KIN 292 1nd Edition Lecture 20Outline of Last Lecture I. 12.1 Skeletal Muscle StructureII. 12.2 The Mechanism of Force Generation in MuscleIII. 12.3 The Mechanics of Skeletal Muscle Contraction (covered in lab)IV. 12.4 Skeletal Muscle Metabolism – part 1Outline of Current Lecture I. 12.4 Skeletal Muscle Metabolism – continuedII. 12.5 Control of Skeletal Muscle ActivityIII. 12.6 Smooth and Cardiac Muscle previewCurrent LectureMuscle 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 contentAdaptations to Exercise TrainingEndurance TrainingThese 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 fastStrength 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 isoformCreatine 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 offSize 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 intensity12.5 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 forceMuscle 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 fiberso Contractile cells of the muscle spindleo Innervated by gamma motor neurons – small diameter and slow conduction velocity (Table 7.4)- Extrafusal fiberso Contractile cells of the muscleo 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 muscleCardiac 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 timeSingle-unit smooth muscle - Most common typeLocation: Intestinal tract; Blood vessels; Respiratory tractMuscle fibers connected by gap junctions and contract together (synchronously) as a single