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Fxcitation-Conlraclion Coupling

MUSCLE PHYSIOLOGY

HART 3.1 COMPARISION OF MUSCLE STRUCTURE AND FUNCTION

	Skeletal Musclc	Cardiac Musclc	Smooth Musclc
Słructure
Morphology	Long; cylindrical	Branched	Spindle or fusiform
Nuclei	Multiple; locatcd pcriphorally	One (sometimes two); located centrally	One; located centrally
Sarcomere	Yes; striated pattcm	Ycs; striated pattern	No
T tubules	Ygs; forms triad with sarcoplasmic retk ulum	Yes; forms dyad with sarcoplasmic reticulurn	No; cavcolae
Hectrical roupling of cells	No	Yes; inten alated disc-s contain gap junctions	Yes; gap junctions
Regeneration	Ycs; via satcllitc cells	No	Yes
Mitosis	No	No	Yes
Physiology
ExtracellularCa^Jł requircd for contraction	No	Yes	Yes
Regulation of cross-bridge iormation	Ca^J 1 binding to troponin	Ca-’ binding to troponin	Ca"-calmodulin activation of myosin kinase and phospborylation of myosin
Control of contraction	Motor ncurons	Autonomie nerves; /3adrcnergic agonists	Autonomie nerves; hormones
Summation of twitches by mcrcased stimulus trequency	Yes	No*	Yes
Tension varies with filament overtap	Ycs	Yes	Yes

Major ditferences in structure and function ot skclctal. cardiac and smooth musclc aro indicted.

•Cardiac rnusr lf* rannot Im- tetani/ed, but the /orce of contraction will incrcase at high slimulus frequency Ihh aust* of an increase in intracel-tiar |Ca**|, a phenomenon tcrmcd •'Trcppc."

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