CBIO 2200 1nd Edition Lecture 17 Outline of Last Lecture I The Neuromuscular Junction II Myasthenia Gravis III Electrically Excitable Cells IV Skeletal Muscle Fiber Stimulation V Rigor Mortis Outline of Current Lecture I ATP Sources II Cardiac Muscle III Smooth Muscle IV Neuromuscular Toxins and Paralysis V Tension Production by Muscle Contraction VI Behavior of Whole Muscles VII Contraction Strength of Twitches VIII Stimulus IX Isometric vs Isotonic Contraction Current Lecture I ATP Sources a ATP supply depends on availability of i Oxygen ii 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 II b Two main pathways of ATP synthesis i Anaerobic fermentation makes lactic acid 1 ATP synthesis in the reduced presence of oxygen 2 Only makes 2 ATP ii Aerobic respiration glucose goes through glycolysis and then through respiration 1 Most efficient way to make ATP 2 Makes 36 net 32 c During Exercise i 0 6 seconds use ATP that was available ii 7 10 seconds rely on phosphagen system iii 30 40 seconds rely on glycogen lactic acid system iv After a minute rely on aerobic respiration cardiovascular system has caught up d Phosphagen system i Two enzyme systems control these phosphate transfers 1 Myokinase takes phosphate from ADP and add it to another ADP to make ATP 2 Creatine kinase reservoir of phosphates removes inorganic phosphate and adding it to an ADP resulting in creatine and ATP e Anaerobic fermentation i Muscles shift to anaerobic fermentation 1 Converts glucose to lactic acid in the presence of limited O 2 ii Glycogen lactic acid system causes burning sensation f Aerobic respiration i Produce 36 ATP per glucose molecule ii Most efficient way to make ATP Cardiac Muscle a Characteristics i Striated like skeletal muscle but myocytes cardiocytes are shorter and thicker ii Intercalated discs 1 Have electrical gap junctions allow each myocyte to directly stimulate its neighbors b All of heart cells must contract in unison c Does not fatigue like skeletal muscles do always pumping d Sarcoplasmic reticulum less developed calcium comes from extracellular source e Fibrosis f Can contract without need for nervous stimulation i Contains a built in pacemaker that is independent of other body activity ii Auto rhythmic has its own rhythm g Autonomic nervous system does send nerve fibers to the heart h Uses aerobic respiration almost exclusively for production of ATP III IV V Smooth Muscle a Myocyte Structure i Myocytes have a fusiform shape 1 One nucleus per cell 2 No visible striations ii Z discs are absent and replaced by dense bodies b Sarcoplasmic reticulum is scanty c There are no T tubules d Capable of mitosis and hyperplasia so it can repair to a certain extent e Some smooth muscles lack nerve supply independent of nerve stimulation while others receive autonomic fibers f Excitation i Smooth muscle is involuntary ii When innervated it is innervated by autonomic nerve fibers iii Varicosities swelling along nerves bathes muscle in neurotransmitter no neuromuscular junctions g Contraction i Calcium binds to calmodulin instead of troponin modulates calcium ii Activates G protein which causes calcium channels to open iii Or calcium opens by depolarization iv Can be stimulated by hormones changes in pH carbon dioxide etc v Calmodulin binds to and activates myosin light chain kinase which hydrolyzes ATP vi Now myosin can assume cocked position and bind to actin and create power stroke Neuromuscular Toxins and Paralysis a Spastic Paralysis contraction without relaxation i Some pesticides contain acetylcholinesterase inhibitors 1 Inhibits breathing 2 All muscles contract without relaxing ii Tetanus lockjaw is a form of spastic paralysis caused by toxin Clostridium Tetani 1 Causes muscle contraction without relaxation b Flaccid Paralysis muscles are limp and cannot contract i Curare drug that causes flaccid paralysis 1 Too much can kill you 2 Blocks Ach receptor ii Botulism type of food poisoning 1 Botox injection inhibits release of Ach Tension Production by Muscle Contraction a Tension produced by muscle fibers depends on i The fiber s resting length at the time of stimulation ii The frequency of stimulation VI VII VIII b 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 produced ii Overly contracted do no get maximum tension Behavior of Whole Muscles a Myogram recording of muscle contraction recording of mechanical event b Twitch 3 stages i Latent period release of calcium electrical event takes place before mechanical event starts ii Contraction phase calcium binds to troponin iii Relaxation phase ATP binds to myosin causing it to release from actin reabsorption of calcium c Threshold a certain amount of tension has to develop in order for muscle to contract Contraction Strength of Twitches a Muscle fiber contraction does not follow an all or none law b Twitches vary in strength depending on i Starting length ii Muscles fatigue after continual use iii Warmer muscles contract more strongly iv Hydration level influences cross bridge formation v Increasing the frequency of stimulus increases tension output Stimulus a Intensity b Frequency how often stimulus is delivered c Tension production by skeletal muscles depends on i Internal tension ii External tension exerted by muscle fibers iii Total number of muscle fibers stimulated d Recruitment or multiple motor unit summation more and more muscle fibers contracting e Strength of stimulus affects strength of contraction f Stimulus frequency vs muscle tension i If stimulus isn t delivered very often so muscle relaxes between stimuli ii More frequent stimulus allows some relaxation but not all the way because another stimulus arrives before full relaxation this continually increases tension iii 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 naturally IX Isometric vs Isotonic Contraction a Isometric muscle contraction i Muscle develops tension but does not shorten ii No movement just holding something up iii Can have different tensions b Isotonic muscle contraction i Muscle is changing length ii Tension remains
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