Cell nucleus
Cell nuclei contain most of the cell's genetic material, organized as multiple long linear DNA molecules in a complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these chromosomes are the cell's nuclear genome and are structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, therefore, the control center of the cell. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm, and the nuclear matrix (which includes the nuclear lamina), a network within the nucleus that adds mechanical support, much like the cytoskeleton, which supports the cell as a whole.
Medullary command nucleus
The medullary command nucleus (MCN), also called the "pacemaker nucleus", is a group of nerve cells found in the bodies of weakly electric fish. It controls the function of electrocytes by regulating the frequency of electrical impulses. Signals originating in the MCN are transmitted to electrocytes, where changes in ion concentration cause electrical charges to be generated. The nucleus both sends and receives signals, thereby acting as a regulator and central processor for the electro sensors in the fish’s body. Inputs into the MCN originate in the mesencephalic precommand nucleus, thalamic dorsal posterior nucleus, and toral ventroposterior nucleus. All of these nuclei have dense projections into the MCN, with the exception of theToral Ventroposterior nucleus, which contain only a ventral edge projection.