Cranial Nerves & Skull Base | Foramina & Lesions | USMLE Step 1

Trace cranial nerves through the skull base and connect each canal, fissure, and foramen to a pattern of lost function. This USMLE Step 1 anatomy lesson covers the cribriform plate, optic canal, superior orbital fissure, trigeminal exits, internal acoustic meatus, jugular foramen, hypoglossal canal, and foramen magnum. Compare CN I–XII routes, ocular-motor versus sensory deficits, facial nerve branches, and spinal accessory entry versus exit. Use combined deficits to reason about lesion location while keeping peripheral patterns and anatomical variation in view. Reviewed seven-page companion chapter: https://usmlefox.com/lesson/V065 Chapters: 00:00 Introduction: cranial nerve corridors 00:17 Skull-base orientation 00:27 CN I and the cribriform plate 01:07 CN II and the optic canal 01:28 Superior orbital fissure 02:47 V1, V2 and V3 exits 03:21 Rotundum and ovale lesions 04:23 Spinosum and the meningeal artery 04:42 Internal acoustic meatus: VII and VIII 05:44 Facial nerve course and branches 06:48 Jugular foramen: IX, X and XI 07:47 Spinal accessory entry and exit 08:18 Hypoglossal canal and tongue weakness 09:01 Foramen magnum 09:21 Compare corridors and localize lesions Figure credits and source versions: OpenStax / Rice University, Anatomy and Physiology publisher figures, pinned publisher commit c5eaf900c0d13ae7a6a3d928b631917663f2713b (December 4, 2025), CC BY 4.0: https://creativecommons.org/licenses/... . Sphenoid Bone: https://github.com/openstax/osbooks-a... Cranial Fossae: https://github.com/openstax/osbooks-a... The Olfactory System: https://github.com/openstax/osbooks-a... External and Internal Views of Base of Skull: https://github.com/openstax/osbooks-a... Source-preserving panel and regional crops, proportional resizing, and separate teaching highlights/labels. Only the complete Olfactory System illustration panel (b) is used; the separately credited third-party micrograph is excluded. No endorsement is implied. Thumbnail: channel-style graphic adapted from the credited OpenStax superior skull-base illustration; project-authorized FOX branding. USMLE FOX is independent and is not affiliated with USMLE or NBME. Educational exam-preparation material; not personal medical advice. #USMLE #Step1 #CranialNerves