STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Nerve fibre. Coloured transmission electron micrograph (TEM) of a section through a non-myelinated peripheral nerve fibre. Here several axons (green) can be seen surrounded by the cytoplasm of a Schwann cell (purple). Perineurial cells surround the whole nerve bundle. Non-myelinated nerve fibres lack the concentric myelin sheaths that surround other types of nerve, and which improve the conduction of nerve impulses. It is usually smaller nerves, such as those of the autonomic nervous system, that are not myelinated. Magnification: x3000 when printed 10 centimetres wide.
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