Q50.
What are the differences between smooth, cardiac, and skeletal muscle in terms of structure and regulation?
Show answer & explanation
Answer: B. Skeletal: striated, voluntary, multinucleated, Ca<sup>2+</sup> from SR via RyR1; cardiac: striated, involuntary, mono-binucleated, Ca<sup>2+</sup>-induced Ca<sup>2+</sup> release (CICR), intercalated discs; smooth: non-striated, involuntary, mononucleated, calmodulin-MLCK regulation, dense bodies instead of Z discs
Why: Skeletal: multi-nucleated, striated, voluntary, fast, Ca<sup>2+</sup> from SR via DHPR-RyR1 coupling. Cardiac: mono/bi-nucleated, striated, involuntary, intrinsically paced, Ca<sup>2+</sup> entry via L-type channels triggers CICR (RyR2), intercalated discs. Smooth: mononucleated, non-striated, involuntary, slow sustained contractions, Ca<sup>2+</sup>-calmodulin activates MLCK which phosphorylates myosin LC to allow cross-bridge formation.