Myocyte coordinate contraction throughout the remaining heart muscle via the electrical conduction system of the heart. Sinoatrial node activity is modulated, in turn, by nerve fibres of both the sympathetic and parasympathetic nervous systems. These systems act to increase and decrease, respectively, the rate of production of electrical impulses by the sinoatrial node. There are numerous methods employed for fiber-typing, and confusion between the methods is common among non-experts. Two commonly confused methods are histochemical staining for myosin ATPase activity and immunohistochemical staining for Myosin heavy chain (MHC) type. Myosin ATPase activity is commonly—and correctly—referred to as simply "fiber type", and
Lymph node stromal cell travel from the bone marrow or high endothelial venules of the thymus where they develop as lymphoblasts, to lymph nodes, where they mature. The primary role of lymph node stromal cells is structural. They form a scaffold for hematopoietic cells and assist their movement along it. The molecular signaling systems (chemokines) that distribute lymphocytes to appropriate localities within the lymph node (T and B cell segregation) are also created by lymph node stromal cells. Lymphocytes have receptors for such chemokines. For example, Naive T cells express the CCR7 receptor for the chemokine CCL21. and B cells exhibit CXCR5 receptors for