Unit 5.2 The Muscular System PDF

PRAYER BEFORE CLASS Holy Spirit, Divine Creator, true source of light and fountain of wisdom! Pour forth your brilliance upon my dense intellect, dissipate the darkness which covers me, that of sin and of ignorance. Grant me a penetrating mind to understand, a retentive memory, method and ease of le...

PRAYER BEFORE CLASS Holy Spirit, Divine Creator, true source of light and fountain of wisdom! Pour forth your brilliance upon my dense intellect, dissipate the darkness which covers me, that of sin and of ignorance. Grant me a penetrating mind to understand, a retentive memory, method and ease of learning, the lucidity to comprehend, and abundant grace in expressing myself. Guide the beginning of my work, direct its progress and bring it to successful completion. This I ask through Jesus Christ, true God, and true man, living and reigning with You and the Father, forever and ever. Amen. ANATOMY AND PHYSIOLOGY WITH PATHOPHYSIOLOGY THE MUSCULAR SYSTEM Learning Outcome Describe the general functions of the muscular system and integrate an understanding of its physiology with the pathophysiology of common diseases and conditions affecting this system. Outline Introduction Muscular System Physiology Diseases of the Muscular System Diagnostic Tests of the Muscular System II. PHYSIOLOGY THE MUSCULAR SYSTEM Neuromuscular Junction Structure NEUROMUSCULAR JUNCTION: - Stimulation of muscle cell by a nerve happens at a neuromuscular junction Neuromuscular Junction Structure NEUROMUSCULAR JUNCTION is FORMED from: AXONAL ENDINGS ○ Have small membranous sacs (synaptic vesicles) containing acetylcholine MOTOR END PLATE ○ Muscle plasma membrane in the area of the junction ○ Contains acetylcholine receptors Neuromuscular Junction Structure Though exceedingly close, axonals ends and muscle fibers are always separated by a space called the synaptic cleft Neuromuscular Junction Structure Physiology of Muscular System: MUSCLE CONTRACTION STEPS OF MUSCLE CONTRACTION AT NMJ: 1. ACTION POTENTIAL ARRIVES AT THE PRESYNAPTIC TERMINAL - Voltage gated calcium channels in the presynaptic membrane open Physiology of Muscular System: MUSCLE CONTRACTION STEPS OF MUSCLE CONTRACTION AT NMJ: 2. INITIATION OF THE RELEASE OF ACETYLCHOLINE FROM SYNAPTIC VESICLES Physiology of Muscular System: MUSCLE CONTRACTION STEPS OF MUSCLE CONTRACTION AT NMJ: 3. ACETYLCHOLINE IS RELEASED INTO THE SYNAPTIC CLEFT BY EXOCYTOSIS Physiology of Muscular System: MUSCLE CONTRACTION STEPS OF MUSCLE CONTRACTION AT NMJ: 4. ACETYLCHOLINE BINDS TO LIGAND-GATED SODIUM CHANNELS ON THE MOTOR END PLATE Physiology of Muscular System: MUSCLE CONTRACTION STEPS OF MUSCLE CONTRACTION AT NMJ: 5. LIGAND GATED SODIUM CHANNELS OPEN AND SODIUM ENTERS THE MUSCLE FIBER - Action potential is generated if depolarization passes threshold Physiology of Muscular System: MUSCLE CONTRACTION STEPS OF MUSCLE CONTRACTION AT NMJ: 6. ACETYLCHOLINE UNBINDS FROM THE LIGAND GATED CHANNELS, WHICH THEN CLOSE Physiology of Muscular System: MUSCLE CONTRACTION STEPS OF MUSCLE CONTRACTION AT NMJ: 7. ACETYLCHOLINESTERASE REMOVES ACETYLCHOLINE FROM THE SYNAPTIC CLEFT Physiology of Muscular System: MUSCLE CONTRACTION STEPS OF MUSCLE CONTRACTION AT NMJ: 8. CHOLINE IS SYMPORTED WITH SODIUM IN THE PRESYNAPTIC TERMINAL Physiology of Muscular System: MUSCLE CONTRACTION STEPS OF MUSCLE CONTRACTION AT NMJ: 9. ACETYLCHOLINE IS REFORMED WITHIN THE PRESYNAPTIC TERMINAL  Actin and Myosin Myofilament Structure ACTIN MYOFILAMENT COMPONENT - Globular (G) actin - Globular subunits that forms a strand called fibrous (F) actin - Tropomyosin - In relaxed muscle, covers the active sites on the G actin subunits. - Troponin - Anchors the troponin to the actin - Prevents the tropomyosin from uncovering the G actin active sites in a relaxed muscle - Binds calcium  Actin and Myosin Myofilament Structure ACTIN MYOFILAMENT COMPONENT - Globular (G) actin - Globular subunits that forms a strand called fibrous (F) actin - Tropomyosin - In relaxed muscle, covers the active sites on the G actin subunits. - Troponin - Anchors the troponin to the actin - Prevents the tropomyosin from uncovering the G actin active sites in a relaxed muscle - Binds calcium  Actin and Myosin Myofilament Structure MYOSIN MYOFILAMENT COMPONENT - Myosin molecules - Two myosin heavy chains - Two myosin heads - Bind to active sites on actin molecules to form cross bridges - Attached to the rod portion by a hinge region - Heads are ATPase enzymes Physiology of Muscular System: EXCITATION-CONTRACTION COUPLING Excitation-contraction coupling occur at the triad ○ Link between electrical component of muscle contraction to the mechanical component In order to contract, a skeletal muscle must: ○ Be stimulated by a nerve ending ○ Propagate an action potential along its sarcolemma ○ Have a rise in intracellular calcium levels, the final trigger contraction Physiology of Muscular System: EXCITATION-CONTRACTION COUPLING Physiology of Muscular System: EXCITATION-CONTRACTION COUPLING Physiology of Muscular System: CROSS-BRIDGE MOVEMENT Physiology of Muscular System: CROSS-BRIDGE MOVEMENT Physiology of Muscular System: CROSS-BRIDGE MOVEMENT MUSCLE RELAXATION OCCURS: 1. Acetylcholine is no longer released at the neuromuscular junction 2. Cessation of action potential along the sarcolemma stops calcium release 3. Calcium diffuses away from the troponin molecules 4. Tropomyosin covers the G actin active sites 5. No formation of cross bridges Physiology of Muscular System: TYPES OF MUSCLE CONTRACTIONS ISOMETRIC CONTRACTIONS - Muscle does not shorten - Tension increases ISOTONIC CONTRACTIONS - Muscle shortens - Tone remains constant throughout the contraction - Two types: concentric and eccentric contractions III. DISORDERS AND DIAGNOSTIC TESTS THE MUSCULAR SYSTEM DISORDERS OF MUSCULAR SYSTEM AGING - Muscle atrophy - Physiologic - Age related reduction in muscle mass and regulation of muscle function - Loss of muscle fibers begins as early as 25 years old - Surface area of the NMJ and number of motor neurons decreases DISORDERS OF MUSCULAR SYSTEM MUSCLE FATIGUE - Physiologic condition - Temporary state of reduced work capacity - Mechanisms involved - Acidosis and ATP depletion - Oxidative stress - Local inflammatory response DISORDERS OF MUSCULAR SYSTEM MUSCLE SORENESS - Occurs after vigorous exercise - Causes - Inflammatory chemical influx into the muscle fibers DISORDERS OF MUSCULAR SYSTEM CRAMPS - Painful - Spastic contractions of skeletal muscle - Causes - Dehydration - Ion imbalance DISORDERS OF MUSCULAR SYSTEM TENDINITIS - Inflammation of a tendon or its attachment point due to overuse of a skeletal muscle FIBROMYALGIA - Non-life-threatening chronic widespread pain in skeletal muscles with no known cure - Chronic muscle pain syndrome DISORDERS OF MUSCULAR SYSTEM MYASTHENIA GRAVIS - Autoimmune disease - Production of autoantibodies that bind to acetylcholine receptors Diagnostics: Electromyography Identification of autoantibodies DISORDERS OF MUSCULAR SYSTEM DUCHENNE MUSCULAR DYSTROPHY - Mutations in the dystrophin gene on the x chromosome - Progressive muscle weakness and muscle contractures - Slow motor development with progressive weakness and muscle wasting - Muscular weakness begins in the hip muscles (waddling gait) - Rising from the floor using the hands and arms DISORDERS OF MUSCULAR SYSTEM DUCHENNE MUSCULAR DYSTROPHY Diagnostics: Serum creatinine Muscle biopsies Immunohistochemical studies ANATOMY AND PHYSIOLOGY WITH PATHOPHYSIOLOGY THE MUSCULAR SYSTEM Formative Assessment 1. Which of the following is not a major property of muscle? a. Contractility b. Elasticity c. Excitability d. Extensibility e. Secretability Formative Assessment 1. Which of the following is not a major property of muscle? a. Contractility b. Elasticity c. Excitability d. Extensibility e. Secretability Formative Assessment 2. Which of these statements about the molecular structure of myofilaments is true? a. Tropomyosin has a binding site for calcium b. The head of myosin molecule binds to an active site on G actin c. ATPase is found on troponin d. Actin molecules have a hinglike portion, which bends and straightens during contraction Formative Assessment 2. Which of these statements about the molecular structure of myofilaments is true? a. Tropomyosin has a binding site for calcium b. The head of myosin molecule binds to an active site on G actin c. ATPase is found on troponin d. Actin molecules have a hinglike portion, which bends and straightens during contraction Formative Assessment 3. Part of the sarcolemma that invaginates into the interior of skeletal muscle fibers is the a. T tubule b. Sarcoplasmic reticulum c. Synaptic vesicles d. Mitochondria Formative Assessment 3. Part of the sarcolemma that invaginates into the interior of skeletal muscle fibers is the a. T tubule b. Sarcoplasmic reticulum c. Synaptic vesicles d. Mitochondria Formative Assessment 4. A weight lifter attempts to lift a weight from the floor, but the weight is so heavy that he is unable to move it. The type of muscle contraction the weight lifter is using is mostly a. Isotonic contraction b. Isometric contraction c. Hypotonic contraction d. Hypertonic contraction Formative Assessment 4. A weight lifter attempts to lift a weight from the floor, but the weight is so heavy that he is unable to move it. The type of muscle contraction the weight lifter is using is mostly a. Isotonic contraction b. Isometric contraction c. Hypotonic contraction d. Hypertonic contraction Formative Assessment 5. Given these events: (1) Calcium ions combine with tropomyosin. (2) Calcium ions combine with troponin. (3) Tropomyosin pulls away from actin. (4) Troponin pulls away from actin. (5) Tropomyosin pulls away from myosin. (6) Troponin pulls away from myosin. (7) Myosin binds to actin. Choose the arrangement that lists the events in the order they occur during muscle contraction. a. 1,4,7 b. 1,3,7 c. 2,3,7 d. 2,4,7 Formative Assessment 5. Given these events: (1) Calcium ions combine with tropomyosin. (2) Calcium ions combine with troponin. (3) Tropomyosin pulls away from actin. (4) Troponin pulls away from actin. (5) Tropomyosin pulls away from myosin. (6) Troponin pulls away from myosin. (7) Myosin binds to actin. Choose the arrangement that lists the events in the order they occur during muscle contraction. a. 1,4,7 b. 1,3,7 c. 2,3,7 d. 2,4,7 References VanPutte, C. L., & Seeley, R. R. (2020). Seeley's anatomy & physiology. (12th ed.). New York, NY: McGraw-Hill Abbas, A. K., & Aster, J. C. (2021). Robbins & Cotran pathologic basis of disease (V. Kumar, Ed.; Tenth edition). Elsevier.