Figure 1114

Diagram of an axon and its covering sheaths.

This diagram shows a longitudinal section of the axon and its relationships to the myelin, cytoplasm of the Schwann cell, and node of Ran-vier. Schwann cell cytoplasm is present at four locations. These are (1) the inner and (2) the outer cytoplasmic collar of the Schwann cell, (3) the nodes, and (4) the Schmidt-Lanterman clefts. Note that the cytoplasm throughout the Schwann cell is continuous; it is not a series of cytoplasmic islands as it appears in the diagram (see Fig. 11.15). The node of Ranvier is the site at which successive Schwann cells meet. The adjacent plasma membranes of the Schwann cells are not tightly apposed at the node, and extracellular fluid has free access to the neuronal plasma membrane. Also, the node is the site of depolarization of the neuronal plasma membrane during nerve impulse transmission. (Courtesy of Dr. Charles P. Leblond.)

inner collar of Schwann cell cytoplasm node of Ranvier nucleus of Schwann cell outer collar of Schwann of Schwann cell

Schmidt-Lanterman cleft collar of Schwann cell cytoplasm inner collar of Schwann cell cytoplasm inner collar of Schwann cell cytoplasm

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