The nervous system is made up of nervous tissue. The nervous tissue is special in that it contains:
1/ neurons /neurons and
2/ glial cells.
The nerve cells convey, process and store (memory) information through electrical and chemical processes. In this context, it is particularly important how different neurons are interconnected with each other in larger and smaller networks (the patterns - circuits - that different neurons form with each other).
The glial cells have long been perceived as supporting cells for the neuron; This is partly by mechanically acting as support, isolation and protection, and partly by relieving the neuron of certain tasks within metabolism. Recent research suggests that certain glial cells may be directly involved in information dissemination and memory storage.
Like most other body tissues, the nerve tissue contains blood vessels and, outside the cells, a fluid-filled space, the so-called extracellular space. But there are big differences between PNS and CNS in how the friend components are arranged.
In PNS, nerve fibers and cell bodies are surrounded by connective tissue. The extracellular space is comparatively spacious and the cells are often more than 1 micrometer (= 1/1000 mm) apart (this does not sound much, but is a considerable distance in the world of cells). In the PNS, there are also lymphatic vessels.
In the CNS tissue, connective tissue and lymphatic vessels are missing. The extracellular space is very narrow and the cells are tightly packed together at a distance of only 1/100 micrometer.
The parts of the CNS tissue that lie outside the nerve cell bodies, glial bodies and blood vessels form, as it appears after the use of ordinary light microscopic technique, a dense filamentous unstructured mass, the so-called nerve blanket or neuropil.