Introduction Skeletal muscle cells are composed of muscle fascicles muscle fascicles are composed of multi-nucleated muscle fibers muscle fibers are composed of myofibrils myofibrils contain sarcomeres, where actin and myosin filaments slide and produce contractions Muscle cell transverse tubules (T-tubules), invaginations of the plasma membrane, are juxtaposed with the sarcoplasmic reticulum’s terminal cisternae to contract T-tubules are responsible for conducting the action potential to the cisternae of the sarcoplasmic reticulum skeletal muscle triad 1 T-tubule and 2 terminal cisternae cardiac muscle dyad 1 T-tubule and 1 terminal cisterna Sliding filament theory sliding of thick and thin filaments form a contraction thick filaments composed of protein myosin anchored to M line thin filaments composed of actin, tropomyosin, and troponin actin contains binding sites for myosin tropomyosin covers these binding site grooves anchored to Z line Excitation-Contraction Coupling Action potential depolarizes plasma membrane presynaptic voltage-gated Ca2+ channels open and neurotransmitters are released from the neuron post-synaptic ligand is bound, causing depolarization of the motor end plate of the muscle Depolarization spreads to the T-tubule depolarization causes a conformational change in the voltage-sensitive dihydropyridine receptor this causes a conformational change in the ryanodine receptor (also a calcium channel protein) Ca2+ is released from the sarcoplasmic reticulum this initiates the contraction Contraction Free Ca2+ binds to troponin C this causes a conformational change and moves tropomyosin out of a myosin-binding groove Myosin releases ADP and Pi, causing displacement of myosin on actin filament this produces a power stroke and contraction shortens H and I bands, resulting in shortening between the Z lines (HIZ shrinkage) A band remains the same length Myosin head is detached from the actin filament because of binding of a new ATP molecule Hydrolysis of ATP to ADP causes myosin head to adopt a high-energy position, in preparation for the next contraction
QUESTIONS 1 of 2 1 2 Previous Next (M1.MK.15.6003) Upon depolarization of the muscle cell plasma membrane, dihydropyridine receptors in the T tubules are activated. Similarly, ryanodine receptors in the sarcoplasmic reticulum (SR) are activated leading to the release of calcium from the SR. This transient increase in calcium results in muscle contraction. Which of the following regions (Figure A) does not shorten during a muscle contraction? Tested Concept QID: 106962 FIGURES: A Type & Select Correct Answer 1 Distance from M line to the Z disc 0% (0/134) 2 Distance between the two Z discs 8% (11/134) 3 H zone 6% (8/134) 4 I band 6% (8/134) 5 A band 78% (104/134) M 1 Question Complexity E Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review tested concept (M1.MK.15.70) A scientist is studying the properties of muscle tissue. She is able to examine a single sarcomere within a myocyte, as demonstrated in Figure A. She then artificially induces the sarcomere to contract. When this occurs, which of the following sections (as identified by the correct letter in Figure A and correct name) will not decrease in length? Tested Concept QID: 106489 FIGURES: A Type & Select Correct Answer 1 Section C: A Band 15% (19/127) 2 Section C: H Zone 10% (13/127) 3 Section B: I Band 12% (15/127) 4 Section D: I Band 4% (5/127) 5 Section B: A Band 57% (72/127) M 1 Question Complexity D Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review tested concept
All Videos (2) Login to View Community Videos Login to View Community Videos Mechanism of Sarcomere Contraction Chris Robinson MSK - Muscle Conduction to Contraction D 2/16/2015 77 views 4.7 (6) Login to View Community Videos Login to View Community Videos Skeletal Muscle Conduction MSK - Muscle Conduction to Contraction D 2/16/2015 129 views 5.0 (2)