Question

11. The figure below shows tension recorded in two different skeletal muscles: a control (solid line), and one that was injected with caffeine (dashed line). Arrows show the arrival of action s loc potentials at both muscles ming of stimulus, contraction and relaxation phases are the same). We know that caffeine n channels. Based on this data, please identify which ion channels are affected, explain why tension builds faster in the injected muscle, and identify the mechanism used to build tension. (5) shift affects io ft Time 12. On the same axis, graph and label two myograms: a single twitch contraction for a Type 1 (slow) fiber, and one for a Type 2X (fast) fiber: Label the axes, and stimulus, lag, contraction, and relaxation phases with appropriate relative lengths and amplitudes. THEN explain what Ca? ions are doing in the contraction phase versus the relaxation phase (10)

Answer 1

11. The action of caffeine is on the calcium on application of a caffeine there is calcium ions release from the sarcoplasmic reticulum

High concentrations of caffeine can increase Ca2+ release from the sarcoplasmic reticulum (SR), increase tension development in single contraction, and almost completely reestablish maximum tension development in fatigued single myofibers by restoring calcium release from the SR to nonfatigued levels

12 During the contraction phase Ca is released from the SR

release of ca from storage in the SR initiates contraction, sustained by ATP. Ca ions remain in the sarcoplasm to bind to troponin, which unshields the actin-binding sites and ATP drives the cross-bridge cycling and the pulling of actin strands by myosin, the muscle fiber will shorten

Muscle contraction usually stops when the voltage-gated calcium channels in the SR closes. Ca++ ions are then pumped back into the SR, which causes the tropomyosin to reshield the binding sites on the actin strands.

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