The nuclear membrane, also known as the nuclear envelope, consists of two lipid bilayers that separate the nucleoplasm from the cytoplasm. This enables storage of the majority of the human genome, as well as compartmentalization of highly regulated nuclear processes such as transcription. The outer membrane is continuous with the endoplasmic reticulum, whereas the inner membrane and the underlying nuclear lamina, containing intermediate filament proteins called lamins, serve as an anchoring site for chromatin. The space between the inner and outer membrane is referred to as the perinuclear space. Nuclear pore complexes are distributed throughout the membrane and enable selective transport of large molecules between the nucleus and cytoplasm, while allowing free diffusion of small molecules and ions.
The nuclear membrane is easy to recognize as its staining appears as a thin circle around the nucleus. However, the nuclear membrane is not perfectly smooth and sometimes it is also possible to see the folds of the membrane as small circles or dots inside the nucleus, which can easily be mistaken for nuclear bodies. The nuclear membrane breaks down upon entry into mitosis and reforms in the last stage of mitosis.
Read more about the proteome of the nuclear membrane.