BIO 251 1st Edition Lecture 12 Outline of Last Lecture I. Introduction to all muscles a. Skeletal b. Cardiac c. smoothII. Structure of skeletal muscle a. Muscle fiber b. Thick filamentsc. Thin filamentsIII. Molecular basis of contractiona. Cross bridgeIV. Birth controlV. Rigor Mortis Outline of Current Lecture I. Events in muscle contraction II. Factors of whole muscle tensionIII. Muscle metabolism & fiber types a. Skeletal fiber types IV. Control of motor movement These 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.Current Lecture-Events in Muscle contraction oWhole muscle is composed of muscle fibers bundled together by CT & attached to bonesby tendons -Contraction of enough muscle fibers results in mvmt of bone or limboSingle AP produces a brief weak contraction (twitch) -Single AP doesn’t normally occur-Muscle fibers organized so they can function to produce contractions stronger than twitch oTiming of contraction (12.11)-Latent period -Time between initiation of stimulation & start of contraction-AP occurs during this time -1-2 msec-Contraction time -Time between onset of contraction & peak tension -Continues until all Ca++ removed -50 msec-Relaxation time -Time between peak tension & complete relaxation -50 msec or more-Total contractile response to single AP is 100 msec or more, compared to 2 msecAP that produced response -Factors influencing whole muscle tension oFrequency of stimulation (voluntary control)-Twitch summation (12.6)-Single AP-single twitch -2 AP close together-summation of twitch -Multiple AP close together-summation of twitch -Tetanus-many rapid stimuli prevent muscle relaxation -Contraction of max strength -Increased AP=max tension -All fibers recruited, asynchronous contracting isnt possible, fatigue eventually occurso# muscle fibers contracting within a muscle (12.18)-Motor unit recruitment (under voluntary control)-External eye muscles~12 muscle fibers/motor unit -Leg muscles ~2000 muscle fibers/motor unit -Length of fiber at onset of contraction (12.17)-Optimal resting length of muscle gives max tension -Non-optimal resting lengths give sub max tension -Diameter of muscle -Bigger muscle cell can generate more force -Muscle metabolism & fiber types oATP required for muscle contraction oATP sources (12.22 & 12.23)-Creatine phosphate is 1st energy storehouse tapped-Energy reserves in resting muscle stored in creatine phosphate (5x as much in muscle as ATP)-When energy needed for contraction-Creatine phosphate + ADP <-->creatine + ATP (requires activity of enzyme creatine kinase) -Rested muscle, creatine phosphate is ready to go, and that’s what you use as an ATP source during burst activity ( 1 min or less)-Glycolysis + Krebs Cycle + Oxidative Phosphorylation -Mitochondria in muscle require oxygen & duel to produce ATP -Can make ~38 ATP/glucose this way-Slow compared to creatine phosphate-Can be done during aerobic exercise -O2 is supplied by blood, during aerobic exercise body maximizes O2 delivery to muscles -Anaerobic pathways (glycosis alone)-Can make ATP fast -Only makes 2 ATP/glucose-Rapidly depletes fuel supply (glycogen)-Produces lactic aid -Contribute to muscle soreness & fatigue -Lead to metabolic acidosis (bad)-Contributes to fatigue -BOTTOM LINE: anaerobic exercise possible for short time oFatigue (12.26)-Muscle fatigue -Asynchronous recruitment of motor units used to limit muscle fatigue -Fatigue occurs when muscle cant respond to stimulation w/ same degree of contractile activity, b/c of lactic acid accumulation & depletion of energy reserves -Neuromuscular fatigue-Motor neurons cant make Ach fast enough -Central fatigue-Psychological-not well understoodoOxygen consumption elevated during recovery from exercise -Oxygen debt -Contractile energy debt from nonoxidative ATP sources needs to be repaid during recovery -Creatine phosphate resynthesized -Lactic acid metabolized -Replenish glycogen stores -Recovery from general metabolic disturbance -All chem rxns still speeded up -Still high levels of epioSkeletal muscle fiber types -3 types (12.1)-Slow oxidative (type I) fibers-Fast oxidative (type IIA) fibers-Fast glycolytic (type IIB) fober -Most muscles have all 3 types -Motor unit is composed of all one type of fiber-Within a muscle, fast oxidative & fast glycolytic can interconvert over time, depending on how muscle is trained -Hypertrophy -Increase in muscle fiber diameter -Hyperplasia -Increase in muscle fiber number (usually occurs by splitting muscle fibers, RARELY happens)-Control of motor movement o3 levels of input control motor neuron output -Spinal reflexes-Primary motor cortex (cerebral cortex)-Other cortical & subcortical regions of brain (basal nuclei, cerebellum, thalamus,and others) send signals to primary motor cortex and/or brain stem , each of which can then directly control motor