Plasma cells are differentiated or mature B cells capable of producing antibodies against a particular foreign substance. B cells are stimulated to differentiate into plasma cells when it binds to two receptors of helper T cell; having the T cells "help" the B cells to differentiate to plasma cells. These T cells have the antigenic information passed to them by antigen presenting cells such as dendritic cells and these will be passed to the B cells and plasma cells will produce antibodies against this specific antigen.
Explanation: We have two parts to our nervous system. The central nervous system and the peripheral nervous system. The CNS is located in the brain and spinal cord the PNS is the nerves and ganglia outside of those.
Dr. Fisher was lying on the back thus postmortem staining can be observed on his back. But if the body was moved after death then postmortem staining can also be observed on different parts of the body that can be the front part.