Nervous Tissue

Nervous tissue is responsible for carrying out all the informational signaling in our bodies. Our brain is made of nervous tissue, and it can choose to tell our muscles (via the spinal cord and nerves) to carry out certain actions. Our sensory systems all provide information to our brains via nervous system cells as well.

There are two main cell types in the nervous system: neurons and glia (your book calls the second type neuroglia, but "glia" is fine). Neurons are the electrically active, signaling cells of the nervous system. Glia are the support cells, and they have many, many other functions that we will discuss when we get to the nervous system.

Nervous tissue receives nutrients from the blood, but not all blood borne factors can enter nervous tissue... nervous tissue lies within a protective ensheathment which creates the blood-brain barrier. However, nervous tissue can still be considered vascularized.

The neurons of nervous tissue are unable to divide-- ever. Once they die, they can thus never be replaced. The glia are able to reproduce, but cannot take over the functions of neurons.

Although when one looks at nervous tissue (see Figure 5.31 in your textbook) it looks like there are a lot of spaces where extracellular material could be present, that is NOT the case. In fact, neurons (and glia) can send out so many tiny, tiny branches of their cells that all the space you see is actually full of neuronal (and glial) processes.