KIN 292 1nd Edition Lecture 20 Outline of Last Lecture I 12 1 Skeletal Muscle Structure II 12 2 The Mechanism of Force Generation in Muscle III 12 3 The Mechanics of Skeletal Muscle Contraction covered in lab IV 12 4 Skeletal Muscle Metabolism part 1 Outline of Current Lecture I 12 4 Skeletal Muscle Metabolism continued II 12 5 Control of Skeletal Muscle Activity III 12 6 Smooth and Cardiac Muscle preview Current Lecture Muscle Fiber Type Most muscles have a range of fiber types identified by their contractile and metabolic characteristics All fibers within a given motor unit are the same type Force generating capacity is a function of fiber diameter and number of fibers per motor unit More crossbridges more force Red color comes from greater amount of iron from mitochondria cytochromes and myoglobin Myoglobin helps speed transport of O2 to mitochondria Causes of fatigue in response to high stimulus intensities include increased ADP and acidity lactic acid production decreases pH Both of these slow crossbridge cycling Much smaller change in ADP and pH in slow oxidative compared to fast glycolytic because slow oxidative is using ATP slower and has much greater mitochondria content Adaptations to Exercise Training Endurance Training 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 Diameter may decrease in some fibers to decrease O2 diffusion distance more important than ability to generate force Capillary density increases Increases delivery of O2 and removal of heat and waste products such as lactic acid More mitochondria Myosin isoform doesn t change slow stays slow fast stays fast Strength Training Hypertrophy of all muscle fibers increase in diameter more crossbridges number size of myofibrils per fiber No hyperplasia increase fiber number Decrease capillary density and mitochondria No change in myosin isoform Creatine Supplement are very popular and legal Creatine supplements might increase muscle mass and strength Controversial Some studies report gains some report no gains Thus at best you can expect small gains How does it work Some of the creatine taken up by muscles is converted to creatine phosphate by mass action Remember this from Ch 3 ADP CrP ATP Cr Keq 5 10 100 where brackets mM conc 0 02 25 If Cr in muscle is raised by 3 5 mM 2 5 mM will be converted to CrP according to the equilibrium constant Keq 5 0 11 100 0 2 27 5 The small CrP energy reserve is increased which can allow for a harder work out Possibly more repetitions before fatigue and faster recovery Some reports indicate it increases proteins synthesis but controversial Does not increase endurance only strength Also increases water content in muscles This makes muscles look bigger but can lead to dehydration So drink lots of water Many reported side effects are likely due to taking too much creatine Only need about 5 grams day Long term effects not known Recommended that you cycle few weeks on few weeks off Size Principle for Fiber Recruitment MUs with smaller cell bodies somas will be depolarized first thus used first Require low stimulus strength Slow twitch MUs have smaller somas than fast Fast oxidative smaller somas than fast glycolytic Daily life Slow twitch recruited Normal walking speed recruits only a few motor units per step To recruit higher threshold fast fibers must increase stimulus strength to neurons Accomplished by increasing work exercise intensity 12 5 Control of Skeletal Muscle Activity Muscle Receptors for Coordinated Activity Muscle spindle Detects changes in muscle length Small and located throughout muscle Golgi tendon organ Detects muscle tension Sensory capsules within tendons a great place to monitor muscle force Muscle Spindle stretch reflex Stretch signals excitatory information to agonist muscle and inhibitory information to antagonistic muscle Very relevant in fast sport related movement pitching example When muscle is stretched intrafusal fibers are stretched increasing activity in Tyoe Ia and II afferent fibers Intrafusal fibers o Contractile cells of the muscle spindle o Innervated by gamma motor neurons small diameter and slow conduction velocity Table 7 4 Extrafusal fibers o Contractile cells of the muscle o Innervated by alpha motor neurons big fast During contraction alpha and gamma are activated at the same time however since gamma has a slower conduction velocity extrafusal fibers innervated by alpha motor neurons contract first This initially results in a decrease in afferent activity as shown in previous slide contracted muscle Within milliseconds the intrafusal fibers contract to equivalent amount as extrafusal fibers thus removing the slack and returning to normal monitoring activation rate Tendon stretch activates the GTO Reflex inhibition of muscle via type Ib afferent neurons Protection against overactivity of muscle Cardiac Muscle Like skeletal muscle striated with same sarcomeres Troponin tropomyosin regulation Gap junctions within intercalated disks Has Pacemaker cells that depolarize and contract without any nerve stimulation Innervated by autonomic nervous system Ca2 comes from extracellular fluid and sarcoplasmic reticulum Action potential lasts almost as long as tension next slide No summation due to long refractory period next slide 100 oxidative energy metabolism all the time Single unit smooth muscle Most common type Location Intestinal tract Blood vessels Respiratory tract Muscle fibers connected by gap junctions and contract together synchronously as a single unit