2.3.3: Glial Cells of the PNS — Read

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The satellite cell is recognized among the two distinct types of glial cells evident within the PNS. These cells inhabit sensory and autonomic ganglia, enveloping the neuron cell bodies therein. The nomenclature attributed to these cells corresponds to their morphological characteristics. Satellite cells serve a supportive role akin to the functions assumed by astrocytes within the CNS, except for establishing the BBB.

Schwann cell is another subtype of glial cell that provides myelin insulation to axons within the PNS. They contrast with oligodendrocytes in that each Schwann cell wraps a solitary axon segment, whereas oligodendrocytes extend processes that span multiple axon segments. Myelin, a lipid-dominant envelope, encircles the axon, engendering a myelin sheath that expedites the conduction of electrical impulses along the axon. The nucleus and cytoplasm of the Schwann cell remain positioned at the periphery of the myelin sheath (Figure 7). The extension of myelin sheaths can span from one to two millimeters, contingent upon axon diameter. Axon diameters range from 1 to 20 micrometers. The length of a myelin sheath can potentially be 100–1000 times greater than the diameter of the axon. Figures 7 and 8 illustrate the encompassing of a myelin sheath around an axon segment, although not according to scale.

Diagram of a unipolar neuron with labels. Features include a round cell body, a single axon, and satellite and Schwann cells surrounding the neuron. — Figure 7 | Glial Cells of the PNS | ⁹ This figure depicts the two types of glial cells found within the PNS, contributing to the structural and functional support of peripheral nerves. Schwann Cells are principal glial cells in the PNS responsible for myelinating axons. They form the myelin sheath around individual axons, aiding in the rapid transmission of nerve impulses. Satellite Cells surround and support cell bodies of neurons within the ganglia in the PNS.

Diagram showing neurons: the first neuron with labeled axon and dendrite, the second with labeled myelin, and the third illustrating nodes of Ranvier. All are cross-sectional views. — Figure 8 | The Process of Myelination by Schwann Cells | ¹⁰ This illustration captures the myelination process carried out by Schwann cells in the PNS. Schwann cells recognize and envelop individual axons in the PNS by wrapping around the axon multiple times, forming a myelin sheath consisting of numerous layers of lipid-rich membrane. As the Schwann cell continues to wrap around the axon, the layers of the myelin membrane compact, resulting in the formation of a myelin sheath that insulates the axon. Nodes of Ranvier are gaps in the myelin sheath where the axon is exposed.

During development, the glial cell displays a provisional or incomplete enclosure around the axon (Figure 8). The peripheries of this provisional wrapping incline towards convergence, with one extremity folding beneath the other. The inner perimeter enwraps the axon, configuring multiple strata, while the opposing border envelops the external surface, thus culminating in the comprehensive encapsulation of the axon. Schwann cells continuously monitor and maintain the myelin sheath throughout the life of the axon¹¹. Upon axonal transection, the proximal stub emits multiple regenerating sprouts. The sprout that successfully interfaces with an adjacent Schwann cell continues to elongate, eventually reinnervating the target cell.

This page titled 2.3.3: Glial Cells of the PNS was last modified on Sat, 22 Aug 2026 02:49:06 GMT and is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Chaya Gopalan (Consortium of Academic and Research Libraries in Illinois (CARLI)) .

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