BIOL 252 1st Edition Lecture 12 Outline of Last Lecture I. SarcomereII. Transferring contractile forces to whole musclesIII. Nerve-Muscle RelationshipIV. Muscle Contraction and RelaxationOutline of Current LectureI. RelaxationII. Muscle StrengthIII. Tension in muscle fibersIV. Length-tension relationshipV. Poll EverywhereVI. Whole-Muscle ContractionsVII. Muscle MetabolismCurrent LectureI. Relaxationa. Where does calcium go?i. Back to the SRb. How?i. Active transportii. Uses ATP to push calcium into ST against concentration gradientc. Therefore, relaxation dependent on ATPII. Muscle Strengtha. Temperaturei. If you freeze cells, molecular activity decreasesii. In our bodies, temperature constant; but if you exercise a muscle, temperature rises1. Has positive effect on contractive strength2. Warmer muscle = strongerb. pHi. Everything depends on stable pHii. Due to accumulation of lactic acid, pH decreasesc. Calcium concentrationd. Relative length of muscle cellThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.e. HydrationIII. Tension in muscle fibersa. Latent period: doesn’t seem to be anything happening for first few milliseconds i. Why is there no contraction?ii. Between time of electrical stimulation and time calcium finds troponin, no visible tensioniii. *Excitation, excitation-contraction coupling, and very beginning of contraction (there is tension, but not measurable outside of the cell)b. Contraction phasec. Relaxation phased. Why does tension build and then slowly decline? (Smooth curve)i. Release of calcium is faster than reuptakeii. Slope in contraction is greater than relaxation (diffusion vs. active transport against concentration gradient)e. Treppe: successive twitches will increase strength of twitches over timei.ii. Because there is a small amount of calcium still left over 1. Baseline calcium level slowly rises2. AP strength is still the same3. Due to warming upa. As you use muscles, temperature increases4. Baseline tension is the same f. If you stimulate that further, = wave summationi. - Incomplete tetanus (result of wave summation)ii. Results when stimuli are close together iii. Baseline of tension risesiv. Each successive twitch builds on tension of previous twitchv. How do you build tension?1. Releasing calcium from SRa. Not releasing all of it, only a portionTreppe2. Some is pulled back into SR but before we can pull back to get to tension of 0, release more calcium (2 steps forward, 1 step back)3. Increase incrementally the amount of calcium in the cellvi. Summation: Adding local potentials on top of one another to get to threshold of producing action potentialvii. Wave summation: adding TENSION on top of TENSIONviii. Know the differenceix. At the peak, reach tetanus 1. Means that we have plateaued (sustained level of contraction)2. What’s happening in the cell?3. Not substantially resorbed4. Completely releasing all of the effective calcium5. Calcium completely saturating troponin so troponin is bound with calcium => binding sites are all open6. => As we introduce more calcium, more binding sites open until allopen and cannot make stronger contraction by adding more calciumx. Fatigue1. Decrease in tension2. Category of muscle failure (there is not one specific reason)IV. Length-tension relationshipa.b. Optimal length is somewhere in the middle – easiest to contractV. Which of the following does NOT describe how your body controls strength of muscle contraction?a. Changing intracellular calcium levels - YESb. Changing muscle temperature – NOi. Temperature affects strength but doesn’t control itii. Do not intentionally find a way to increase temperature to control strengthc. Activating more/fewer motor unitsi. What’s a motor unit?ii. More motor units => more muscle contracting => more strength iii. So YESd. Change frequency of neuronal action potentialsi. What is the effect on a muscle?ii. More contraction (more calcium, more APs)iii. So YESe. Changing number of myosin binding sitesi. More cross-bridges (stronger contraction)VI. Whole-Muscle Contractionsa. Contraction is generation of force, tensionb. Isometric contractioni. Muscle develops tension but does not shortenii. No movementiii. Ex: carrying a coffee cup c. Isotonic contraction – tension remains constant but there is movementi. Isotonic concentric contraction1. Muscle shortens2. More than 5kg force generated for 5kg weight3. Ex: picking baby upii. Isotonic eccentric contraction1. Muscle lengthens2. Less than 5kg force generated for 5kg weight3. Ex: putting baby downVII. Muscle Metabolisma. All muscle contraction depends on ATPb. Where does ATP come from?i. Glycolysis1. Generate 2 ATP NET molecules + pyruvic acid2. + O2 => aerobic respirationii. Aerobic respiration1. WITH OXYGEN2. Glucose molecule generates 36 ATP3. + 2 from glycolysis = 38 total ATP4. *Without oxygen – anaerobic respiration a. Examples: very strenuous exercise for short time or exercise for a long amount of time 5. More sufficient to have oxygen aroundiii. Phosphagen system1. Regeneration of ATP2. ADP 3. Myokinase (enzyme)a. Kinase phosphorylates 4. When muscles are active, myokinase takes ADP => AMPa. Takes one phosphate awayb. Takes extra P and puts it on ADP => ATP5. 2 ADP => ATP + AMP6. Creatine kinasea. Creatine phosphate => creatine kinase when removes Pb. Adds to ADPc. => Creatine +