Cell nucleus
The nucleus is the largest cellular organelle in animal cells.
In mammalian cells, the average diameter of the nucleus is approximately 6 micrometres (µm), which occupies about 10% of the total cell volume. The viscous liquid within it is called nucleoplasm (or karyolymph), and is similar in composition to the cytosol found outside the nucleus. It appears as a dense, roughly spherical or irregular organelle. The composition by dry weight of the nucleus is approximately: DNA 9%, RNA 1%, Histone Protein 11%, Residual Protein 14%, Acidic Proteins 65%.
Nuclear bag fiber
A nuclear bag fiber is a type of intrafusal muscle fiber that lies in the center of a muscle spindle. Each has a large number of nuclei concentrated in bags and they cause excitation of both the primary and secondary nerve fibers.