Isolated cardiac myocyte in culture undergoing periodic contractions Courtesy of Jan Lammerding Used with permissi Structure of dle mage removed due to copyright considerations
undergoing periodic contractions Structure of muscle Courtesy of Jan Lammerding. Used with permission. Isolated cardiac myocyte in culture 1� Image removed due to copyright considerations
Skeletal (striated)and smooth muscle O (b)Smooth muscle Temporal patterns of muscle contraction Single twitch Periodic sequence of excitations Fused tetanus(Fmav) 日 Unfused Time(sec)
Skeletal (striated) and smooth muscle� Temporal patterns of muscle contraction • • • max) l (a) Skeletal muscle (b) Smooth muscle Single twitch Periodic sequence of excitations Fused tetanus (F 2
Tension-length curves for a muscle fiber (relaxed and maximally stimulated) =(0+阝) Passive Length l∥ Hills equation Empirically determined force-velocity relationship obtained from macroscopic measurements vF/Fv v/vmax 1-(F/F F1-(F/F) C(F/Fma) Fmax(Fmas/F)+C
Tension-length curves for a muscle fiber (relaxed and maximally stimulated) l Empirically determined force-velocity relationship obtained Hill’s equation from macroscopic measurements v vmax = 1- (F Fmax) 1+ ( max) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.2 0.4 0.6 0.8 1 v/vmax F/Fmax or P/Pmax vF vmaxFmax = 1- ( CFF (Fmax F) +C F/Fmax vF/Fmaxvmax F Fmax) 3�
ource of ener rgy for muscle口 Hydrolysis of adenosine triphosphate(ATP) creating adenosine diphosphate(ADP) ATP →ADP+P ATPase △G=AGn-67l ATP ADPIIP or approximately -25 kT(displacement -5 nm) Power/weight same as an automobile engine
Source of energy for muscle� Hydrolysis of adenosine triphosphate (ATP) creating adenosine diphosphate (ADP): ATP æ Æ actomy æææsin ADP + Pi ATPase Ê [ATP] ˆ DG = DG0 - kT lnÁ ˜ Ë [ADP][ ] Pi ¯ or approximately -25 kT (displacement ~ 5 nm) Power/weight ~ same as an automobile engine 4
A rise in cytosolic Ca2+ triggers muscle contraction(part D) Sarcomere Myofibrils Sarcoplasmic reticulum Transverse tubule Plasma membrane Terminal cisterna of SR A rise in cytosolic Ca2+ triggers muscle contraction(part Il Step 1: An excitation signal travels along the efferent nervous pathways towards the muscle Qee Step 2: The excitation signal de-polarizes the cell membrane Step 3: The potential triggers the release of calcium into the sarcoplasmic matrix surrounding the filaments of the motor Step 4: This removes the hindrance( tropomyosin)for interactions between actin and myosin filaments through chemical. mechanical and electrostatic actions. Step 5: The stepping action of myosin along the adjacent actin filament causes the two to slide relative to each other reducing the length of the sarcomere, producing contraction. Step 6: Sequestration of calcium ions in the sarcoplasmic reticulum(ATP-dependent) switches the contraction activity
A rise in cytosolic Ca2+ triggers muscle contraction (part I) 2+ Step 1: An excitation signal travels along the efferent nervous pathways towards the muscle. Step 2: The excitation signal de-polarizes the cell membrane. This allows spread of the action potential along the Step 3: The potential triggers the release of calcium into the unit. Step 4: chemical, mechanical, and electrostatic actions. Step 5: The stepping action of myosin along the adjacent Step 6: reticulum (ATP-dependent) switches the contraction activity off. A rise in cytosolic Ca triggers muscle contraction (part II) sarcoplasmic reticulum. sarcoplasmic matrix surrounding the filaments of the motor This removes the hindrance (tropomyosin) for interactions between actin and myosin filaments through actin filament causes the two to slide relative to each other, reducing the length of the sarcomere, producing contraction. Sequestration of calcium ions in the sarcoplasmic 5�