# Cervical and Atypical Vertebrae > Cervical and atypical vertebrae for MBBS Anatomy: atlas, axis, vertebra prominens, carotid tubercle and vertebral artery course. - Canonical URL: https://prepelephant.com/topics/mbbs/anatomy/cervical-and-atypical-vertebrae - Exam / course: MBBS · Subject: Anatomy - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Cervical and Atypical Vertebrae", PrepElephant, https://prepelephant.com/topics/mbbs/anatomy/cervical-and-atypical-vertebrae ## Direct answer Turning the head to look over the shoulder happens mostly at one joint — the atlantoaxial — while nodding belongs to the atlanto-occipital joint; both sit at the top of a cervical column whose typical members (C3-C6) are recognised by a small body, a bifid spine, a large triangular canal and a foramen transversarium in each process carrying the vertebral artery. The atypical vertebrae carry the exam's weight: the atlas has no body and no spine, the axis carries the dens (the atlas's fused body) held against it by the transverse ligament, C6 sports the palpable carotid tubercle of Chassaignac, and C7 — the vertebra prominens — has the long, non-bifid spine felt at the neck's base. Two injuries bear the column's violence — the Jefferson burst and the hangman's fracture, both of the atlantoaxial complex. ## What you must remember - **Typical cervical (C3-C6):** small, wide body with uncinate processes; foramen transversarium in the transverse process with the anterior tubercle homologous to a rib; bifid spine ending in two tubercles for asymmetrical muscle pull. - **Atlas (C1):** no body, no spine — only a short anterior arch with its tubercle (for the longus colli), a posterior arch grooved by the vertebral artery above its root, and lateral masses with superior facets for the occipital condyles. - **Axis (C2):** the dens (odontoid process) is the atlas's body fused to the axis; the transverse ligament of the cruciform complex holds the dens against the anterior arch — its rupture in rheumatoid arthritis or Down syndrome endangers the cord. - **Axis injuries:** the Jefferson fracture bursts both anterior and posterior atlas rings under axial load (a fall or dive onto the head); the hangman's fracture breaks both C2 pars interarticularis, classically from hyperextension — judicial hanging traumatised exactly this. - **C6 and C7:** the carotid tubercle (Chassaignac) is the enlarged anterior tubercle of C6 against which the common carotid can be compressed; the vertebra prominens has the longest, usually non-bifid cervical spine. - **Vertebral artery course:** it enters the foramen transversarium of C6 and ascends through C6-C1 — the C7 foramen normally transmits only accessory veins, a one-mark fact asked repeatedly. - **Neighbouring levels:** the phrenic nerve (C3, C4, C5 keeps the diaphragm alive) and the brachial plexus (C5-T1) hang off this column, so cervical injuries are read by their root deficits. ## Two crashes, two vertebrae A diver strikes a shallow pool bottom with his head: an axial load drives the occipital condyles down onto the atlas ring, which bursts at its weakest points — the junctions of anterior and posterior arches with the lateral masses — the Jefferson fracture. Because the fragments splay outward and widen the canal, many survive neurologically intact unless the transverse ligament ruptures, converting a stable burst into an unstable disruption. Different mechanism, same column: a hyperextension injury, the chin snapping against a dashboard, shears both C2 pars interarticularis — the hangman's fracture — while the large canal at that level may again spare the cord. The clinical lesson for both is that the C1-C2 region tolerates surprising displacement, and the anatomical lesson is that the axis is the column's keystone: the dens, held by ligaments alone, is the weak link — in rheumatoid arthritis the eroded transverse ligament lets the atlas slide forward onto the cord. ## Where students slip Asked to list the atypical cervical vertebrae, candidates write C1 and C2 and stop; the exam expects C1, C2, C7 — and a good answer adds C6 for its carotid tubercle. The second slip is the vertebral artery: it enters at C6, not C7, and the examiner probes precisely because the C7 foramen exists yet carries only veins. Third, the dens is not "part of the axis" embryologically — it is the atlas's body, separated and fused to the axis, which is why odontoid hypoplasia and os odontoideum are atlantoaxial problems. Quoting that embryology converts a list answer into a viva-winning one. ## Frequently asked questions ### Which cervical vertebrae are atypical and why? The atlas (no body or spine), the axis (bears the dens) and C7 (long, non-bifid spine — the vertebra prominens); C6 is often added for its carotid tubercle of Chassaignac. Each atypical feature has a functional or clinical correlate. ### What is a Jefferson fracture? A burst fracture of the atlas ring under axial load, breaking the arches at the junctions with the lateral masses. Because the fragments splay outward, cord injury is often spared unless the transverse ligament ruptures. ### What is a hangman's fracture? Bilateral fracture of the pars interarticularis of the axis from hyperextension, separating the C2 body from its posterior elements. Despite its name, most modern cases survive without permanent cord damage. ### At which level does the vertebral artery enter the foramen transversarium? At C6, ascending through the foramina of C6 to C1 before turning medially on the atlas's posterior arch. The C7 foramen usually transmits only an accessory vertebral vein. ### What is the carotid tubercle and its use? The enlarged anterior tubercle of the C6 transverse process, palpable in the neck, against which the common carotid artery can be compressed to control bleeding — Chassaignac's tubercle.