATP Synthesis (hydrolysis of creatine phosphate)Creatine phosphate (CP): Organic compound in muscle cells serves as source of energyMost rapid method of ATP generationADP + CP creatine kinase C + ATPThe amount of CP is limited and rapidly depletedOnly 1 ATP per CP usedCP (creatine phosphate) regenerated during resting conditions (ATP + C CP + ADP)
- 15. ATP Synthesis (Glycolysis)Glucose is the major source of energy for synthesizing ATP. Glucose available to muscle from two different sourcesGlucose enter the body directly from the bloodGlucose is produced by hydrolysis of glycogen that stored in muscle cells
- 16. ATP Synthesis (Glycolysis)Glucose is broken down in glycolysisEnd product of glycolysis include:2 ATP moleculePyruvic acidIn the absence of O2, pyruvic acid is converted into lactic acid (the end product of anaerobic pathway) Excess lactic acid builds up and caused muscle fatigueIn the presence of O2, aerobic pathway (Krebs cycle) proceeds, pyruvic acid converted to acetyl CoAThe end products: CO2, H2O and 36 molecule ATP
- 17. O2 enter the muscle cells from two sources:O2 enter the muscle cells directly from the bloodO2 stored in myoglobin, an oxygen binding proteins
- 18. Muscle Metabolism: Energy for ContractionFigure 9.18
- 19. Physical ActivitiesSome use mainly aerobic respiration.
- 20. Others use mainly anaerobic respiration.
- 21. Most use a combination of the two.100%Marathon95%10,000 m83%5,000 m60%1,500 m50%800 m20%400 mBasketball players use both systems 10%200 mLess than 1%100 m
- 22. Oxygen DebtOxygen Dept: The oxygen required to completely oxidized lactic acid formed and to replenish the depleted stores of ATP and creatine phosphateFor a muscle to return to a resting state:Additional oxygen to rebind to myoglobinLactic acid must be converted to pyruvic acid which enter krebs cycle producing ATPATP use to rephosphorylate creatine into CP Glycogen synthesize from glucose
- 23. Oxygen DebtHow do sprinters pay back their oxygen debt at the end of a race?Sprinters will continue to breathe more deeply and rapidly for a number of minutes at the end of their race. This will enable them to pay back the oxygen debt, and allow lactic acid levels to fall.
- 24. Variations in muscle fiber typeThere are two types of muscle cells which differ in size and colorationWhite muscle cellsRed muscle cellsThese structural differences relate to their method of metabolism
- 25. Features of white muscle fiberLarge in diameterLight in color due to reduced myoglobinFew mitochondriaFew capillariesHigh glycogen contentMainly use glycolysis to synthesize ATPRapid cross bridge cycling results in fast contractionsCalled fast twitch glycolytic fiberFatigue rapidly due to build up of lactic acid and depletion of glycogen
- 26. Features of red muscle fiberHalf diameter of white muscle fiberDark red in color due to myoglobinSurrounded by many capillariesNumerous mitochondriaLow glycogen contentCross bridge occur slowlyCalled slow twitch oxidative fiber Synthesize ATP by krebs cycleFatigue resistant