101Lecture16_2009

101Lecture16_2009 - Lecture Topic 16 The Molecular Basis of...

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Unformatted text preview: Lecture Topic 16 The Molecular Basis of Contraction Excitation-Contraction Coupling Twitches Muscle Tissue Categories Figure 8.1 Skelel'al Muscle Organization Muscle fiber {a single muscle cell} Dark A band Light I hand Myoflhrll Figure 8.2 .m.,;.,..._,.. Cyfoskeletal Organization of a Myofibril Cross Thin Thick bridge filament filament M line 2 line A band 1 band Portion of myofibril Thick Thin 5‘ filament filament |(— Sarcomere—fl A band I band Cross bridges M line H gene 2 line (c) Cyloskelelal components of a myoflbrll Figure 8.2 Contractile Proteins: Thick Filaments mun-binding site Myosin ATPase site Tail k (a) Myoeln molecule Cross bridges (b) Thick filament 0 Thick fi aments are made up of myosin dimers. Figure 8.4 Thin Filaments ©©©®% anfiw AciIn molecules cross ””99 I Composed of m mlecules . 0 Binding sites occupied by regulatory proteins - Tropomyosin - Troponin Figure 8.5 How do Thick and Thin Filaments Induce Confracfion? Cross-Bridge Formation and Acfivify The Thick and Thin Filameni's “Slide” Sarcomere f—A'—'fi Z line H zone I hand A band Z line Relaxed Contracted Fi are 8.7 ~—_J- - -| - ' 9 Sam shorter Thuckfllament Thlnillament Excitation-Contraction Coupling Calcium is Necessary for Contraction Surlace membrane 01 muscle fiDBI‘ Transverse (T) K—l hand—)K—A band—m—I bard—) Fig 8.9 0 Stored in the sarcoplasmic reticulum 0 The SR is closely associated with T-tubules and contractile proteins Calcium Influxes When the Muscle Depolarizes .MWWMIIM [mammalian-ammun- 0 Depolarization occurs first at the motor endplate 0 Action potential 0 Lateral spread of the action potential 0 The T-tubule - Invagination - At the sarcoplasmic reticulum - The AP traverses into the T-tubule Figure 8.11 Bmmmumwem mum-autumnal“ mnmunmmw mumhmmnm. The T-Tubule MWh o Allows the depolarizationmt'o elicit Ca2+ release 0 Dihydropyridine receptor (DHPR) - Found along the T-tubule - Voltage sensitive. Connected to Ryanodine Receptors Calcium Influx Cinnamon-Malamu- "Mlflmmmmfl mummm mmmmnmm iflwmhflfl- Mm mnnlmmwl—uuw' 0 DHPR aci'ivai'ion o Ryanodine recepfor activa‘l'ion 0 Ca2+ influx Figure 8.11 lmmmummum mummy-unfit“ mun-aluminum mnm—uhmumlrm. Cu“ is fhe Link befween Excifa’rion and Contracfion Lonulludlml m clwu-ucliund m mmummmmmwmmmmkmwmwmwm B mamam. 0’] EM ll mmmmmcabismm a WW‘MWtW.Nflmlmmflmthmwmflmflmdm Figure 8.6 Wunflmm II wmdmmmmnmmmmummmmwmmmmmm. Cross Bridge Cycling Requires ATP @9909 6:.» Ham.» :99 ‘ ' 1— "" fl Emmil’afiilbynwn ' hTPueszmP.mIahallwledio mohanorwmmmm imow‘mmm). 0009’ A? W W m W:Wmmmm mmhhokwmlmfinwbfleolnw Miomilnumblldoe:awabfldw WWW-RV mmmtqua rummaging: 1). Flush lTP “MI. "’0'... no no (mar nun.) J“ an lemwzrnonesn ATP mtfllerdeamLmu-idw Wham-1mm. @ mma’finiouodonnmlon: wmnwmmmnm. Mumi’oworaimolm millage-wonmbem mmmfimmm flumIMrmm. Figure 8.12 Cross-Bridge Cycling 0 During a confrac’rion, rhe cross bridges form, break fhen reform. I Requiremenrs: - Depolarization 0 As long as we have rhese condi’rions, a con‘l'rac’rion could occur Actin molecules in thin myofilement ...._- a .1 Blnding:Myoein ' “ "d cross hridgehindsto acfln molecule. Power stoke: Cross bridge bends. pulling thin myofilamem Inward. a Detachment: Cross bridge detaches at end of power eiroke end relume 10 original conformation. 9 Binding: Cross bridge binds no more dieiel ec1in molecule: cycle repeats. (a) Single cross-bridge cycle Fig 8.8 s“OPPiI'Ig Contraction G19) ' Ace’fvlcholine is removed by an esferose Figure 7.5 51'Opping Com‘racfion . Cd” is removed mm ”‘3 cyfoplasrn by Pumps , Similar to Figure 8.11 Stopping Confracfion o Ca2+ is removed from the ‘. cyfoplasrn by pumps ’ Similar to Figure 8.11 The Mechanics of Muscle Contracfion Muscle Twitch 0 We can obtain a weak _ contraction From a single fiber 0 Short in duration 0 By itself, doesn’t really do much IOI'I Tens é Action potential Membrane polanlial [HIV] 0 I -TO 1-: mu: 1 Figure 8.13 if so 100 Time {msecl Stimulation Muscle Arrangement Muscle 0 Recall that muscle fibers are arranged in bundles. These are surrounded by connective tissue Figure 8.2 Muscle fiber (a single muscle cell) Connective tissue 0mm “I'M-mm Arrangement of Motor Units 0 A single motor neuron may innervate several muscle fibers within a single muscle KEY E =Motorunit1 o The grouping is $332323: considered a motor unit. Figure 8.16 Contraction Strength of Small Versus Large Motor Units Relatlve strength of whole-muscle contraction Relative strength of whole-muscle contraction 0 1 2 3 4 5 O 1 2 3 4 5 Number oi motor units recruited Number oi motor units recruited (3) Recruitment of small motor units (b) Recruitment of large motor units Figure 8.17 Twitches and Summation flamflaflberls muted afterlrusoompleielyrelamd. unmodmlsfllosam 0W _ magnimdaaamafimtwm. summammmmd mnhacfimhmnasm'm (a) Noemi-nation (b) “when sumaflan (c) Tetanus Figure 8.18 ...
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