KINS Unit 3 Lecture 4 Study Guide Muscle Tissue Organization Organization of Fascicles and Fibers within muscle influences function 1 Parallel or longitudinal Fascicles run parallel to longitudinal axis a PARALLEL ARRANGEMENT MUSCLE IS RELATIVELY WEAK i Contracts over a greater distance ii Bones move over greater range at greater speed Strap like Fascicles parallel to each other Fusiform Fascicles slightly rounded or spindle shaped Ex Biceps Ex Sartorius Rectus Abdominus 2 Pennate or Penniform a Fascicles set at an angle to the tendon appear feather like Unipennate Fascicles approach tendon from one side only Ex Semimembranosis Bipennate Fascicles approach central tendon from both sides Ex Rectus Femoris Multipennate Fascicles arranged among multiple tendons Ex Deltoid 3 Convergent a Fascicles converge toward a single tendon from a broad origin Ex Pectoralis Major Latissimus Dorsi Pennate Convergent muscles contract over a limited range Favor increased force Produce more tension 4 Circular Fascicles arranged in a circle about structures such as mouth or eyes ex Orbicularis oculi Chemical Composition of Muscle 75 H2O 20 protein 3 major proteins 1 Actin 2 Myosin 3 Myoglobin Glycogen polysaccharide 5 salts lipids other materials Microscopic Structure of Muscle Nuclei a Pigment with strong affinity for O2 transfer O2 from blood to mitochondria o Multi nucleated fusion of many cells o Nuclei in periphery of fiber just under sarcolemma Mitochondria Myofibrils o Abundance of mitochondria o Energy demands of muscle contraction structure function o Longitudinal in sarcoplasm organized into columns o Contractile elements of muscle 80 of fiber s volume o Appear as alternating bands of light dark areas Muscle striations result from alignment of proteins Myosin Thick filament with rod like tail and 2 globular heads cross bridges that interact with actin during contraction process o Distinctive structure related to role in contraction process o Myosin myofilament contains around 200 500 bundled molecules of myosin Tails from central portion Cross bridges face outward in opposite directions Cross bridges arranged in 6 rows on myosin myofilament interact with 6 actins Actin Thin filament o Actin myofilament double strand of actin molecules twisted together 2 proteins associated with actin 1 Tropomyosin rod shaped protein a Spiral in groove between 2 strands of actin molecules 2 Troponin complex of 3 globular proteins a Located along actin myofilament Two intertwined strands fibrous F actin o Globular G actin with an active site Groove holds tropomyosin molecules each blocking 6 or 7 active sites of G actins One small Ca binding troponin molecule on each tropomyosin molecule o Titan Elastic filament Giant protein Passes through myosin from Z disc M line Extensible region of I band o Returns fiber to resting shape after stretch o Helps keep myosin and actin aligned A Band Dark area where actin and myosin overlap determined by length of myosin 6 ACTIN 1 MYOSIN 3 MYOSIN 1 ACTIN H Zone Light area within A Band contains only myosin M Line Line within H Zone resulting from fine strands of fibrous protein Connect adjacent myosin filaments hold them in place Filamentous network of fibrous protein forming disk like structure I Band Light area contains only actin Z Disc Z Line Dark line through I band for actin attachment Sarcomere Region between Z Lines Functional contractile unit of muscle fiber Sarcoplasmic Reticulum elaborate form of smooth ER forming sleeves around each myofibril interconnecting tubules parallel to myofibrils o End in lateral channels o Terminal Cistarnae Channels at A I band junction located above and below Z disc o SR and terminal cisternae contain high concentration of Ca important in contraction process T tubules extensions of the sarcolemma at the level of each Z disc o Sarcolemma invaginates into fiber and forms a hollow elongated tube called T tubule or Transverse Tubule that runs between terminal cisternae o Rapidly conduct nerve impulse to all sarcomeres brings extracellular materials to deeper parts of muscle fiber o 3 structures form a Triad 1 Terminal cisternae 2 T tubule 3 Terminal cisternae Muscle Contraction Generate a tension or pulling force within muscle Causes muscle to shorten Moves bone to which it is attached Conversion of chemical energy to mechanical energy mechanical work Contraction chemical process Movement mechanical process 7 Steps in muscle contractions 1 Stimulus a Nerve impulse arrives at muscle fiber to trigger contraction b Transmitted to sarcolemma now called a muscle action potential AP 2 Action Potential Spreads over surface of sarcolemma a Transmitted inward through t tubules to myofibrils 3 Ca release a AP travels along t tubules past terminal cisternae b Triggers opening of voltage regulated gates c Ca ions released from terminal cisternae 4 Ca catalyzes contraction process a In resting fiber Tropomyosin covers active site where myosin cross bridge attaches to actin b Ca bind to Troponin to change shape c Tugs on Tropomyosin to move it away from active site 5 Cross bridge attachment a Myosin cross bridges attracted to active site become physically attached to actin 6 Cross bridge pivots while attached to actin a Pulls actin myofilament toward center of sarcomere physically shortening sarcomere myofibril muscle fiber and whole muscle 7 Relaxation pump a Occurs when nerve fiber no longer provides stimulus b Ca ions pumped back into terminal cisternae uses active transport Ca c Cross bridges release from actin d Tropomyosin moves back to cover active site Sliding Filament Ratchet Theory Cross bridges attach and pull release reattach and pull etc Slide actin toward canter of sarcomere o Actin myosin do not change length o Actin is pulled past myosin o Sarcomere becomes shorter Single cross bridge pivot 1 shortening of muscle o Muscle shortens 35 50 of resting length Cross bridges attach reattach many times o Estimate half of available cross bridges pull at one time others are seeking new attachment sites If muscle is too stretched actin pulled beyond cross bridges contraction cannot occur As muscle shortens strength diminishes o Less tension or pulling force o No cross bridges in middle of myosin to pull actin o When actin is overlapped no cross bridges to pull it further Length tension relationship