2D companion to the 3D cranial-nerve map: the same anatomy and physiology, laid out as a flat schematic of the brainstem with each nerve's exit point drawn at its true rostro-caudal level (forebrain/midbrain/pons/medulla), fanned left/right purely for label clarity — in the body every pair is bilateral.
Signal speed along a nerve is set by axon diameter and myelination, following the classic Erlanger–Gasser fiber classes and Hursh's empirical rule for large myelinated axons:
v ≈ 6 × d (Hursh's approximation, d = axon diameter in µm, v in m/s)
Aα / Aβ (thick, myelinated): 70–120 m/s → limb & extraocular motor axons
Aδ (thin, myelinated): 5–30 m/s → fast pain, touch
B (preganglionic autonomic): 3–15 m/s → e.g. vagal efferents
C (unmyelinated): 0.5–2 m/s → olfactory receptor axons, slow pain
conduction time t = path length ÷ conduction velocity
Each nerve is assigned a representative conduction velocity for its dominant fiber population and an approximate anatomical path length to its target, then t = d/v is computed live. The travelling dots move along the curve at that same relative speed (scaled by the Playback speed slider for visibility) — the Optic and Vestibulocochlear nerves are fast, thick, heavily myelinated tracts; the Olfactory nerve's unmyelinated receptor axons and the Vagus's long, largely unmyelinated visceral fibers are dramatically slower.
- Click a nerve number (or its endpoint on the diagram) — highlights its true brainstem exit level and traces the signal.
- Filter by type — dims every nerve except sensory / motor / mixed, in both browse and "Show all" modes.
- Show all 12 — lights up every filtered nerve at once, color-coded by type (blue = sensory, red = motor, purple = mixed).
- Quiz mode — a random nerve's path is traced with its label hidden; pick the matching numeral from the answer grid.