Question

The condition in which several nuclei are present in a muscle fiber is called:
A) Coenocytic
B) Syncytial
C) Polykaryon
D) Endoduplication

Answer 1

Hint:
The cell membrane of the muscle fiber is called sarcolemma and sarcoplasm contains fine thread-like contractile structures called myofibrils. The signal for muscle contraction comes from the nerve by triggering an action potential in the sarcolemma.

Complete step by step answer:
The multinucleate cell is called syncytial or syncytium. It is caused due to multiple cell fusions of unicellular cells (these are the cells with a single nucleus only). These are caused due to many nuclear divisions without cytokinesis i.e., cytoplasm division. It is also the condition where cells are interconnected by the specialized membrane with the help of gap junctions, as in heart muscle and some smooth muscle cells. These cells are synchronized electrically in an action potential. So the condition of having many nuclei in a muscle fiber is syncytial.
The skeletal muscles are multi-nucleated i.e., having more than one nucleus. These cells are long, cylindrical, and striated. These are formed due to the fusion of embryonic myoblasts. Every nucleus regulates the metabolic requirements for the sarcoplasm around it.

Option ‘B’ is correct

Note:
An increase in cytoplasmic calcium initiates the contraction of each myofibril. The increase in calcium concentration is transient because calcium is rapidly pumped back into the sarcoplasmic reticulum by an abundant, calcium ATPase, in its membrane. Typically, the cytoplasmic calcium concentration is restored to resting levels within 30 milliseconds, allowing the myofibrils to relax.