L/D 4: muscle

Question 1

T/F when the crossbridge is bound to actin and ADP· Pi , it is attached to myosin and perpendicular to the long axis of the myofibril

Answer 1

true

Question 2

T/F if a weight hanging freely from a resting muscle is lifted by the muscle, the tension in the titin filaments will decrease

Answer 2

true
because muscle is shortening, tension in titin (anchoring thick filament) will decrease – so will all contributions to the parallel elastic component

Question 3

T/F, in a graph of passive and active tension vs length, the twitch tension of the muscle at any given length can be determined

Answer 3

false
the graph charts maximum possible active tension at any given length (tetanic tension)… not twitch tension, which is likely to be much lower

Question 4

T/F the amount of Ca+2 released from the sarcoplasmic reticulum is less during a twitch than during a tetanic contraction

Answer 4

false

the same amount is released in a tetanic contraction, the VGCa++ gates are just kept open longer

Question 5

how does twitch tension-time diagram change if…actomyosin ATPase activity is reduced

Answer 5

reduced rate of tension increase
reduced peak twitch tension
same overall timeframe
(because cross-bridges moving slower)

Question 6

how does twitch tension-time diagram change if… muscle is held at 125% rest length?

Answer 6

reduced rate of tension increase
reduced peak twitch tension
same overall timeframe
(because Lrest is where max force can be generated)

Question 7

how does twitch tension-time diagram change if… SR ATPase activity is reduced?

Answer 7

same rate of tension increase
higher peak twitch tension
longer twitch timeframe
(because SR ATPase resequesters Ca++)

Question 8

how does twitch tension-time diagram change if… the stiffness of the series elastic component is increased?

Answer 8

increased rate of tension increase
higher peak twitch tension
same twitch timeframe
(because twitch tension would be more similar to max (tetanic) tension)

Question 9

adding sarcomeres in series will increase:
A. contraction velocity
B. maximum isometric tension

Answer 9

contraction velocity
(more units shortening at same time)

Question 10

adding sarcomeres in parallel will increase:
A. contraction velocity
B. maximum isometric tension

Answer 10

maximum isometric tension

more cross-bridges pulling