Skeletal Muscles

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 Myofilaments Myofibrils made up of 1000s of thin and thick myofilaments

Thin filaments Actin Tropomyosin Troponin Thick filaments

myosin 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 into the sarcoplasm binds with troponin on thin myofilaments (distracts chaperones) Tropomyosin shift to expose actins active site

Energized myosin heads bind with actins active site and pulls 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 actins 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 actins active sites contraction of myofilaments Lack of ATP after death causes cross bridges to stick

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

Oxygen & Glucose O2 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 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 resynthesize 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 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

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 Isometric tension changes; length of the muscle remains the same

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