Classification of Neuroglia

Neuroglia (glial cells) were once thought to be mere bystanders to neural function, providing scaffolding and controlling the sites at which neurons contact one another (figs. 10.8 and 10.9). These important cells have additional functions. In the embryo, neuroglia guide neurons to their positions and may stimulate them to specialize. Neuroglia also produce the growth factors that nourish neurons and remove ions and neurotransmitters that accumulate between neurons, enabling them to continue transmitting information. In cell culture experiments, certain types of neuroglia (astrocytes) signal neurons to form and maintain synapses.

Schwann cells are the neuroglia of the peripheral nervous system. The central nervous system contains the following types of neuroglia:

1. Astrocytes. As their name implies, astrocytes are star-shaped cells. They are commonly found between neurons and blood vessels, where they provide support and hold structures together by means of abundant cellular processes. Astrocytes aid metabolism of certain substances, such as

Capillary

(b) Oligodendrocyte

Capillary

(b) Oligodendrocyte

Ependymal Cell Scanning Electron

Fluid-filled ii "jf cavity of the brain or spinal cord

(a) Microglial cell

Figure 10.8

Types of neuroglial cells in the central nervous system include (a) microglial cell, (b) oligodendrocyte, (c) astrocyte, and (d) ependymal cell.

Fluid-filled ii "jf cavity of the brain or spinal cord

(a) Microglial cell

Figure 10.8

Types of neuroglial cells in the central nervous system include (a) microglial cell, (b) oligodendrocyte, (c) astrocyte, and (d) ependymal cell.

Neuron cell body

Neuroglial cells

Figure

A scanning electron micrograph of a neuron cell body and some of the neuroglial cells associated with it (1,000x).

(Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy, by R. G. Kessel and R. H. Kardon, © 1979 W. H. Freeman and Company.)

glucose, and they may help regulate the concentrations of important ions, such as potassium ions, within the interstitial space of nervous tissue. Astrocytes also respond to injury of brain tissue and form a special type of scar tissue, which fills spaces and closes gaps in the CNS. These multifunctional cells may also have a nutritive function, regulating movement of substances from blood vessels to neurons and bathing nearby neurons in growth factors. Astrocytes also play an important role in the blood-brain barrier, which restricts movement of substances between the blood and the CNS (see Clinical Application 3.2, p. 73). Gap junctions link astrocytes to one another, forming protein-lined channels through which calcium ions travel, possibly stimulating neurons.

2. Oligodendrocytes. Oligodendrocytes resemble astrocytes but are smaller and have fewer processes. They commonly occur in rows along myelinated

Structure Human Neuroglia

Neuron cell body

Neuroglial cells

Figure

Shier-Butler-Lewis: I III. Integration and I 10. Nervous System I: I I © The McGraw-Hill

Human Anatomy and Coordination Basic Structure and Companies, 2001

Physiology, Ninth Edition Function

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