12 Cranial Nerves: Origin & Conduction Map

Select a Cranial Nerve

Nerve Info

Live Readouts

Conduction velocity

— m/s

Time to target

— ms

Fiber path length

— cm

Quiz score

0 / 0

Playback speed 1.0×

How it works

Each of the 12 cranial nerve pairs emerges from a specific level of the brainstem (or forebrain, for CN I/II) and is classified by the fiber types it carries: purely sensory (afferent only), purely motor (efferent only), or mixed.

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

This simulator assigns each nerve a representative conduction velocity for its dominant fiber population and an approximate anatomical path length to its target, then computes t = d/v live. The travelling dots on the 3D nerve trace move 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 — highlights its true brainstem exit level and traces the signal.
Show all 12 — lights up every 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.

Sensory Motor Mixed

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