Muscular and skeletal physiology (417-419)

Question 1

name the four states of myosin/actin complex and the drivers of these states

Answer 1

1. cocked state: ATP hydrolysis cocks myosin head
2. cross-bridged state: binding of Ca2+ to troponin on tropomyosin allows myosin head to bind actin at myosin binding site
3. power stroke: caused by release of ADP and Pi
4. release of actin from myosin heads: binding of new ATP releases actin-myosin bond

Question 2

name the two calcium receptors involved in calcium-induced calcium release; which one is found on the sarcolemma? which is found on the SR?

Answer 2

dihydropyridine receptor found on sarcolemma

ryanodine receptor found on sarcoplasmic reticulum

Question 3

name the steps of muscle conduction to contraction from nerve impulse to contraction of sarcomere

Answer 3

1. AP reaches neuromuscular junction => Ca2+ mediated neurotransmitter release
2. neurotransmitter causes muscle depolarization
3. depolarization goes through T tubule
4. DHP receptor senses depol. and mechanically activates ryanodine receptor => SR conf. change
5. Ca2+ released binds troponin
6. myosin binding sites free =>powerstroke

Question 4

define these:

H band, I band, A band, Z line

Answer 4

H band= length of space consisting only of myosin
I band= length of space consisting only of actin
A band= length of myosin (always constant)
Z line= line perpendicular to actin filaments to which they are anchored

Question 5

describe type 1 muscle fibers (speed of twitch, color, special changes in organelle concentrations)

Answer 5

type 1 muscle fiber= slow twitch, red, high myoglobin and mitochondria concentrations (high oxidative phosphorylation)

Question 6

describe type 2 muscle fibers (speed of twitch, color, special changes in organelle concentrations)

Answer 6

type 2 muscle fiber= fast twitch, white, low myoglobin and mitochondrial concentration (high anaerobic glycolysis)

Question 7

what are the two types of bone formation

Answer 7

endochondral ossification and membranous ossification

Question 8

describe endochondral ossification

Answer 8

chondrocytes lay down cartilage (type 1 collagen), which is then converted to woven bone and later to lamellar bone (in axial and appendicular bones and base of skull)

Question 9

describe membranous ossification

Answer 9

woven bone is lain down directly without cartilage formation and is later converted to lamellar bone (in calvarium and facial bones)

Question 10

what is the developmental origin of osteoblasts

Answer 10

mesenchymal stem cells in periosteum

Question 11

what is the developmental origin of osteoclasts

Answer 11

osteoclasts differentiate from monocytes/macrophages

Question 12

what two molecular functions do osteoblasts perform that promote bone formation

Answer 12

1. secrete collagen

2. catalyze mineralization

Question 13

are osteoclasts mononucleated or multinucleated?

Answer 13

multinucleated

Question 14

what two main substances do osteoclasts secrete that allows them to reabsorb bone?

Answer 14

1. collagenase

2. acid (carbonic anhydrase is one source)

Question 15

what does low and/or intermittent levels of PTH promote

Answer 15

anabolism of bone

Question 16

what does high and chronic levels of PTH promote

Answer 16

catabolism of bone (osteitis fibrosa cystica)

Question 17

how does estrogen protect against osteoporosis

Answer 17

estrogen inhibits osteoblast apoptosis and promotes osteoclast apoptosis