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Semicircular canal anatomy, in 3D
Six canals, three planes, one head. Once you can picture how the canals sit in the skull, vestibular physiology and BPPV become far easier to reason about.
- Name the three canals and describe how each one is angled.
- Find the ampullae, cupulae and common crus.
- Name the three canal pairs and which nerve supplies each canal.
Three canals, at right angles
Each inner ear has an anterior (also called superior), a posterior and a lateral (also called horizontal) canal. They sit roughly at right angles to each other, so together they can sense rotation in any direction.
Lateral
Tilted up at the front by about 30° from the horizontal when you stand upright. Tipping the head down about 30° brings it level.
Anterior
Vertical, at about 45° to the midline, facing forwards and outwards.
Posterior
Vertical, at about 45° to the midline, facing backwards and outwards. It’s the lowest canal when lying down.
The three pairs
Because of these angles, each canal shares a plane with one canal on the other side: the two lateral canals, left anterior with right posterior (LARP), and right anterior with left posterior (RALP). A head movement in a pair’s plane excites one canal and inhibits the other.
Inside the swelling: ampulla and cupula
Each canal widens at one end into an ampulla. Across it sits the crista, a ridge of hair cells, capped by the cupula: a gelatinous sail that seals the canal. The cupula has about the same density as endolymph, so gravity alone doesn’t move it; only rotation does. In BPPV, loose otoconia break that rule.
The non-ampullated ends of the anterior and posterior canals join to form the common crus. The lateral canal opens into the utricle on its own.
Nerve supply, and why it matters
The anterior and lateral ampullae sit close together at the front and are supplied by the superior vestibular nerve. The posterior ampulla, lower down, is supplied by the inferior vestibular nerve. Vestibular neuritis usually affects the superior division, so it tends to spare the posterior canal. That’s why posterior canal BPPV can follow it.
Try it with your model
- Find the six ampullae: each one carries a + or −.
- Lay a pencil along the left anterior canal, then find the parallel canal on the right. It’s the right posterior (LARP).
- Tip the head down 30° and check the lateral canals come level.
- Lay the model flat on its back: the posterior canals now form the lowest point, where loose particles collect.
- Three canals per ear, at roughly right angles: anterior, posterior and lateral.
- Coplanar pairs: lateral–lateral, LARP and RALP.
- Ampulla → crista → cupula. The cupula senses rotation, not gravity.
- Superior vestibular nerve: anterior and lateral canals. Inferior vestibular nerve: posterior canal.
Check yourself
Which canal lies in the same plane as the left anterior canal?
The right posterior canal. Together they form the LARP pair.
Which nerve supplies the posterior canal?
The inferior vestibular nerve. The anterior and lateral canals are supplied by the superior vestibular nerve.
Why is the head raised 30° when lying down for caloric testing?
Lying back with the head 30° up turns the lateral canal vertical, which gives the strongest temperature-driven flow in that canal.
For education only, not medical advice. Reviewed by a Consultant Neurologist and Neuro‑Otologist.