mJuly 1 2013 Lecture 3 Ch 48 Sections 48 1 48 3 Pre read Ch 51 Sections 51 1 51 4 1 Describe the structure of muscle cells and tissues 2 Explain muscle contraction including the sliding filament model and use this model to 3 Compare and contrast muscle contraction among the different muscle type skeletal explain rigor mortis cardiac smooth 4 Explain factors that contribute to muscle performance 5 Differentiate between skeletal types and how their muscles and bone interact 6 Describe the structure of and process of building bone There are three types of muscle Skeletal Voluntary some involuntary Striated Has repeated structures within the cells Multinucleate Cardiac Involuntary Striated Uni nucleate Branched with inter palleted disks Smooth Involuntary Not striated Uni nucleate Arranged in sheets sometimes alternating sheets Found lining organs and vessels Sensitive to stretch Each muscle fiber is a single cell skeletal muscle Myofibrils Highly ordered assemblages of thick myosin and thin actin filaments Multi or uni nucleate Cytoskeleton Microfilaments Can contain things capable of movement Made up of strands of the protein actin Often interact with strands of other proteins Motor proteins Myosin Sarcomeres Units of contraction Make up myofibrils Contains actin and myosin Actin thin filament Myosin thick filament One Z line to another Z line is one sarcomere Muscles Made up of bundles of muscle fibers Striations appear due to repeated sarcomeres Microfilament Microfilament Actin Myosin Z line M band Where the actin attaches Piece in the center of the sarcomere Holds the myosin in place I band Actin only The length of the myosin filament Still contain both actin and myosin A band H zone Myosin only Titin Piece in the middle From the end of one piece of myosin to the end of the next piece of myosin Attaches to the Z line and maintains the position of the myosin Determines the muscles flexibility Protein Determines length of sarcomere and resting length of muscle All muscle cells contract using sliding filaments Titin Myosin Motor protein thick filament Made of several motor proteins Requires ATP to change shape Attaches to and shifts actin Actin Attached to Z line on both sides Slides along myosin towards the middle pulls ends together Thin filament Shortens sarcomere when pulled towards the middle Portions never overlap H I Actin and myosin interact to contract muscle Troponin Three subunits Each subunit has a binding site One binds to actin One binds to tropomyosin One binds to calcium Tropomyosin Myosin head Linear polypeptide chain Globular head Many chains with heads and tails Head grabs the actin Recognizes specific sites Protein rope like structure wrapped around actin Either blocks or reveals binding site on actin where myosin attaches When bound to actin it changes shape and causes actin to move ATP When myosin binds to actin it must bind to ATP Then hydrolyzes ATP ADP P Releases actin Rigor mortis Myosin molecules are bound to actin and stay that way Myosin cannot release actin Muscles are stiff In the presence of Ca muscle contracts Calcium comes into the cell and binds to troponin This causes troponin to pull trypomyosin out of the way Allows binding of actin and myosin Stays bound until another ATP comes in and releases it Ca is released from the sarcoplasmic reticulum after neuron stimulation skeletal Acetylcholine Neurotransmitter that binds to the receptors found on the muscle Causes sodium to rush into the cells Depolarizes muscle Causes SR to release calcium Aids in muscle contractions Receptor T tubule Tubes that transfer action potential into the muscle Transmit across the whole muscle fiber When it sends messages it cases sarcoplasmic reticulum to release calcium Neuromuscular junction Sarcoplasmic reticulum Modified endoplasmic reticulum Stores calcium Neuron Depolarized Releases neurotransmitter Single muscle twitches are summed into a single graded contraction Twitch the minimum unit of contraction of a muscle fiber Twitches in quick succession have a summed effect greater effect when more twitches Motor unit Tetanus Neuron that is synapsing with many muscle fibers Summed twitches bring the muscle fiber to a maximum contraction known as tetanus Tetanus is sustained by a high rate of stimulation Length of occurrence is dependent on ATP presence Long lasting or sustained reaction Smooth muscle does not use troponin or tropomyosin Stretch Signal for smooth muscle to start working Sympathetic and para sympathetic Stimulated by autonomic nervous system Norepinephrine situation dependent Stimulates Relaxes Digestive system has multiple receptors for norepinephrine Calmodulin Second messenger approach for binding Calcium is still used Calcium binds to calmodulin Complex binds to myosin kinase Happens in response to action potentials hormones stretching Myosin kinase Phosphorylates myosin once bound to calmodulin Leads to power stroke Myosin phosphatase De phosphorylates myosin Leads to release of actin Cardiac muscle is striated uninucleate and pacemaker cells fire spontaneously Change of negative to positive charge inside cell Depolarization Intercalated disks Support Gap junctions Used for quick communication between cells Unstable resting potential of pacemaker cells Slow Na channels Sinoatrial node In right atrium Also known as pacemaker Depolarization occurs and sodium channels are supposed to close in order to get resting potential back However they are leaky Sodium is always leaking into heart Heart can generate its own action potential When calcium enters potassium leaves at a much greater rate Purkinje fibers Passes message along Wrap around ventricles Part of conducting fibers Systole Contraction occurs Diastole Recovering from contraction There are two different types of muscle fibers Fast twitch Can generate maximum tension quickly but also fatigue quickly High ATP ase activity Recycle actin and myosin cross bridges quickly Very few mitochondria Little to no myoglobin Myoglobin holds oxygen well Go through just glycolysis Slow twitch Better adapted for sustained aerobic activities More mitochondria in cells Do a lot of oxidative metabolism Lots of myoglobin Go through complete cellular respiration Force generated depends on sarcomere length Intermediate length The time that you can generate the most force Cannot generate force if myosin and actin aren t overlapping or are overlapping too much Muscle soreness results from tissue damage not from lactic