03 CERVICAL VERTEBRAE
# 03 CERVICAL VERTEBRAE
Detailed notes
The cervical spine carries the head, transmits the spinal cord, and channels the vertebral arteries into the skull. For MRCS Part A you do not need to memorise every bony detail — you need to recognise the atypical vertebrae (C1, C2, C6, C7) on sight and know what structure lies at each level. Examiners lean heavily on these landmarks because they integrate anatomy with surface markings and surgical access.
There are seven cervical vertebrae. C3–C5 are "typical" and largely interchangeable: small kidney-shaped body, large triangular vertebral foramen (accommodating the cervical enlargement of the cord), short bifid spinous process, and a transverse foramen transmitting the vertebral artery, vein and sympathetic plexus. Two further features distinguish cervical from thoracic or lumbar vertebrae: uncinate processes on the superolateral body (forming the uncovertebral joints of Luschka, a common site of osteophyte formation causing cervical radiculopathy), and anteriorly tilted, bifid spinous processes that accommodate the ligamentum nuchae. The four atypical vertebrae are the ones that earn questions.
The atypical cervical vertebrae
C1, Atlas ➡ No body and no spinous process — just an anterior and posterior arch united by lateral masses. The atlas is essentially a bony ring that cradles the occipital condyles, allowing the "yes" nod at the atlanto-occipital joint. It has no intervertebral disc above or below in the usual sense — its body has migrated to fuse with C2 as the dens.
C2, Axis ➡ Long bifid spinous process plus the odontoid peg (dens) projecting upward from its body. The dens is held against the anterior arch of C1 by the transverse ligament of the atlas, forming a pivot that produces the "no" shake at the atlanto-axial joint. If this ligament ruptures (rheumatoid arthritis, Down syndrome, trauma), the dens can compress the spinal cord — an exam favourite.
C3 ➡ Typical small bifid spinous process. Lies at the level of the hyoid bone.
C4 ➡ Typical. Marks the superior border of the thyroid cartilage and the carotid bifurcation.
C6 ➡ Prominent carotid (Chassaignac's) tubercle on the anterior tubercle of the transverse process. Three high-yield facts cluster here:
- The vertebral artery enters the transverse foramen at C6 (it skips C7's foramen) and ascends through C5–C1 to enter the skull via the foramen magnum.
- The common carotid artery can be compressed against the carotid tubercle — useful for haemorrhage control and historically for diagnosing carotid pathology.
- The trachea, oesophagus and recurrent laryngeal nerve all begin at C6 (cricoid cartilage); this is also where the larynx ends and the pharynx becomes the oesophagus.
C7, Vertebra prominens ➡ Long, non-bifid spinous process — the most palpable vertebral landmark at the base of the neck. Its transverse foramen, when present, transmits only small accessory veins, not the vertebral artery.
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Vertebral levels — a high-yield summary
| Level | Anterior structure |
|---|---|
| C3 | Hyoid bone |
| C4 | Superior thyroid cartilage / carotid bifurcation |
| C5 | Mid thyroid cartilage |
| C6 | Cricoid cartilage; trachea, oesophagus and recurrent laryngeal nerve begin; vertebral artery enters transverse foramen |
| C7 | Vertebra prominens (posterior landmark) |
👩⚕️ A reliable exam shortcut: "C6 is where everything begins." Trachea, oesophagus, recurrent laryngeal nerve all start at C6, and the vertebral artery enters its bony tunnel here too. If a question gives you any of these, the answer is almost certainly C6.
👩⚕️ Do not confuse the carotid bifurcation (C4) with the carotid tubercle (C6). The bifurcation is the anatomical event; the tubercle is the bony landmark used to compress the artery lower down.
Why these levels matter clinically
- Cricothyroidotomy is performed through the cricothyroid membrane just above the cricoid (C6) — knowing the cricoid sits at C6 anchors the surface anatomy of emergency airway access.
- Central venous access and stellate ganglion blocks rely on the carotid tubercle at C6 as a palpable landmark. Damage to the stellate ganglion produces Horner's syndrome (ptosis, miosis, anhidrosis).
- Atlanto-axial subluxation in rheumatoid arthritis can cause myelopathy; pre-operative cervical spine films are mandatory before intubating these patients. The same risk applies in Down syndrome (ligamentous laxity) and Os odontoideum.
- Hangman's fracture is a bilateral pars interarticularis fracture of C2, classically from hyperextension; Jefferson's fracture is a burst fracture of the C1 ring from axial loading (diving into shallow water, helmet impact). Both are unstable and demand immobilisation.
- Vertebral artery dissection can complicate cervical manipulation or whiplash — the artery is tethered as it exits the C1 transverse foramen and bends sharply toward the foramen magnum, making it vulnerable to shear injury.
Spinal cord levels versus vertebral levels
A subtle but examinable point: the spinal cord segment does not correspond to the vertebral level in adults. In the cervical region the mismatch is small (cord segment ≈ one level above the vertebra), but it becomes important when interpreting imaging or planning surgery. The cervical enlargement (C4–T1) houses the lower motor neurones supplying the upper limb — this is why high cervical injuries spare the arms while mid-cervical injuries (C5–C7) cause the segmental motor patterns tested in MRCS.
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Test yourself
Which cervical vertebra is characterised by a long bifid spinous process?
- ((C1 (Atlas)::No spinous process — just anterior and posterior arches around the dens.))
- ((C2 (Axis)::☑️ Long bifid spinous process plus the odontoid peg (dens).))
- ((C6::Has the anterior carotid tubercle, not a bifid spine.))
- ((C7 (Vertebra prominens)::Long spinous process but non-bifid — most palpable posteriorly.))
The vertebral artery enters the foramen transversarium at which level?
- ((C4::Level of carotid bifurcation, not vertebral artery entry.))
- ((C5::Vertebral artery has already entered one level lower.))
- ((C6::☑️ Enters at C6, marked by the prominent carotid (Chassaignac's) tubercle.))
- ((C7::Transverse foramen of C7 transmits only small accessory veins, not the artery.))
👩⚕️ The vertebral artery skips C7 — a classic SBA trap.
At which vertebral level can the common carotid artery pulsation be compressed, and the trachea begin?
- ((C4::Level of carotid bifurcation, not tracheal start.))
- ((C5::Mid-thyroid cartilage — no major landmark begins here.))
- ((C6::☑️ Common carotid compressed against Chassaignac's tubercle; cricoid, trachea and oesophagus all begin.))
- ((T4/T5::Sternal angle — site of tracheal bifurcation, not its start.))
Which cervical vertebra is most prominently felt on the back of the neck?
- ((C5::Not typically palpable.))
- ((C6::Level of cricoid, palpable anteriorly but not the posterior prominence.))
- ((C7::☑️ Vertebra prominens — long, non-bifid spinous process, easily palpable.))
- ((T1::Sometimes palpable but C7 dominates the posterior landmark.))
Revision summary
- C1 Atlas ➡ ring with no body, no spinous process; atlanto-occipital "yes" nod.
- C2 Axis ➡ long bifid spinous + dens; atlanto-axial "no" shake; held by transverse ligament.
- C3 ➡ hyoid level.
- C4 ➡ superior thyroid cartilage; carotid bifurcation.
- C6 ➡ cricoid cartilage; carotid (Chassaignac's) tubercle; vertebral artery enters transverse foramen; trachea, oesophagus and recurrent laryngeal nerve all begin.
- C7 ➡ vertebra prominens; long non-bifid spinous process; transverse foramen does not transmit the vertebral artery.
- Fractures: Jefferson = C1 burst; Hangman's = C2 pars; atlanto-axial subluxation = RA / Down syndrome.