Muscle Physiology 2 Pre-Lecture Notes PDF

Applied Sciences PT4050 and PT7001 Muscle Physiology Part 2 Chris Chamberlin and Dr Ben Hunter [email protected] Learning Outcomes Smooth muscle Structure and innervation Three muscle types Skeletal, smooth, cardiac Contraction regulation i...

Applied Sciences PT4050 and PT7001 Muscle Physiology Part 2 Chris Chamberlin and Dr Ben Hunter [email protected] Learning Outcomes Smooth muscle Structure and innervation Three muscle types Skeletal, smooth, cardiac Contraction regulation in smooth and skeletal muscle Energy supply Types of Muscle Types of Muscle Skeletal Muscle · Striation (sarcomeres) · Effector of somatic nerve system · Voluntary contraction · Neuromuscular junction-specific · Multi-nuclei (fusion) Smooth Muscle · No striation (filaments not form sarcomeres) · Effector of autonomic nerve system · Involuntary contraction · Varicosites-diffuse · Gap junctions Cardiac Muscle · Striation (sarcomeres) · Effector of autonomic nerve system · Involuntary contraction · Gap junctions · Intercalated disks ”On-off switch” – Skeletal and Cardiac · Interaction of actin and myosin depends on regulatory proteins on the thin filament: · Tropomyosin – blocks myosin binding sides on actin · Troponin C – binding site for Ca2+ · Troponin T – binds to tropomyosin · Troponin I – binds to actin · Ca2+ binds to troponin-C then a conformational change occurs which moves tropomyosin · This then revelas the myosin binding site and a cross-bridge can form ”On-off switch” – Smooth · Smooth muscle doesn’t contain troponin, therefore Ca2+ triggers contraction via different mechanism · Ca2+ binds to protein called calmodulin · Binds to myosin light chain kinase (MLCK) · Myosin light chains are then phosphorylated · This permits the binding of myosin to actin Depolarisation in different muscle · Skeletal – AP triggers release of calcium from SR · Cardiac and smooth – the AP and source of calcium differ Twitch contraction Contraction produced in response to a single action potential All or nothing for a given muscle fibre Can be induced for a muscle fibre, a motor unit or a whole muscle Latency: time delay between stimulation (nerve AP or direct electrical) – E-C coupling Contraction phase – cross-bridge cycling Relaxation phase – Ca2+ uptake Twitch contraction Frequency and Summation Action potential: 2 ms Contraction: 10–200 ms, possible to summate Tension (force) depends on [Ca2+]i Freq. of stim., Ca2+ release>uptake, [Ca2+]i When the system is saturated (all troponin bind with Ca2+ and cross-bridge cycling maxed out) – tetanus (long lasting contraction) Frequency and Summation Energy Production - ATP Energy Production - ATP How does ATP provide energy? Reaction (catabolic) - ATP  ADP + P + Energy + Heat Stores of ATP in body are sufficient for few seconds of maximal work. Energy Production – PCr System PCr used as follows: PCr  P + Cr + Energy Facilitated by the enzyme creatine kinase Energy released from catabolic PCr reaction ADP + P + Energy  ATP Anabolic reaction – phosphate and energy reform ATP Energy Production – Glycolysis 10 enzyme-controlled reactions Glycolysis  breakdown of 6-carbon molecule - Glucose (C6H12O6)  two 3-carbon molecule of pyruvic acid (C3H6O3) Net gain of 2 ATP All reactions are reversible  Energy Production – Glycolysis “CHO” 10 Enzyme ATP Synthesised Controlled Reactions Pyruvate No oxygen Oxygen Lactic acid Krebs cycle Just to get this right…  Energy Production – Glycolysis “CHO” 10 Enzyme ATP Synthesised Controlled Reactions Pyruvate No oxygen Oxygen Lactic acid Krebs cycle Energy Production – Aerobic Pathways Energy Production – Aerobic Pathways Krebs cycle (or citric acid cycle) consists of a series of reactions that result in a net production of (per molecule of glucose): 2 x ATP ( = 2 ATP from glycolysis) = 4 ATP 6 x NADH (+ 4 NADH from glycolysis) = 10 NADHs ≈ 30 ATP 2 x FADH2 ≈ 4 ATP 38 ATPs produced from complete oxidation of glucose (Krebs and Electron Transport Chain)  Triglyceride Energy Production – Aerobic Pathways Glycerol Glycerol 3x Fatty acid Enters glycolysis Moved into Kreb’s cycle H+ taken to electron transfer chain Glycolysis Acetyl Co-A Total energy production 15-19 ATP Krebs cycle Krebs cycle Fatty acids H+ ions H+ ions When not attached to glycerol called free fatty acids Broken down by beta-oxidation ETC ETC Acetyl coenzyme A is taken to Kreb's cycle H+ taken to electron transfer chain Each Fatty acid, 129 ATP 129 (x3) = 19 ATP 387 ATP Energy Production – Systems Summary See learning outcomes.