BCMB 230 1st Edition Lecture 14 Outline of Last Lecture I.Contraction of Skeletal MuscleII.Cross Bridge CycleIII.Muscle Twitch ResponseIV.RelationshipsV.Skeletal Muscle ATP ProcessVI.FatigueVII.Controlling ContractionOutline of Current Lecture I.Types of Skeletal Muscle FiberII.Changes in Muscle SizeIII.Smooth MuscleIV.Review of Skeletal MuscleV.Compare Skeletal Muscle to Smooth MuscleVI.Muscle ToneVII.Pain (Sensory Information)Current LectureSkeletal and Smooth MuscleI. Types of Skeletal Muscle FiberSlow-oxidative Fibers-myosin-ATPase activity is low-low glycolytic enzyme activity-low glycogen content-slow rate of fatigue-depends on oxidative phosphorylation for ATP source-needs a lot of mitochondria-relies on oxygen-dependent on blood-need a lot of capillaries-fiber diameter, depends on size of cell—motor unit size is small—gives lots of control-affects contractile strength-dependent on amount of actin and myosinThese 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.Fast-Glycolytic Fibers-takes place in the cytosol-depends on glycolysis for ATP source-don’t need as much mitochondria-high glycogen content stores glucose for glycolytic process-lots of glycogen leads to a white muscle-don’t need as many capillaries-fatigues fast-can be due to lactic acid buildup-large fibers, large motor unit sizeFast-Oxidative Glycolytic Fibers-pretty much intermediate in all of them-rely on oxidative phosphorylation-lots of mitochondria-lots of capillaries-high myoglobin content—red muscle-large fiber diameters-intermediate motor unitsMuscle is a combination of the three fiber types-can enhance one fiber over anotherGenetics influence if we have more or less of each typeII. Changes in Muscle SizeHypertrophy-the individual muscle gets bigger; increase in size of cell-add more actin and myosin-body has to activate genes to increase transcription of proteins in the nucleus-adding more actin and myosin allows for more cross bridges which increases contraction-don’t increase number of cells very much-sometimes deals with cytokinese (divison of cytoplasm), not mitosis (nuclear division)-produced by high intensity exercisesHyperplasia-increase number of cells-don’t see hyperplasia in skeletal muscles-see it in cardiac and smooth muscleAtrophy-decrease in the individual cell size-don’t use the muscle, muscle gets smallerIII. Smooth Muscle-most of internal organs: stomach, uterus, bladder, blood vessels-still have cross-bridge cycles: have actin and myosin; the way we control contraction is the same-have a different arrangement of actin and myosin-don’t have sarcomeres-actin and myosin form a net-like arrangement-actin and myosin are attached to dense bodiesControl of contraction: both skeletal and smooth muscle are dependent on cytosolic Ca2+ levels-get Ca2+ into the cell-Ca2+ comes from external storage-Ca2+ binds to calmodulin-influences myosin light chain kinase (calmodulin-dependent)-enzyme that phosphorylate the myosin (activating it)-at rest, myosin is not energized-phosphorylated cross bridges bind to actin-results as tension as long as there is Ca2+Can contract smooth muscle through neurotransmitters released by autonomic neurons (sympathetic and parasympathetic), hormones, stretch, changes in chemical concentration of extracellular fluid (paracrine agents) and spontaneous electrical activityin plasma membrane of muscle cell (pacemakers)-pacemaker activity used to control rhythmic actions-smooth muscle responds to local changes; specific local chemical messengers or metabolic byproducts-stretch causes an increase in contraction -this is the same for cardiac muscle- smooth muscle-can excite or inhibit-have various levels—graded responses-inhibitory-hyperpolarize the membraneIV. Review of Skeletal Muscle -gets Ca2+ from the sarcoplasmic reticulum—largely from internal storage-function of calcium differs: binds to troponin to move tropomyosin-in skeletal muscle, myosin ATPase is always activated-get Ca2+ into the cell in skeletal muscle: action potential, goes down neuron, activate T tublules…etc.-stretch causes a decrease in contraction-only one way to influence contraction activity in skeletal muscle—neurotransmitters-only excitatory—all-or-noneV. Compare Skeletal Muscle to Smooth MuscleSkeletal-three different fiber types-each cell acts independently by the others, unless controlled by the same neuron (motor unit allows this coordination)-speed of contraction: slow to fast for skeletal muscle because of different fibers-speed depends on myosin ATPase activitySmooth-two fiber types: single unit and multi-unit-distinguished by the number of gap junctions between cells—stimulate one, stimulate the one beside it; get correlated activity-single unit has lots of gap junctions; multi-unit does not have as much-single unit-hooked together, do something to one, affects others; act as one-multi-unit- act more independently; to make them all respond, have them all receive the same stimulus-single unit-respond to neurotransmitters, hormones, stretch, pacemakers, paracrine agents-multi unit-only responds to two kinds of stimuli-neurotransmitters and hormones-speed of contraction: smooth muscle is very slow (can’t control very fast)—fatigue-resistant-fatigue not an issue for smooth muscleVI. Muscle tone-can have two different definitions-tone-low levels of tension without any external stimulation—only see it in single-unit smooth muscle-calcium channels in the membrane that are open, little bit of calcium leaks in and causes a little bit of tension (all the time)-want this because there is a little bit of a quicker response than if muscle is completely relaxed; have a little muscle toneSkeletal muscle does not have this kind of muscle toneSkeletal muscle does display muscle tone-due to a low level of nervous system stimulation(red nucleus-part of brain responsible for this; sends signal to all muscles telling them to contract a couple of motor units at a time)-when called upon, response is immediate—don’t have to contract firstSmooth muscle can undergo both kinds of muscle tone-tone as an absence of external stimuli-or some smooth muscle, especially in blood vessels, that have some contraction because you are stimulating them-blood vessels-have sympathetic toneVII. Pain (Sensory Information)Pain pathways-have receptors that tell us about tissue damage