Question

Draw one labeled graph of 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 Ca²⁺ ions are doing in the contraction phase versus the relaxation phase.

Answer 1

When there is action potential the membrane potential changes so that the voltage gates calcium channels open and some calcium enters the cell known as trigger calcium which stimulates the sarcoplasmic reticulum to release lots of calcium. This released calcium then goes to sarcomere and it exposes the active site on Actin by binding to Troponin allowing myosin head to form cross bridge with actin.

And thus causes contraction.

When the calcium detaches from Troponin the active site of actin is hid thus causing relaxation