Schwann cells

A peripheral nerve, cut in cross section, shows numerous axons of various sizes surrounded by myelin sheaths. The myelin sheath is produced by Schwann cells in the peripheral nervous system and consists of a series of myelin units, internodes, each produced by a single Schwann cell. Each internode is produced by the spiraling wrapping of Schwann cell membrane around the axon. The Schwann cell nucleus is located midway along the length of each internode and thus nuclei are not visible in each myelinated axon. An endoneurium surrounds each sheath. 1000x

A myelin sheath surrounds an individual axon and consists of myelin segments (internodes) arranged linearly along the axon. Each internode is produced by the spiral wrapping of the Schwann cell plasma membrane around the axon. The uniquely high lipid content of the myelin membrane insulates the axon and increases conduction velocity. The radial lines in the sheath are proteinaceous remnants of the plasma membrane. Endoneurium surrounds the Schwann cells.

A myelin sheath surrounds an individual axon and consists of myelin segments (internodes) arranged linearly along the axon. Each internode is produced by the spiral wrapping of the Schwann cell plasma membrane around the axon. The uniquely high lipid content of the myelin membrane insulates the axon and increases conduction velocity. The radial lines in the sheath are proteinaceous remnants of the plasma membrane. Endoneurium surrounds the Schwann cells.

A myelin sheath surrounds an individual axon and consists of myelin segments (internodes) arranged linearly along the axon. Each internode is produced by the spiral wrapping of the Schwann cell plasma membrane around the axon. The uniquely high lipid content of the myelin membrane insulates the axon and increases conduction velocity. The radial lines in the sheath are proteinaceous remnants of the plasma membrane. Endoneurium surrounds the Schwann cells.

The next image is similar to that outlined by the rectangle seen by electron microscopy.