National Board of Chiropractic Examiners (NBCE) Practice Test

What is the outer collagenous layer surrounding peripheral nerves known as?

1. Epineurium

2. Perineurium

3. Endoneurium

4. Neurilemma

The correct answer is: Epineurium

The outer collagenous layer surrounding peripheral nerves is known as the epineurium. This structure serves several important functions. It provides a protective layer for the nerve, helping to insulate it from surrounding tissues and providing structural support. The epineurium also contains blood vessels that supply the nerve, allowing for adequate nourishment and waste removal. In contrast, the perineurium is the layer that surrounds individual fascicles (bundles of nerve fibers) within a nerve, providing a barrier that helps maintain the internal environment of the nerve. The endoneurium is the delicate layer that surrounds each individual nerve fiber or axon, offering additional support and protection at a more granular level. Neurilemma refers specifically to the outermost layer of the myelin sheath formed by Schwann cells around individual axons, but it does not encompass the entire nerve structure like the epineurium does. Understanding these different layers and their respective roles is crucial in comprehending the anatomy of peripheral nerves and their protective mechanisms.