MCP 29: Muscles I Flashcards
muscle fiber
group of myofibrils covered in sarcolemma
t-tubules
deep pits in sarcolemma continuous with the extracellular environment
terminal cisternae of the sarcoplasmic reticulum
found next to the t-tubules
sarcoplasmic reticulum
high concentration of calcium bound by calsequestrin
potassium and t-tubules
limited extracellular space limits K+ ability to clear during repolarization, leading to elevated extracellular K+ and reducing the rate of K+ efflux from the cell, high extracellular K+ means that the RMP of the cell is depolarized.
Cl- leak channels and skeletal muscle
help cell repolarize
myotonia
skeletal muscle genetic disorder resulting from defect in Cl- leak channels
excitation coupling
process by which AP in the skeletal muscle generates a muscular contraction 1.) AP sent along muscle membrane down T-tubules into triad 2) depolarization reaches the voltage sensitive L-type Ca2+ channel and activates it 3.) the L-type channel tickels and activates the ryanodine receptors 4.) Ca2+ released into the sarcoplasm
sarcoplasm
cytosol of muscle
calsequestrin
keeps Ca2+ levels high SR with help from Ca2+ ATP pump
hierarchy of muscle anatomy
muscle-myofibers (cells with many nuclei)-myofibrils (long stretches of sarcomeres arranged in series)-alternating thin and thick filaments that form striations
thin filaments
made up of actin, tropomyosin and troponin
thick filaments
made of myosin, do no move during muscle contraction, thin filaments slide over it
A-band
encompasses the entire length of myosin, stays the same length during contraction
I-band
contains only actin, shrinks during contraction
H-band
myosin only, shrinks with contraction
Z-line
attachment point for actin filament, from Z-line to Z-line is one sarcomere
M-line
midpoint of sarcomere, holds myosin filament in place
actin
individual global (G) actin units line up to create filamentous (F) actin filaments, two F filaments wrap around each other, tropomyosin found along length of active sights
troponin T
attaches troponin complex to tropomyosin
troponin I
lock in place tropomyosin to inhibit actin/myosin interaction
troponin C
binds Ca2+, causing tropomysoin to move out of the way so actin, myosin interaction can occur, 4 actin binding sites, two high affinity sites occupied all the time, the other two low affinity sites allow sliding when calcium increases
myosin
made of two chains of light myosin and 2 heads of heavy myosin, two hinged regions, head has ATP and actin binding sites
cross linking
1.) ATP binds to myosin head, cross linking released 2.) ATP hydrolyzed into ADP and Pi, causing myosin head to be perpendicular to actin filaments 3.) Ca2+ binds to troponin C and changes conformation of troponin/tropomyosin complex Myosin can now attach to actin 4.) ADP and Pi released and power stroke occurs. Myosin head moves 45 degrees and moves actin toward M-line. 5.) Ca2+ removed from sarcoplasm by Ca2+ ATPase, insufficient amount of Ca2+ to bind troponin C.
how much does the sarcomere shorten during the power stroke?
1 micrometer
speed of power stroke
depends on speed of ATPase on the myosin head
strength of cycle
depends on number of cross bridges formed, related to amount of calcium
rigor mortis
actin and myosin filament remain attached because not APT to allow the release of the two components `
sources of fuel for muscle contraction
glycolysis, Krebs cycle and creatine phosphate
