Remember that although autonomic neurons look generally rounded in outline, they are actually multipolar neurons with very fine dendritic processes, and they are visceral motor neurons, responsible for involuntary control of smooth and cardiac muscle. The outer connective tissue sheath surrounding the entire nerve is the epineurium. The connective tissue sheath surrounding each round bundle is the perineurium. Slide 12A Scanning electron micrograph of a cross-section of a peripheral nerve showing individual axons surrounded by myelin sheaths. The axons have undergone some shrinkage with specimen preparation and have receded from the surface of the section.
Myelinated axons are visible beneath the translucent perineurium.
A higher magnification of one bundle of peripheral nerve, showing cross-cuts of individual processes. The best ones show a darker axon in the center of the fiber, surrounded by a paler myelin sheath. Remember that some of these fibers are axons of motor neurons, whose cell bodies are in the anterior horn of the spinal cord, while other fibers are dendrites of the pseudounipolar sensory cells of the spinal ganglion. The dense sheath at the outer edge of the bundle here is perineurium. The lines of pink surrounding each process represent endoneurium.