L17 NPB 101 - Lecture 17 •  SmartSite: – ...

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Unformatted text preview: Lecture 17 •  SmartSite: –  Lecture 17 Notes –  Midterm 1 (Wed 10/20): •  •  •  •  •  Reading (Recommended): •  Announcements: –  Relevant por?ons of Chapters 7 & 8 30 MC ques?ons Covers lectures through Monday Star?ng Tuesday, lectures on Midterm 2) Requires students to bring and use SCANTRON 2000 (blue) •  Review •  Muscle –  Skeletal muscle –  Skeletal muscle –  Exam Room (based on Last Name) –  CAF Office Hrs (197 Briggs) •  T 9 ­10 and 5 ­6 •  A ­D in 1322 Storer •  E ­Z in 123 Sci Lec Hall (regular room) –  EL Office Hrs (2041A SLB) •  M 5 ­7 •  Tu/Th 1 ­3 (Regular) 1 REV: Muscle •  Muscle as a ?ssue – similari?es, differences & func?on •  Skeletal muscle morphology – muscle to myofiber to myofibril to sarcomere •  Four proteins – myosin, ac?n, tropomyosin, troponin •  Contrac?on – sliding filament mechanism 2 REV: Cross Bridge (Power Stroke) •  Ac?vated cross bridge bends toward center of thick filament, “rowing” in thin filament to which it is adached •  Ca2+ released into sarcoplasm (cytoplasm of muscle cell) •  Myosin heads bind to ac?n •  Myosin heads swivel toward center of sarcomere (power stroke) •  ATP binds to myosin head and detaches it from ac?n •  Hydrolysis of ATP transfers energy to myosin head and reorients it •  Contrac?on con?nues if ATP is available and Ca2+ level in sarcoplasm is high 3 Cross ­Bridge Cycle 4 Fig. 8 ­12; pg. 267 Excita?on ­Contrac?on Coupling 5 The Neuromuscular Junction Fig. 7 ­4; pg. 249; Fig. 7 ­5a; pg. 250 6 Transverse Tubules •  T ­tubules •  Run perpendicularly from surface of muscle cell membrane into central por?ons of the muscle fiber •  Since membrane is con?nuous with surface membrane – ac?on poten?al on surface membrane also spreads down into T ­tubule •  Spread of ac?on poten?al down a T ­tubule triggers release of Ca2+ from sarcoplasmic re?culum into cytosol Fig. 8 ­9; pg. 264 7 Sarcoplasmic Re?culum •  Modified endoplasmic re?culum •  Consists of fine network of interconnected compartments that surround each myofibril •  Not con?nuous but encircles myofibril throughout its length •  Segments are wrapped around each A band and each I band –  Ends of segments expand to form saclike regions – lateral sacs (terminal cisternae) Fig. 8 ­9; pg. 264 8 Rela?onship Between T ­Tubule and Sarcoplasmic Re?culum Fig. 8 ­10; pg. 265 9 Ca2+ in Excita?on ­Contrac?on Coupling Fig. 8 ­11; pg. 266 10 Relaxa?on •  Reuptake of Ca2+ into sarcoplasmic re?culum (SR) –  Ac?ve transport with Ca2+ pump. •  Acetylcholinesterase breaks down ACh at neuromuscular junc?on •  Muscle fiber ac?on poten?al stops •  When local ac?on poten?al is no longer present, Ca2+ moves back into SR 11 The Mechanics of Muscle Contrac?on 12 Speed of Contrac?on is Related To the Load on the Muscle Fig. 8 ­20; pg. 274 13 Length ­Tension Rela?onship •  Maximum tension is generated at the op?mal length (L0) Fig. 8 ­19; pg. 273 14 Length ­Tension Rela?onship •  Less than op?mal length –  Bunching thick filaments –  Thin filament overlap –  Ca2+ influx reduced •  Too Stretched –  Less than op?mal overlap Fig. 8 ­19; pg. 273 15 Muscle Contrac?ons •  Contrac?ons of whole muscle can be of varying strength •  Twitch –  Brief, weak contrac?on –  Produced from single ac?on poten?al –  Too short and too weak to be useful –  Normally does not take place in body •  Two primary factors which can be adjusted to accomplish grada?on of whole ­muscle tension –  Number of muscle fibers contrac?ng within a muscle –  Tension developed by each contrac?ng fiber 16 The Motor Unit •  Motor unit –  One motor neuron and the muscle fibers it innervates •  Number of muscle fibers varies among different motor units •  Number of muscle fibers per motor unit and number of motor units per muscle vary widely –  Muscles that produce precise, delicate movements contain fewer fibers per motor unit –  Muscles performing powerful, coarsely controlled movement have larger number of fibers per motor unit Fig. 8 ­16; pg. 270 17 Contrac?on Strength of Small Versus Large Motor Units Fig. 8 ­17; pg. 270 18 Motor Unit Recruitment •  Asynchronous recruitment of motor units helps delay or prevent fa?gue •  Factors influencing extent to which tension can be developed –  Frequency of s?mula?on –  Length of fiber at onset of contrac?on –  Extent of fa?gue –  Thickness of fiber 19 Twitch Summa?on and Tetanus •  Twitch summa?on –  Results from sustained eleva?on of cytosolic calcium •  Tetanus –  Occurs if muscle fiber is s?mulated so rapidly that it does not have a chance to relax between s?muli –  Contrac?on is usually three to four ?mes stronger than a single twitch 20 Summa?on and Tetanus Fig. 8 ­18; pg. 271 21 Major Types of Skeletal Muscle Fibers •  Classified based on differences in ATP hydrolysis and synthesis •  Three major types –  Slow ­oxida?ve (type I) fibers –  Fast ­oxida?ve (type IIa) fibers –  Fast ­glycoly?c (type IIx) fibers 22 Characteris?cs of Skeletal Muscle Fibers Table 8 ­1; pg. 280 23 ...
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This note was uploaded on 11/07/2010 for the course NPB NPB 101 taught by Professor Weidner/wingfield during the Spring '08 term at UC Davis.

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