The library (from Greek karyon, core and theke, envelope, box) is a envelope formed by two lipoprotein membranes whose molecular organization is similar to other cell membranes.
Between these two membranes there is a narrow space called the perinuclear cavity. The outer face of the library, in some parts, communicates with the endoplasmic reticulum and often has ribosomes attached to its surface. In this case, the space between the two nuclear membranes is a continuation of the internal space of the endoplasmic reticulum.
Pores of the library
The library is punctured by thousands of pores, through which certain substances enter and leave the nucleus.
Nuclear pores are more than just openings. In each pore there is a complex protein structure that functions as a valve, opening to pass certain molecules and then closing. This way the library can control the entry and exit of substances.
The inner face of the library is the nuclear lamina, a supporting protein network. The nuclear lamina participates in the fragmentation and reconstitution of the library, phenomena that occur during cell division.