nt_08. Myelinated nerve fibers
(osmium impregnation)
1. Identify myelinated fibers and explore their structure:
- the myelin sheath is a layer of lipids that surrounds the axis cylinder (nerve cell axon of the neuron):
- when stained with osmium, the myelin sheath appears as a thick black ring around a pale axon;
- the myelin sheath itself is the inner portion of the Schwann cell, and the outermost layer that contains the nucleus and cytoplasm is the neurilemma (also called neurolemma, Schwann’s sheath);
- two adjacent segments of myelin on one axon are separated by the node of Ranvier, also known as a myelin-sheath gap (in this region the axon is not covered by myelin;
- external to the neurilemma is a basal lamina and then a thin sleeve of fibrous connective tissue.
2. Draw and point out:
- 1 - the axial cylinder,
- 2 - the myelin sheath,
- 3 - the node of Ranvier,
- 4 - the neurilemma,
- 5 - the basal lamina.
3. Define and write significant features of the specimen