MSK - Muscle

Question 1

Steps of excitation-contraction coupling in skeletal muscle?

Answer 1

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!!!

Question 2

L-type channel-RyR mechanical coupling

Answer 2

In skeletal muscle, when depolarization triggers L type calcium channels in the T tubule system which trigger opening of RyR1 channels in sarcoplasmic membrane

Question 3

What is the most important determinate of peak bone mass?

Answer 3

Genetic factors - responsible for 80% of the variation.

Question 4

Which population has lower bone density - Caucasians or Africans?

Answer 4

Caucasians

Question 5

In women when does bone loss start?

Answer 5

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.

Question 6

Urinary deoxypyridinoline excretion - what does it measure?

Answer 6

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.

Question 7

Urinar hydroxyproline excretion - what does this measure?

Answer 7

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.

Question 8

Serum level of bone-specific alkaline phosphatase - what does this measure?

Answer 8

Measures osteoblastic activity.

Question 9

Serum tartrate-resistant acid phosphatase - what does this measure?

Answer 9

Measures osteoclastic activity.

Question 10

Tartrate resistant acid phosphatase, urinary hydroxyproline, and urinary deoxypyridinolone reflect osteo___ activity; which is the most reliable of the three?

Answer 10

Osteoclast

Urinary deoxypyridinoline