Question

What characterizes nuclear bag intrafusal muscle fibers?

a) Central nuclei in a bag-like arrangement
b) Peripheral nuclei in a chain-like arrangement
c) Lack of nuclei
d) Cross-striations in the sarcomere

Answer 1

Nuclear bag intrafusal muscle fibers are characterized by a central, bag-like arrangement of nuclei, and they have a role in sensing changes in muscle length within the muscle spindle.

Step-by-step explanation:

Nuclear bag intrafusal muscle fibers are characterized by having their nuclei in a central, bag-like arrangement. These fibers, along with nuclear chain fibers, make up the intrafusal fibers in skeletal muscles, which are important components of the muscle spindle that sense changes in muscle length. Unlike the multi-nucleated skeletal muscle fibers that have the nuclei on their periphery, nuclear bag fibers display a more centralized pattern of nuclei. These intrafusal fibers do have striations due to the regular arrangement of actin and myosin filaments, which is a characteristic of striated muscle tissue. The striations, however, are not relevant to the distinction between nuclear bag and nuclear chain fibers; the key difference lies in the placement of the nuclei.