Muscle Physiology Chapter 11

Connective Tissue Components Muscle cell = muscle fiber Endomysium – covers muscle fiber Perimysium – binds groups of muscle fibers (fasicles) Epimysium – covers the entire muscle Tendon – fibrous tissue that connects muscle to bone Aponeurosis – broad, flat sheet of connective tissue Fascia – fibrous CT surrounding muscle and tendon

Overview of Muscle Cell Muscle cell = muscle fiber Sarcolemma = plasma membrane Sarcoplasm = cytoplasm Sarcoplasmic reticulum (SR) = network of tubules and sacs Multi-nucleated, multiple mitochondrion Bundles of myofibrils extend lengthwise & fill sarcoplasm Composed of thick and thin myofilaments

Sarcomere Contractile unit of a muscle fiber each myofibril consists of many sarcomeres Z line Anchors thin filaments Boundary of sarcomere M line – anchors thick filaments A band: segment of thick & thin filaments I band: segment of thin filaments H zone: where thin and thick filaments will not overlap (only thick)

Sarcomere cont… Elastic filaments – connect thick filaments to Z line T (transverse) tubules – allows impulses traveling along sarcolemma to move deeper within the cell Triad – t tubule sandwiched between sacs of the SR Allows impulses traveling along a t tubule to stimulate sacs of the SR

Myofilaments Myofibrils – made up of 1000s of thin and thick myofilaments Thin filaments Actin Tropomyosin Troponin Thick filaments myosin

Actin molecules strung together like beads to form two fibrous strands that twist around each other Actin and myosin molecules have a chemical attraction to each other At rest – actin active sites are covered by tropomyosin; tropomyosin held in place by troponin Myosin filaments – heads stick out from bundles; attracted to actin

Muscle Excitation Nerve impulse reaches the end of a motor neuron  releases acetylcholine (Ach) Ach diffuses across the neuromuscular junction and binds with the receptors on the motor endplate

Muscle Contraction Impulses travel along the sarcolemma  t tubules  sacs of SR Ca2+ is released (balloons to distract)into the sarcoplasm  binds with troponin(chaperone) Tropomyosin shift to expose actin’s active site Energized myosin (Boy) KISSES (bind) with actin’s(girl) active site and pulls (her to middle of the dance floor)thin filament towards center of sarcomere Requires ATP

Muscle Relaxation Nerve impulse is complete  Ca2+ is pumped back into the sacs of the SR Ca2+ is stripped from the troponin  tropomyosin covers the actin’s active site Myosin heads can no longer bind with actin  muscle fiber returns to its resting length

http://www.sci.sdsu.edu/movies/actin_myosin_gif.html

Rigor Mortis “stiffness of death” SR releases excess Ca2+  myosin heads bind with actin’s active sites  contraction of myofilaments Lack of ATP after death causes cross bridges to “stick”

http://highered. mcgraw-hill http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter9/

Alternate Source of Energy ATP must be continually re-synthesized Breakdown of creatine-phosphate (CP) provides energy for ATP re-synthesis Catabolism of food provides energy for ATP and CP synthesis

Aerobic vs. Anaerobic Respiration Oxygen-requiring process Produces maximum amount of ATP from one glucose molecule Anaerobic Respiration Does not require oxygen Short-term, rapid process to re-synthesize ATP Produces lactic acid Burning/soreness in muscles

Heat Production Some energy from catabolic processes is lost as heat Muscle release massive amts of heat Thermoreceptors sense decrease in body temp  hypothalamus integrates information  signal sent to skeletal muscle to contract  shivering  homeostatic balance is maintained

http://natchem.files.wordpress.com/2009/11/motor-unit-lg.jpg

Isotonic vs Isometric Contractions Isotonic – tension remains the same; length of the muscle changes Concentric contraction: muscle shortens (contracts) Eccentric contraction : muscle lengthens Isometric – tension changes; length of the muscle remains the same Myosin heads unable to move thin filaments Static tension