Download Different Types of Muscle Fibers - Fundamentals of Physiology | BMS 360 and more Study notes Biology in PDF only on Docsity! 15 February Figure 9.28: different types of muscle fibers Slow-oxidative fibers – smallest Fine control Fast-oxidative fibers Intermediate sized Fast-glycolytic fibers – largest Pick something up Use small muscle fibers at first, then recruit intermediate fibers (more force), then recruit large muscle fibers (maximal force) Figure 9.25 Slow-oxidative Lots in legs Long-distance running Usable for a long time without fatiguing Maintainable force Eventual build-up of lactic acid, depletion of glycogen Takes time to refill glycogen reserves Fast-oxidative 10 minutes Also present in legs Fast-glycolytic Use for weight lifting Depleted of glycogen after a few minutes Buildup of K+ in T-tubules Takes time to clear tubules Ionic gradient lost, action potential in T-tubule fails Low intensity long-duration exercise Swim, run, &c. over many weeks Increase # of mitochondira Increase # of capillaries Increase endurance Small decrease in fiber diameter and muscle strength Increase in number of fast-oxidative fibers (red muscles) Decrease in number of fast-glycolytic fibers (white muscle) Reverts when exercise is stopped Short duration, high intensity exercise Weight lifting, &c. over many weeks Fast glycolytic fibers increase in diameter and muscle strength increases Increased synthesis of myosin and actin filaments Increased synthesis of glycolytic enzymes Muscles fatigue rapidly Increase in number of fast glycolytic fibers Decrease in number of fast oxidative fibers Reverts when exercise is stopped Figure 9.27 Figure 9.34 Signal → increase in Ca++ within cell Ca++ ion channels Calmodulin activated Myosin light-chain kinase activated by Ca++/calmodulin Pi added to crossbridges No troponin in smooth muscle Cross-bridges bind as soon as they are phosphorylated Contractions continue until Ca++ pumped out Figure 9.38 Single-unit smooth muscle Neuron runs through with varicosities (which release NT) Coupled to other cells through gap junctions, Ca++ flows through Single-unit smooth muscle Uterus, small-diameter blood vessels, etc. Gap junctions couple cells together Depolarization spreads from cell to cell All the connected cells can respond together as a group Autonomic nerves can regulate the frequency of pace-maker cells (these are coupled to the other cells) Responsive to stretch Responsive to hormones and other factors Figure 9.37 Multiunit All fire together, each by a varicosity Dependent on sympathetic/parasympathetic nerves No gap junctions Multi-unit smooth muscle Lungs, large arteries, etc. Few gap junctions Each muscle cell acts independently Most have individual contact with autonomic varicosities Generally an action potential does not fire Depolarization (below threshold) is sufficient for contraction Not responsive to stretch Responsive to hormones
