After an animal dies, its muscles start to stiffen before the decomposition of t

Question

After an animal dies, its muscles start to stiffen before the decomposition of tissues relaxes the muscles again. Death is also characteized by calcium flow into the cytosol, due to breakdown of the sarcoplasmic reticulum. Which of the following would you expect to explain this muscle stiffening (i.e. rigor mortis)?

A) The myosin II heads in skeletal muscle fibers remain attached to actin filaments due to the absence of Ca2+ in these cells.

B) The ATPase activity of muscle myosin II is inhibited by the elevated Ca2+.

C) The myosin II heads in skeletal muscle cells remain attached to actin filaments due to the elevated Ca2+ in the muscle fibers.

D) Tropomyosin unfolds, preventing muscle relaxation.

E) The myosin II heads in skeletal muscle cells remain attached to actin filaments due to covalent cross-linking.

Explanation / Answer

The best explanation for the muscle stiffening after death is "the myosin || heads in skeletal muscle cells remain attached to actin filaments due to the elevated Ca2+ in the muscle fibers"(D). During the life time the cell membrane remain impermeable to Calcium. After death it become permeable to calcium molecules and it leads to the entering more Ca2+ inside the cells. These Ca2+ binds to troponin, which makes tropomyosin to expose the myosin binding sites on actin filaments. It triggers the binding of myosin to actin filaments which leads to muscle contraction.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.