48_lol_muscle.docx Bio 48 - Human Physiology Biology 48 - Human Physiology Lecture Summary Sheet - Norris Muscle Physiology I. Three types of muscle tissue A. Skeletal (striated, voluntary) B. Visceral or Smooth (nonstriated, involuntary) C. Cardiac (striated, involuntary) II. Basic Functions of Muscle A. Movement (primary) B. Maintain Posture C. Heat Generation III. General Characteristics of Muscle A. Excitability B. Contractility C. Extensibility D. Elasticity IV. Microscopic Structure / Anatomy (Skeletal Muscle) A. Sarcolemma (plasma membrane) 1. Transverse tubules (T-tubules) B. Sarcoplasm (cytoplasm) C. Specialized organelles: 1. Sarcoplasmic Reticulum (smooth endoplasmic reticulum) 2. Myofibrils a. Sarcomere i. I band ii. A band 3. Myofilaments (cytoskeleton) a. thick filaments (myosin) b. thin filaments (actin, tropomyosin and troponin) V. Physiology of Skeletal Muscle Contraction A. Sliding Filament Theory 1. Actin-Myosin Interaction a. actin-myosin binding b. power stroke / release of ADP + Pi c. ATP binding / unbinding of actin-myosin d. ATP hydrolysis / cocking of myosin head B. Activation of Muscular Contraction 1. Anatomy of the Synapse – the “neuromuscular junction” a. neuron terminal b. synaptic cleft c. motor end plate 2. motor units48_lol_muscle.docx Bio 48 - Human Physiology 3. Sequence (Excitation-Contraction Coupling): a. AP arrives at neuron terminal (at neuromuscular junction), Ca2+ rushes into terminal b. Vesicles release ACh into synaptic cleft, ACh diffusesacross synaptic cleft c. ACh binds to receptors on motor end plate (ACh destroyed by acetylcholinesterase) d. Chemically gated Na+ channels open in response to ACh binding – Na+ enters and produces a depolarizing graded potential (EPP) e. Graded potential triggers voltage gated channels producing an action potential f. AP propagates along membrane and down T-tubules opening Ca2+ channels in SR g. Sarcoplasmic reticulum releases calcium ions into sarcoplasm h. Calcium binds to troponin, troponin-tropomyosin moves exposing binding sites on actin i. Myosin heads bind to sites on actin and pull (power stroke) j. Relaxation occurs when Ca2+ is removed (actively pumped back into SR) VI. Muscle Responses A. Twitch Components 1. Latent Period 2. Contractile Interval 3. Relaxation Interval B. Single Cell Contractile Properties 1. All-or-None 2. Temporal Summation (“piggyback”) 3. Length-Tension Relationship C. Whole Muscle Contractile Properties 1. Spatial Summation ("recruitment") 2. Temporal (asynchronous contraction) 3. Elastic Components 4. Muscle Tone VII. Endurance A. Blood Supply B. Fiber Type 1. slow twitch (type I) - aerobic 2. fast twitch (type II) - anaerobic C. Fatigue D. Oxygen Debt VIII. Neural Control A. Sensory Receptors 1. Golgi Tendon Organs48_lol_muscle.docx Bio 48 - Human Physiology 2. Muscle Spindles a. Extrafusal Fibers b. Intrafusal Fibers c. Sensory Endings B. Skeletal Muscle Innervation 1. Lower Motor Neurons - "final common pathway" a. Alpha Motor Neurons - extrafusal fibers b. Gamma Motor Neurons - intrafusal IX. Smooth Muscle A. Structure / Anatomy 1. Filament Arrangement 2. Gap Junctions B. Mechanism of Activation 1. Calcium Channels 2. Indirect Activation of Myosin C. Types of Smooth Muscle 1. Single Unit 2. Multiple Unit D. Special Features 1. Active Range (can contract over a long range of stretch) 2. Myogenic Contraction (intrinsically contracts in response to stretch) 3. Activated by Ca2+ influx (may be associated with AP or GP) X. Cardiac Muscle - to be covered in detail at a later time A. Structure / Anatomy B. Functional Syncytium XI. Additional Key Terms (FYI) aerobic anaerobic ATP atrophy creatine phosphate extrafusal hypertrophy in vitro in vivo intrafusal isometric isotonic recruitment tetanus48_lol_muscle.docx Bio 48 - Human Physiology Study Questions – Muscle Physiology: 1. Compare and contrast Skeletal, Visceral and Cardiac muscle. Discuss each in terms of location, histology, control and general structure. 2. Describe the basic functions of muscle. 3. Identify and describe the four general characteristics of muscle. 4. Name and describe the different components (aka organelles) of a skeletal muscle cell. Describe the function of each, and their structural and functional relationship to each other. 5. Describe the structure of the myofibril. Identify the different bands and explain them with reference to the arrangement of the thin and thick filaments. 6. Describe the structural and functional relationship between the bands in the myofibril and the T-tubule. 7. Describe the molecular structure of the thin and thick filaments. Explain the significance of the different molecular components. 8. Myosin exhibits three different properties necessary to its role in contraction, what are they? 9. What is the functional significance of the troponin-tropomyosin complex? 10. Describe the evidence supporting the sliding filament theory (as opposed to filament shortening). 11. Describe the sequence of events of the sliding filament phase of contraction (see fig 1). When is calcium needed? At which two points is ATP required? 12. Describe the structure of a generic chemical synapse. Compare and contrast the neuromuscular junction with this generic synapse. 13. What is a motor unit? 14. Explain in detail ALL of the events leading up to contraction beginning at the time the nerve impulse (action potential) arrives at the neuron terminal of the neuromuscular junction. 15. What is a muscle twitch? 16. Define and describe what is occurring during the latent, contraction and relaxation intervals of a muscle twitch. 17. What does “all-or-none” mean? 18. Define “temporal summation”. Describe temporal summation as it applies to a single muscle cell. 19. Describe and explain how the initial length of the muscle cell (or sarcomere) influences the contractile strength of the muscle cell. 20. Define “spatial summation”. Describe spatial summation as it applies to a muscle. 21. Describe the pattern of motor unit recruitment as muscle contraction strength increases. How does this influence the fine control of a muscle as contraction strength increases? 22. Explain how a muscle can contract continuously without any of the cells within the muscle contracting continuously. 23. Compare and contrast slow and fast twitch muscle fibers. 24. Define