Flashcards in MSK - Muscle Deck (10)
Steps of excitation-contraction coupling in skeletal muscle?
1. Depolarization of cell membrane triggers L-type Ca channel opening in myocyte's T tubules
2. RyR1 calcium channels in the sarcoplasmic membrane open
3. Calcium is released from sarcoplasmic reticulum; there is NO flux across the L type calcium channel
4. Calcium binds troponin C, allowing actin and myosin to bind.
5. ATP bound to myosin is hydrolyzed; contraction occurs
NOTE: SKELETAL MUSCLE DOES NOT REQUIRE CALCIUM TO ENTER FROM THE EXTRACELLULAR SPACE TO CAUSE CALCIUM RELEASE FROM WITHIN THE CELL.
CCBS DO NOT AFFECT SKELETAL MUSCLE!!!
L-type channel-RyR mechanical coupling
In skeletal muscle, when depolarization triggers L type calcium channels in the T tubule system which trigger opening of RyR1 channels in sarcoplasmic membrane
What is the most important determinate of peak bone mass?
Genetic factors - responsible for 80% of the variation.
Which population has lower bone density - Caucasians or Africans?
In women when does bone loss start?
Reaches a peak in 20s and 30s and then starts to progressively decline; most subjects lose a predictable amount of bone mineral density per year.
Accelerates considerably with menopause because of declining estrogen levels.
Urinary deoxypyridinoline excretion - what does it measure?
Measures osteoclastic activity. Released into circulation when bone is absorbed by osteoclasts.
Pyridinoline covalently cross-links collagen fibers and these cross-links are the most commonly used method in assessing osteoclastic activity.
Urinar hydroxyproline excretion - what does this measure?
Measures osteoclastic activity, along with urinary deoxypyridinoline.
Pyridinoline covalently cross-links collagen fibers. Breakdown of collagen releases hydroxyproline. This is not an ideal measurement of osteoclastic activity because several common meat products cause high hydroxyproline urine concentration.
Serum level of bone-specific alkaline phosphatase - what does this measure?
Measures osteoblastic activity.
Serum tartrate-resistant acid phosphatase - what does this measure?
Measures osteoclastic activity.