![]() ![]() Actually, gray matter may have that color ascribed to it because next to the white matter, it is just darker-hence, gray. Lipids can appear as white (“fatty”) material, much like the fat on a raw piece of chicken or beef. White matter is white because axons are insulated by a lipid-rich substance called myelin. It can be pinkish because of blood content, or even slightly tan, depending on how long the tissue has been preserved. The colors ascribed to these regions are what would be seen in “fresh,” or unstained, nervous tissue. ![]() Figure 16.2 demonstrates the appearance of these regions in the brain and spinal cord. These two regions within nervous system structures are often referred to as gray matter (the regions with many cell bodies and dendrites) or white matter (the regions with many axons). Looking at nervous tissue, there are regions that predominantly contain cell bodies and regions that are largely composed of just axons. Dendrites are responsible for receiving most of the input from other neurons. Another type of process that branches off from the soma is the dendrite. There is one important process that every neuron has called an axon, which is the fiber that connects a neuron with its target. Neurons are cells and therefore have a soma, or cell body, but they also have extensions of the cell each extension is generally referred to as a process. To describe the functional divisions of the nervous system, it is important to understand the structure of a neuron. The neuron is the more functionally important of the two, in terms of the communicative function of the nervous system. A glial cell is one of a variety of cells that provide a framework of tissue that supports the neurons and their activities. Neurons are important, but without glial support they would not be able to perform their function. Ongoing research pursues an expanded role that glial cells might play in signaling, but neurons are still considered the basis of this function. Play a supporting role for nervous tissue. Depending on different aspects of the nervous system, the dividing line between central and peripheral is not necessarily universal. The peripheral nervous system is so named because it is on the periphery-meaning beyond the brain and spinal cord. In actuality, there are some elements of the peripheral nervous system that are within the cranial or vertebral cavities. It is a bit of an oversimplification to say that the CNS is what is inside these two cavities and the peripheral nervous system is outside of them, but that is one way to start to think about it. The brain is contained within the cranial cavity of the skull, and the spinal cord is contained within the vertebral cavity of the vertebral column. The central nervous system (CNS) is the brain and spinal cord, and the peripheral nervous system (PNS) is everything else (see Figure 16.1). ![]() Anatomy (Structures) of the Nervous System The Central and Peripheral Nervous Systems The nervous system can be divided into two major regions: the central and peripheral nervous systems. ![]()
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