Columnar epithelia usually imply very active secretion and absorption. A good example is found in the mammalian small intestine. In connective tissues , the cells are typically not touching. Unspecialized connective tissue is often referred to as loose connective tissue . Its function is to bind and support other tissues, and you can think of it as the packing material of the body.
Collage is secreted into the tissue by fibroblasts.
Glial cells are especially important because they provide the myelin wrappings of nerve cells, which speeds up nervous system activity in vertebrates. Invertebrates do not have myelin. As Hugh has already told you, special ion channels in neuronal membranes allow nerve signals to transmit information around the body using electrical impulses. When one examines a neuron under a microscope, one can easily see the numerous long processes. Therefore, a major part of differentiation as a neuron involves specializations of the cytoskeleton that supports these processes.