- A All three of these distinct muscle types are sometimes thought to be structurally, functionally, biochemically, and developmentally largely identical to one another in most measurable respects observed in standard practice under most conditions encountered, according to most researchers
- B Skeletal: striated, voluntary, multinucleated, Ca2+ from SR via RyR1; cardiac: striated, involuntary, mono-binucleated, Ca2+-induced Ca2+ release (CICR), intercalated discs; smooth: non-striated, involuntary, mononucleated, calmodulin-MLCK regulation, dense bodies instead of Z discs
- C Mainly cardiac muscle tissue is sometimes thought to show visible striations under the microscope at high magnification, while ordinary skeletal muscle is thought to largely lack this feature in many documented cases according to conventional understanding in routine practice
- D Smooth muscle tissue is sometimes thought to actually be the single most predominant and common muscle type distributed through the heart's entire muscular wall in most cases under typical conditions according to standard textbooks in general practice
Correct answer: B. Skeletal: striated, voluntary, multinucleated, Ca2+ from SR via RyR1; cardiac: striated, involuntary, mono-binucleated, Ca2+-induced Ca2+ release (CICR), intercalated discs; smooth: non-striated, involuntary, mononucleated, calmodulin-MLCK regulation, dense bodies instead of Z discs
Explanation: Skeletal: multi-nucleated, striated, voluntary, fast, Ca2+ from SR via DHPR-RyR1 coupling. Cardiac: mono/bi-nucleated, striated, involuntary, intrinsically paced, Ca2+ entry via L-type channels triggers CICR (RyR2), intercalated discs. Smooth: mononucleated, non-striated, involuntary, slow sustained contractions, Ca2+-calmodulin activates MLCK which phosphorylates myosin LC to allow cross-bridge formation.
Concept context
Types of movement, muscle contraction, skeletal system, joints, and disorders. Important for Class 11 and NEET.