BCMB 230 1st Edition Lecture 14 Outline of Last Lecture I Contraction of Skeletal Muscle II Cross Bridge Cycle III Muscle Twitch Response IV Relationships V Skeletal Muscle ATP Process VI Fatigue VII Controlling Contraction Outline of Current Lecture I Types of Skeletal Muscle Fiber II Changes in Muscle Size III Smooth Muscle IV Review of Skeletal Muscle V Compare Skeletal Muscle to Smooth Muscle VI Muscle Tone VII Pain Sensory Information Current Lecture Skeletal and Smooth Muscle I Types of Skeletal Muscle Fiber Slow 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 myosin 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 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 size Fast 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 units Muscle is a combination of the three fiber types can enhance one fiber over another Genetics influence if we have more or less of each type II Changes in Muscle Size Hypertrophy 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 exercises Hyperplasia increase number of cells don t see hyperplasia in skeletal muscles see it in cardiac and smooth muscle Atrophy decrease in the individual cell size don t use the muscle muscle gets smaller III 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 bodies Control of contraction both skeletal and smooth muscle are dependent on cytosolic Ca 2 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 activity in 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 membrane IV 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 none V Compare Skeletal Muscle to Smooth Muscle Skeletal 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 activity Smooth 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 muscle VI 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 tone Skeletal muscle does not have this kind of muscle tone Skeletal 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 first Smooth 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 tone VII Pain Sensory Information Pain pathways have receptors that tell us about tissue damage name ability of receptors to adapt to pain is not particularly strong slow adapting can block the pain