Nervous system introduction
Introduction to neural cell types
In this video, I want to introduce the different types of neural cells. The word "neural" or the prefix "neuro" just refers to the nervous system, so that neural cells are cells of the nervous system. Neural cells work with all the other cell types of the body to produce the amazing range of functions of the nervous system, including consciousness, social interactions, cognition, emotion, movement, sensory perception, and regulation of other functions, such as circulation, respiration, and digestion. Neural cells are divided into two big categories. The first are neurons, which were traditionally called nerve cells. And the second are glia. Now, these can also be called neuroglia or glial cells. That all means the same thing. Neurons are named from a Greek word for nerve, while glia are named from a Greek word for glue, because they were once thought to do little except glue neurons together. The structure of the nervous system is divided into two main parts. The first part is mainly made up of the brain in the head and the spinal cord in the spine. And this part of the nervous system is called the central nervous system. The other part of the nervous system is called the peripheral nervous system. And that's made up mostly of nerves, these long, stringy structures that come out of the brain and the spinal cord. And they go all over the body, like down into the arms, and down into the legs, and into every part of the body. And we'll cover a lot more in detail about neuroanatomy in other videos. But I just need to bring up the central and peripheral nervous system because the neural cells are divided up differently amongst the different systems. Calling neurons nerve cells is a little problematic because these structures in the peripheral nervous system called nerves are made up of neurons. But they also contain glial cells. And they contain a number of other cells that aren't neural cells at all. However, you'll often hear people refer to neurons as nerve cells because that was the traditional name for them. Neurons are found both in the central nervous system, the brain and the spinal cord, and the peripheral nervous system, in the nerves. But the different types of glial cells are found only in one or the other. Most neural cells are derived from populations of cells called neural stem cells or neural crest cells. And both of those cell types arise early in development in the part of the embryo called the ectoderm. Most neurons and glia found in the central nervous system are derived from neural stem cells, while most neurons and glia found in the peripheral nervous system are derived from neural crest cells. Now, we'll go into a lot more detail about what neural stem cells are and neural crest cells in other videos, when we cover development of the nervous system. Most types of both neurons and glia share some structural features of the way their cell is shaped. Most of them have a main part to their cell called the soma or the cell body that contains the nucleus and most of the organelles. Coming out of the soma, most of these cell types have processes, long, thin extensions that come out of the soma. And the processes of the different neural cells vary in number and in length, in thickness, and degree of branching, because some of them will be unbranched, and some of them will have processes that branch, sometimes a little and sometimes a lot. They will also vary a lot in the terminal structures at the end of their processes and the function of these structures and the processes. The function of neurons is to process and transmit information. And the function of glia is to support them in a variety of ways. There are many structural and functional types of both the neurons and the glia. And there are large numbers of these cells making up the nervous system. There are billions of neurons that form trillions of connections in the adult human nervous system. And there even more glia than there are neurons. In subsequent videos, we'll go over the most common glia, which are astrocytes, microglia, ependymal cells, oligodendrocytes, and Schwann cells. There are also less common glia, such as satellite cells and olfactory and sheathing cells. But we'll just go over the most common types here.