Chapter 10: Structure and Function of Muscles PDF

Chapter 10: Structure and Function of Muscles Skeletal muscles Cardiac muscles Smooth muscles 1 Brief outlines only. For details, please refer to the Lecture Text on Top Hat ...

Chapter 10: Structure and Function of Muscles Skeletal muscles Cardiac muscles Smooth muscles 1 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  2 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Functional Characteristics Excitability or irritability and Conductivity Contractility Extensibility Elasticity 3 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Functions: Produce physical movements Maintain posture Joint stabilization Heat generation 4 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Skeletal Muscle Anatomy Muscles contain nerves, blood vessels, connective tissue. Origin and Insertion of Muscles for skeletal movements Origin - normally on immovable bone Insertion - normally on movable bone Muscle attachments: Direct or Indirect Direct attachment of epimysium fused to periosteum of bone or perichondrium cartilage Indirect attachment via tendon or aponeurosis Attachment to fascia of other muscles via fibrous raphe (linea alba) 5 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Skeletal Muscle Fiber Structure Muscle fiber is a single cell Unbranched, cylindrical, multinucleate, contain mitochondria Cell or plasma membrane called sarcolemma Endomysium: areolar connective tissue Perimysium: fibrous tissue Epimysium: dense fibrous connective tissue Deep fascia: fibrous connective tissue, forms tendons, ligaments etc. Superficial fascia (hypodermis) All connective tissue layers continuous with each other 6 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  7 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  8 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Structure of Sarcomere Each muscle fiber made of 100s of cylindrical myofibrils Each myofibril made of myofilaments Thin myofilaments – actin, anchored to Z-discs Thick myofilaments – myosin, arranged tail-to-tail Myofibrils made of sarcomeres I-band A-band Z-disc H-zone M-line 9 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  10 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Muscle Proteins Tropomyosin Covers the myosin binding sites on actin filaments Troponin TnT binds to tropomyosin forming troponin-tropomyosin complex TnC binds calcium ions TnI binds to actin filament to keep actin-tropomyosin complex in place blocking myosin binding sites 11 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Muscle Proteins Titin Elastic, Heavy molecular weight protein Runs through thick filaments Actinin Non-elastic, binds actin filaments to Z-disc Cross links thin filaments in adjacent sarcomeres for linear contraction Dystrophin Connects muscle cytoskeletal elements to extracellular matrix Duchenne Muscular Dystrophy Myosin binding protein C In heart, acts as a tether to limit number of cross bridges 12 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  13 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Actin filaments: * thin filaments * monomers polymeriz to form two twisted strands of F-actin * each filament has about 300-400 actin molecules * Actinin binds actin filaments to Z-line Tropomyosin * associated with actin filaments * fill the groove between the F-actin strands making it stiff Troponin * associated with tropomyosin * TnI, TnT, TnC 14 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Neuromuscular Junction Myoneural junction Axon of motor neuron connects to a muscle fiber Axons branch into axonal terminals One neuromuscular junction (one axonal terminal) per muscle fiber Motor Unit One motor neuron and all the muscle fibers it supplies Motor unit may be small or large Small motor units in eye muscles and muscles of hand for fine control Large motor units in leg muscles, no fine control needed 15 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  16 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Synaptic Transmission at Neuromuscular Junction Action potential from motor neurons in brain or spinal cord Activation of voltage-gated calcium channels Release of neurotransmitter (acetylcholine = Ach) Neurotransmitter (Ach) binds to Ach receptor on sarcolemma Sodium ions to enter muscle fiber Action potential generated in muscle fiber Release of calcium via voltage-gated calcium Calcium ions bind to troponin C Energized myosin heads extend to make cross bridges Ach degraded by acetylcholinesterase 17 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  18 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  19 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Skeletal Muscle Physiology: Sliding filament theory Excitation-Contraction Coupling 1. Stimulus (action potential) arrives at neuromuscular junction 2. Action potential spreads along the sarcolemma and T-tubules 3. Calcium ions released from SR 4. Energy in the form of ATP is used to make myosin-actin cross bridges Sliding continues as long as the Ca2+ and ATP are present Sarcomeres shorten, I-band and H-zone become smaller due to overlap Endomysium, perimysium and epimysium pull the bone via tendons 20 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Muscle relaxes back to resting state due to: No further stimulus arrives at motor end plate Ca2+ returned to SR by ATP-dependent Ca pump until used again Ach is degraded by Ach-esterase Myosin heads stop hydrolyzing ATP Rigor mortis Occurs 6 - 24 hours after death Due to lack of ATP Calcium ions are not pumped back to SR, 24-36 hours after death, muscles become flaccid Release of hydrolytic enzymes from lysosomes (autolysis) 21 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  22 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  23 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Energy Demands of Muscles Short Term Activity ATP present in muscles used for 10 seconds of activity Myokinase Creatine phosphate Glycolysis For 10-40 seconds of muscular activity Anaerobic oxidation of glucose yields 2 ATPs and 2 NADH2 Muscle glycogen, Lactic acid accumulation causes muscle fatigue Oxygen debt Krebs cycle Generates large amount of ATP by complete aerobic oxidation of glucose Useful during extended work Constant supply of oxygen is needed 24 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Types of Muscle Fibers (i) Slow Oxidative Fibers (Type I) Red, Myoglobin, Thin aerobic fibers Less force, Non-fatigable, Slow acting ATPase in myosin head Postural muscles (ii) Fast Oxidative Fibers (Type IIa) Pink, some Myoglobin, Thicker fibers Generate medium force, Less fatigable, Fast acting ATPase in myosin head, Muscles used in light work, walking (iii) Fast Glycolytic Fibers (Type IIb): White, no myoglobin, Thick glycolytic fibers Lot of force, Fatigable, Fast acting ATPase in myosin head, Muscles used, in weightlifting, sprint etc. 25 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Graded Muscle Contractions All-or-none phenomenon Contractions can be graded – Generate More or Less Force Muscle twitch: response to a threshold stimulus Latent phase Contraction phase Relaxation phase Summation occurs whenrate of stimulation increases and twitches fuse. Tetanus occurs when smooth continuous contractions are seen. Fatigue occurs when stimulation continues for an extended period of time and muscle loses its ability to maintain a contraction 26 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  27 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Isotonic muscle contraction Length of the muscle changes but the tension (force) remains constant. Isometric muscle contraction Length of the muscle remains constant but the tension (force) increases. Most muscle contractions are a combination of isotonic and isometric contractions. For example, lifting a book off the table would involve isotonic muscle contraction but to hold it up, without dropping, would be an isometric muscle contraction. Myasthenia gravis Autoimmune disease, Ach receptors, Muscle weakness Affects Extrinsic eye muscles, Muscles of eyelids and facial expression Muscles used in chewing, talking, and swallowing 28 Brief outlines only. For details, please refer to the Lecture Text on Top Hat Smooth Muscles GI tract, blood vessels, urinary bladder, uterus, urethra, ureter etc. Individual nucleated cells Sarcomeres arranged in a random fashion, Contract in 3-dimension No SR, depend on extracellular calcium present in caveolae for contraction Dense bodies (like Z-discs) serve to anchor thin filaments No troponin Calmodulin binds calcium, Activates MLCK, Cross bridge formation Respond to oxytocin, epinephrine, acetylcholine Stay extended without becoming fatigued Types of smooth muscles: Single unit Multi-unit 29 Brief outlines only. For details, please refer to the Lecture Text on Top Hat  30 Brief outlines only. For details, please refer to the Lecture Text on Top Hat