Question

(part 1) Give a physiologically sound explanation why contraction velocity is faster than relaxation velocity.

A. Ca2+ reuptake by the lateral sacs is active and requires the use of pumps while Ca2+ release from the lateral sacs is passive and does not require the use of pumps.

B. Ca2+ reuptake by the lateral sacs is passive and requires the use of pumps while Ca2+ release from the lateral sacs is active and does not require the use of pumps.

C. Ca2+ reuptake by the lateral sacs is passive and does not require the use of pumps while Ca2+ release from the lateral sacs is active and requires the use of pumps.

D. Contraction velocity is NOT faster than relaxation velocity.

(part 2)  Explain the mechanism of temporal summation.

A. Increasing the strength of a single stimulus results in more Ca2+ in the cytosol which results in more cross-bridging and a greater contraction force.

B. Increasing the strength of a single stimulus results in more Na+ in the cytosol which results in more cross-bridging and a greater contraction force.

C. Increasing the frequency of stimuli results in less time for Ca2+ to be returned to the lateral sacs and when the following stimulus occurs, the Ca2+ released from the lateral sacs is added to the remaining Ca2+ in the cytosol which results in more cross-bridging and a greater contraction force.

D. Increasing the frequency of stimuli results in less time for Na+ to be returned to the lateral sacs and when the following stimulus occurs, the Na+ released from the lateral sacs is added to the remaining Na+ in the cytosol which results in more cross-bridging and a greater contraction force.

Answer 1

Q1) A. Ca2+ reuptake by the lateral sacs is active and requires the use of pumps while Ca2+ release from the lateral sacs is passive and does not require the use of pumps.

Q2) C. Increasing the frequency of stimuli results in less time for Ca2+ to be returned to the lateral sacs and when the following stimulus occurs, the Ca2+ released from the lateral sacs is added to the remaining Ca2+ in the cytosol which results in more cross-bridging and a greater contraction force.