Connective tissue is one of the four types of biological tissue that support, connect, or separate different types of tissues and organs in the body. It develops from the mesoderm. The other three types are epithelial, muscle, and nervous tissue. Connective tissue is found in between other tissues everywhere in the body, including the nervous system. In the central nervous system, the three outer membranes (the meninges) that envelop the brain and spinal cord are composed of connective tissue.
All connective tissue apart from blood and lymph consists of three main components: fibers (elastic and collagenous fibers), ground substance and cells. (Not all authorities include blood or lymph as connective tissue.) Blood and lymph lack the fiber component. All are immersed in the body water.
The cells of connective tissue include fibroblasts, adipocytes, macrophages, mast cells and leucocytes.