Final answer:
Microtubules and neurofilaments provide tensile strength to the axon and dendrite of a neuron. The myelin sheath, made by glial cells, insulates the axon and appears dark in stained electron micrographs. Nodes of Ranvier are gaps in the myelin sheath crucial for rapid impulse conduction.
Step-by-step explanation:
The structures that extend into the axon and dendrite of a neuron to provide tensile strength are microtubules and neurofilaments. These structures are part of the neuron's cytoskeleton, providing support and shape to the neuron. The axon is insulated by the myelin sheath, produced by glial cells, which enhances the speed of electrical signal transmission along the axon. The myelin appears as a dark black color when stained in electron micrographs due to its lipid content. In myelinated axons, there are periodic gaps known as nodes of Ranvier, which are essential for the rapid conduction of nerve impulses.