anatomy and physiology mcqs

Question #148

Which of the following is true of the transverse tubular system in cardiac muscle?

The transverse tubules are membrane invaginations found in both skeletal and cardiac muscle cells. They are notably absent, however, in atrial muscle. The transverse tubules permit propagation of the depolarizing action potential wave into the interior of the cell.

Ca2+ influx through L-type Ca2+ channels present in the tubular membranes are key in intiating Ca2+ induced Ca2+ release (CICR) via the ryanodine receptor ion channel, present on the sarcoplasmic reticular membrane. Evidence suggests that the spread of depolarization from transverse tubule to transverse tubules may be important in action potential propagation. These structures cannot therefore be considered to be equivalent to the surface membrane.

See A Thinking Approach to Physiology, pages 45 - 50.

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