1. Muscle Physiology Chapter 11

2. 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

4. 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

6. Sarcomere Contractile unit of a muscle fiber each myofibril consists of many sarcomeres

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

12. 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

13. Muscle Contraction Impulses travel along the sarcolemma  t tubules  sacs of SR Ca 2+ is released into the sarcoplasm  binds with troponin on thin myofilaments (distracts chaperones) Tropomyosin shift to expose actin’s active site Energized myosin heads bind with actin’s active site and pulls thin filament towards center of sarcomere –Requires ATP

16. Muscle Relaxation Nerve impulse is complete  Ca 2+ is pumped back into the sacs of the SR Ca 2+ 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

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

18. Rigor Mortis “stiffness of death” SR releases excess Ca 2+  myosin heads bind with actin’s active sites  contraction of myofilaments Lack of ATP after death causes cross bridges to “stick”

19. Energy for Contractions Hydrolysis (breakdown) of ATP –ATP  ADP –ATP binds to return myosin head back to resting position

20. Oxygen & Glucose O 2 and glucose are the starting materials for cellular respiration During rest oxygen is stored in myoglobin – High amounts of myoglobin = red fibers = slow twitch fibers – Low levels of myoglobin = white fibers = fast twitch fibers

21. Aerobic vs. Anaerobic Respiration Aerobic 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

22. 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

23. Motor Unit Motor unit = motor neuron + muscle fibers it attaches to Motor neurons can innervate few to 100s of muscle fibers A lower number of muscle fibers within a motor unit = more precise movement –Ex: hand vs abdomen

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

25. Isotonic vs Isometric Contractions Isotonic – tension remains the same; length of the muscle changes Isometric – tension changes; length of the muscle remains the same