CBIO 2200 1nd Edition Lecture 17 Outline of Last Lecture I. The Neuromuscular JunctionII. Myasthenia GravisIII. Electrically Excitable CellsIV. Skeletal Muscle Fiber StimulationV. Rigor MortisOutline of Current Lecture I. ATP SourcesII. Cardiac MuscleIII. Smooth MuscleIV. Neuromuscular Toxins and Paralysis V. Tension Production by Muscle ContractionVI. Behavior of Whole MusclesVII. Contraction Strength of TwitchesVIII. StimulusIX. Isometric vs. Isotonic ContractionCurrent LectureI. ATP Sourcesa. ATP supply depends on availability of:i. Oxygenii. Organic energy sources (glucose and fatty acids)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.b. Two main pathways of ATP synthesisi. Anaerobic fermentation – makes lactic acid1. ATP synthesis in the reduced presence of oxygen2. Only makes 2 ATPii. Aerobic respiration – glucose goes through glycolysis and then through respiration1. Most efficient way to make ATP 2. Makes 36, net 32c. During Exercise i. 0-6 seconds: use ATP that was availableii. 7-10 seconds: rely on phosphagen systemiii. 30-40 seconds: rely on glycogen-lactic acid systemiv. After a minute: rely on aerobic respiration; cardiovascular system has caught upd. Phosphagen systemi. Two enzyme systems control these phosphate transfers1. Myokinase – takes phosphate from ADP and add it to another ADPto make ATP2. Creatine kinase – reservoir of phosphates; removes inorganic phosphate and adding it to an ADP resulting in creatine and ATPe. Anaerobic fermentationi. Muscles shift to anaerobic fermentation1. Converts glucose to lactic acid in the presence of limited O2ii. Glycogen-lactic acid system – causes burning sensationf. Aerobic respirationi. Produce 36 ATP per glucose moleculeii. Most efficient way to make ATPII. Cardiac Musclea. Characteristicsi. Striated like skeletal muscle, but myocytes (cardiocytes) are shorter and thickerii. Intercalated discs1. Have electrical gap junctions allow each myocyte to directly stimulate its neighborsb. All of heart cells must contract in unisonc. Does not fatigue like skeletal muscles do; always pumpingd. Sarcoplasmic reticulum less developed – calcium comes from extracellular sourcee. Fibrosisf. Can contract without need for nervous stimulationi. Contains a built-in pacemaker that is independent of other body activityii. Auto-rhythmic – has its own rhythm g. Autonomic nervous system does send nerve fibers to the hearth. Uses aerobic respiration almost exclusively for production of ATPIII. Smooth Musclea. Myocyte Structure i. Myocytes have a fusiform shape1. One nucleus per cell2. No visible striationsii. Z discs are absent and replaced by dense bodiesb. Sarcoplasmic reticulum is scantyc. There are no T tubulesd. Capable of mitosis and hyperplasia so it can repair to a certain extente. Some smooth muscles lack nerve supply (independent of nerve stimulation), while others receive autonomic fibersf. Excitationi. Smooth muscle is involuntary ii. When innervated, it is innervated by autonomic nerve fibersiii. Varicosities – swelling along nerves; bathes muscle in neurotransmitter; no neuromuscular junctionsg. Contractioni. Calcium binds to calmodulin (instead of troponin) - modulates calciumii. Activates G protein which causes calcium channels to openiii. Or calcium opens by depolarizationiv. Can be stimulated by hormones, changes in pH, carbon dioxide, etc.v. Calmodulin binds to and activates myosin light chain kinase which hydrolyzes ATPvi. Now myosin can assume cocked position and bind to actin and create power strokeIV. Neuromuscular Toxins and Paralysisa. Spastic Paralysis – contraction without relaxationi. Some pesticides contain acetylcholinesterase inhibitors1. Inhibits breathing2. All muscles contract without relaxingii. Tetanus (lockjaw) is a form of spastic paralysis caused by toxin ClostridiumTetani 1. Causes muscle contraction without relaxationb. Flaccid Paralysis – muscles are limp and cannot contracti. Curare – drug that causes flaccid paralysis1. Too much can kill you2. Blocks Ach receptorii. Botulism – type of food poisoning 1. Botox injection inhibits release of AchV. Tension Production by Muscle Contractiona. Tension produced by muscle fibers depends on:i. The fiber’s resting length at the time of stimulationii. The frequency of stimulationb. We can control tension when we flex our muscles (e.g. how much you flex/try when picking up pencil vs. 10 lb weight)c. There is an optimum overlap to get maximum amount of tension (2-2.5 micrometers)i. Overly stretched – reduce amount of tension that can be producedii. Overly contracted – do no get maximum tensionVI. Behavior of Whole Musclesa. Myogram – recording of muscle contraction; recording of mechanical eventb. Twitch – 3 stagesi. Latent period – release of calcium; electrical event takes place before mechanical event startsii. Contraction phase – calcium binds to troponiniii. Relaxation phase – ATP binds to myosin causing it to release from actin; reabsorption of calciumc. Threshold – a certain amount of tension has to develop in order for muscle to contractVII. Contraction Strength of Twitchesa. Muscle fiber contraction does not follow an all or none lawb. Twitches vary in strength depending on:i. Starting lengthii. Muscles fatigue after continual useiii. Warmer muscles contract more stronglyiv. Hydration level influences cross-bridge formationv. Increasing the frequency of stimulus increases tension outputVIII. Stimulusa. Intensityb. Frequency – how often stimulus is deliveredc. Tension production by skeletal muscles depends on:i. Internal tensionii. External tension exerted by muscle fibersiii. Total number of muscle fibers stimulatedd. Recruitment (or multiple motor unit summation) – more and more muscle fibers contractinge. Strength of stimulus affects strength of contractionf. Stimulus frequency vs. muscle tensioni. If stimulus isn’t delivered very often so muscle relaxes between stimuliii. More frequent stimulus allows some relaxation but not all the way because another stimulus arrives before full relaxation; this continually increases tensioniii. Unnaturally high stimulus frequency – contract to the point where you get no relaxation at all; this would kill you; we don’t get to that point naturallyIX. Isometric vs. Isotonic Contractiona. Isometric muscle contractioni. Muscle develops tension but does not