Which cranial nerve is the largest?

• A. First
• B. Fifth
• C. Seventh
• D. Ninth

Answer: (B)

The largest cranial nerve is determined by its size and mass at its root, not how long it runs or its number. The fifth cranial nerve, the trigeminal nerve, is the largest. It has a very substantial sensory root and the largest sensory ganglion (the trigeminal ganglion), plus a broad distribution across the face via its three divisions—ophthalmic, maxillary, and mandibular. That wide reach and heavy fiber content give it a greater cross-sectional size than the others. In contrast, the olfactory nerve is microscopic, the facial nerve is large but not the largest, and the glossopharyngeal nerve is smaller and less extensive. So the trigeminal nerve stands out as the largest in size among the cranial nerves.