Muscle Physiology

I. Introduction of the "Contraction Specialists" A. Diversity of Function in the Human Body B. Categorization of Muscle 1. Skeletal 2. Smooth 3. Cardiac II. Structure of Skeletal Muscle A. Organization of the Muscle from Organ to Protein B. The Sarcomere = The Basic Functional Unit 1. Z line 2. M line 3. I band 4. A band 5. Addition of Sarcomeres - Growth verses Hypertrophy (Exercise) C. Activities During Contraction 1. Length Changes of the Sacromere 2. Cross Bridge Formation III. Molecular Basis of Skeletal Muscle Contraction A. Structure of the "Contractile Proteins" 1. The Thin Filaments a. Actin - Primary Structural Protein b. Tropomyosin - Regulatory Protein c. Troponin - Regulatory Protein 2. The Thick Filament a. Myosin 1. Function of the Hinge, Head, and Tail Regions During the "Power Stroke" B. The Sliding Filament Theory IV. Excitation-Contraction Coupling and Relaxation A. The Physical Roles of Specialized Structures and Events 1. ACh Initiation of the Action Potential 2. Establishment of the EPP 3. Transverse Tubule (T Tubule) and the Voltage Sensor 4. Sarcoplasmic Reticulum (SR) and the Ryanodine Receptor 5. Final Ca2+ Release B. Relaxation 1. Role of Calsequestrin 2. Role of SR Ca Pumps C. Cross Bridge Cycling 1. Requires Ca, ATP/Mg, and the Action Potential 2. 4 Major Steps a. Energize Myosin b. Binding Actin to Myosin c. The Power Stoke d. Detachment V. Skeletal Muscle Mechanics A. Contraction of Whole Muscles 1. Strength of Contraction is Dependent Upon a. Number of Fibers Contracted 1. The Motor Unit and Recruitment b. Development of Muscle Tension 1. Frequency of Stimulation 2. Length of Muscle at Rest 3. Extent of Fatigue 4. Thickness of Fiber 2. A Closer Look at Tension and Stimulation Frequency 1. Twitch 2. Summation 3. Tetanus 4. Fatigue a. Cellular Fatigue b. Neuromuscular Fatigue c. Central Fatigue 5. Recovery VI. Muscle Atrophy and Disease A. Atrophy Can Occur Due to 1. Lack of Exercise 2. Immobility 3. Denervation 4. Age B. Muscle Disease - Muscular Dystrophy 1. Gene Therapy Approach 2. Cell-Transplant Approach VII. Smooth and Cardiac Muscle A. Unique Smooth Muscle Properties 1. Hollow Tubes and Organs 2. Spindle Shape Not Extended Muscle Length 3. 75% less Myosin Although Longer 4. No Troponin 5. A New "Contractile Fiber" - Intermediate Filament 6. No Myofibrils or "True" Sarcomeres 7. Dense Bodies Replace Z lines 8. 15 Actin : 1 Myosin (not 2:1) 9. Sliding Filament is a Lattice Arrangement 10. Contains Elastin and Collagen 11. Circumferential Function Around Vessels 12. No T-tulules 13. Source of Ca - Two Different Pools a. SR (Sarcoplasmic Reticulum) b. ECF (Extracellular Fluid) 14. Release of Ca from SR is Not Due to Voltage... a. Use of Inositol Trisphosphate (IP3) Second Messenger 15. Excitation-Contraction Coupling Via Myosin Phosphorylation... a. the Ca-Calmodulin Complex b. Activation of Myosin Kinase 16. Four Major Locations for ATP Utilization 17. The Latch Phenomenon - Why Smooth Muscle IS EXTREMELY ECONOMICAL BUT SLOW! VIII. Self-Generated Electrical Activity in Smooth Muscle A. Two Categories of Smooth Muscle Electrical Excitation 1. Multi-unit Smooth a. Neurogenic b. Independent Contraction 2. Single-unit Smooth a. Myogenic b. Use of Gap Junctions c. The Functional Syncytium d. Two Major Types of Spontaneous Depolarizations 1. Pacemaker Activity 2. Slow Wave Potential IX. Unique Cardiac Muscle Properties 1. Striation 2. Actin/Myosin Arranged like Skeletal Muscle 3. Has Troponin and T-Tubules 4. Ca Regulated Troponin NO Myosin Phosphorylation 5. Has Two Pools of Ca 6. Myogenic NOT neurogenic 7. Gap Junctions 8. Modulated By Drugs and Hormones