Cervical vertebrae: anatomy of the seven neck bones from the atlas to C7

The cervical spine is made of seven vertebrae, C1 to C7. C1 is called the atlas and C2 the axis. Below the neck come the twelve thoracic (T1 to T12) and five lumbar (L1 to L5) vertebrae, then the sacrum and coccyx. (TeachMeAnatomy: The Cervical Spine.)

Cervical vertebrae have the smallest bodies in the spine, because they carry the least weight. Seen from the side, the neck curves forwards (a lordosis). This cervical curve is a secondary curve: it appears after birth, when a baby starts to hold its head upright. (OpenStax Anatomy and Physiology 2e, 7.3: The Vertebral Column.)

Anatomists split the seven into typical and atypical vertebrae. C3 to C6 share the same typical pattern. C1 and C2 are very different, and C7, although it looks much like C3 to C6, is usually counted as atypical too. (Radiopaedia: Typical cervical vertebrae.)

The 3D model above highlights C1 to C7 together with the vertebral arteries that climb through them. It is built from BodyParts3D, an adult male data set, and does not include the ligaments of the neck, which are described below.

A typical cervical vertebra, such as C4 or C5, has a small oval body and a relatively wide vertebral arch around a large vertebral foramen. The vertebral foramen is triangular. Its spinous process is relatively long, points downwards and is usually bifid (split into two at the tip). (Radiopaedia: Typical cervical vertebrae.)

The upper surface of each body is raised at its sides into small lips called uncinate processes. Each lip meets a bevelled area on the vertebra above, forming the uncovertebral joints. Because of this, the front of each intervertebral foramen is bordered by both the vertebra above and the one below. (Radiopaedia: Typical cervical vertebrae.)

Each transverse process has an anterior tubercle, a posterior tubercle and, between them, the transverse foramen (foramen transversarium). Behind the pedicles, the superior and inferior articular processes stack up as a column of bone (the articular pillar); the upper facets face up and back and the lower facets face down and forwards. (Radiopaedia: Typical cervical vertebrae.)

The anterior tubercle of C6 is large and is called the carotid (Chassaignac) tubercle. It separates the common carotid artery from the vertebral artery and is used as a landmark for nerve blocks of the brachial and cervical plexuses. (Radiopaedia: Carotid tubercle.)

Each cervical transverse process contains a transverse foramen (foramen transversarium). These foramina carry the vertebral artery, the vertebral vein and sympathetic nerve fibres. The vertebral arteries climb through these holes to supply the brain. (TeachMeAnatomy: The Cervical Spine.)

The vertebral artery usually enters the transverse foramen of C6 and climbs through C6 to C1. The transverse foramina of C7 are small and normally do not carry the artery, though they can carry vertebral veins, and occasionally the artery enters at C7. (Radiopaedia: C7 vertebra.)

At the top, behind each lateral mass of the atlas, the vertebral artery and the C1 spinal nerve lie in a groove on the upper surface of the posterior arch before the artery turns into the skull through the foramen magnum. (Radiopaedia: Atlas (C1).)

The atlas (C1) has no body and no spinous process. It is a ring of bone made of two lateral masses joined by a short anterior arch and a longer posterior arch. The posterior arch makes up about three-fifths of the ring. (Radiopaedia: Atlas (C1).)

On top of each lateral mass is a kidney-shaped, concave superior articular facet that cradles an occipital condyle of the skull. Under each lateral mass is a round inferior facet that sits on the axis. The anterior arch has a small anterior tubercle at the front and a facet at the back for the dens of C2. (Radiopaedia: Atlas (C1).)

The posterior tubercle at the back of the posterior arch is a rudimentary spinous process. The transverse processes of the atlas are wide, and each contains a transverse foramen for the vertebral artery. (Radiopaedia: Atlas (C1).)

The atlas ossifies from three centres: one for the anterior arch and one for each lateral mass. The lateral mass centres appear around the 7th week of fetal life and spread into the posterior arch, which fuses at about 3 to 4 years. The anterior centre joins the lateral masses at about 6 to 8 years. (Radiopaedia: Atlas (C1).)

The axis (C2) is the second cervical vertebra. Its defining feature is the dens (odontoid process), a tooth-like peg that projects upwards from the body. Embryologically, the dens is the body of C1 that has become attached to C2. (Radiopaedia: Axis (C2).)

The dens fits against the back of the anterior arch of the atlas and is held there by the transverse ligament of the atlas. The head and atlas rotate together around it. The axis also has large superior articular facets, transverse foramina, a thick lamina and a large, usually bifid spinous process. (Radiopaedia: Axis (C2).)

Two alar ligaments run from the sides of the dens to the margins of the foramen magnum and limit excessive rotation. The apical ligament joins the tip of the dens to the front of the foramen magnum. (Kenhub: Cervical spine.)

The dens forms from its own ossification centres, which fuse with each other before birth. The dens usually fuses to the body of C2 by about 3 to 6 years, and a faint line from this junction often stays visible on adult scans. A separate small bone at the tip (os odontoideum) is a recognised variant. (Radiopaedia: Axis (C2).)

C7 is called the vertebra prominens because its long spinous process is easy to feel through the skin at the base of the neck. Unlike C3 to C6, its spinous process is not bifid but ends in a rounded tubercle. (Radiopaedia: C7 vertebra.)

C7 has the longest spinous process of the cervical vertebrae, and it is easiest to feel when the head is bent forwards. (Kenhub: Cervical spine.)

A cervical rib is an extra rib that grows from C7. It is found in about 0.5% of people, is usually on both sides and is more common in females. Most cause no symptoms, but some compress the brachial plexus or subclavian vessels (thoracic outlet syndrome). (Radiopaedia: Cervical rib.)

The atlanto-occipital joint (Latin articulatio atlantooccipitalis, often called the AO joint or C0-C1) is a pair of condyloid synovial joints. On each side, the convex occipital condyle sits in the concave superior facet of the atlas. (Radiopaedia: Atlanto-occipital joint.)

The AO joint is the joint of nodding. It allows about 25 degrees of flexion and extension and only about 5 degrees of rotation. Its capsule is supplied by the C1 nerve. (Radiopaedia: Atlanto-occipital joint.)

The joint is closed in by membranes. The anterior atlanto-occipital membrane is the upward continuation of the anterior longitudinal ligament. The posterior atlanto-occipital membrane is the upward continuation of the ligamentum flavum. The tectorial membrane, the upward continuation of the posterior longitudinal ligament, runs from the axis to the front of the foramen magnum. (Radiopaedia: Atlanto-occipital joint.)

The atlantoaxial (AA, C1-C2) articulation is a set of three synovial joints. The median atlantoaxial joint is a pivot joint between the dens, the anterior arch of the atlas and the transverse ligament. The two lateral atlantoaxial joints are plane joints between the lateral masses of C1 and C2. (Radiopaedia: Atlanto-axial joint.)

These joints are built for rotation, the movement you use to shake your head for 'no'. Radiopaedia gives about 30 degrees of rotation at C1-C2, with 10 to 15 degrees of flexion and extension and very little side bending. Other references give larger rotation figures; whichever figure is used, the atlantoaxial joints provide a large share, often quoted as about half, of all the neck's rotation. (Radiopaedia: Atlanto-axial joint.)

The joint capsules are thin, so ligaments provide most of the stability. The strongest is the transverse band of the cruciform ligament, which holds the dens against the atlas. Together with its upper and lower longitudinal bands it forms a cross, hence cruciform. (Radiopaedia: Atlanto-axial joint.)

If the transverse ligament is lax, the dens can move backwards and compress the spinal cord (atlantoaxial subluxation). Kenhub notes the link with Down syndrome and rheumatoid arthritis, and that MRI is the best way to see the ligament. (Kenhub: Cervical spine.)

There are eight pairs of cervical spinal nerves but only seven cervical vertebrae. Nerves C1 to C7 leave above the vertebra of the same number. C8 has no vertebra of its own, so it leaves below C7, through the foramen between C7 and T1. (Radiopaedia: C7 vertebra.)

As a result, C7 has a spinal nerve exiting both above it (C7) and below it (C8). (TeachMeAnatomy: The Cervical Spine.)

A Jefferson fracture is a break through the arches of the atlas, caused by a vertical load through the head while the neck is extended. The transverse ligament may tear. Cord damage is less likely at C1 because the vertebral canal there is wide. (TeachMeAnatomy: The Cervical Spine.)

A hangman's fracture is a fracture through the pars interarticularis of C2 caused by violent hyperextension and distraction. Fractures of the dens make up about 40% of C2 fractures; they are often unstable, and the upper fragment has a poor blood supply, so it may fail to heal. (TeachMeAnatomy: The Cervical Spine.)

In whiplash, sudden hyperextension of the neck can strain the anterior longitudinal ligament. Severe injuries can fracture or dislocate vertebrae, and C6/C7 is the most common level for subluxation. (TeachMeAnatomy: The Cervical Spine.)

Disc herniation in the neck is most common at C5/C6 and C6/C7, where it can press on nerve roots and cause pain in the neck, shoulder and upper limb. In the lower back the commonest levels are L4/L5 and L5/S1. (OpenStax Anatomy and Physiology 2e, 7.3: The Vertebral Column.)

Atlas

The first cervical vertebra (C1), a ring-shaped bone that supports the skull.

Axis

The second cervical vertebra (C2), distinguished by a tooth-like upward projection called the dens.

Fifth cervical vertebra

The fifth of the seven cervical (neck) vertebrae, labelled C5.

Fourth cervical vertebra

The fourth of the seven cervical (neck) vertebrae, labelled C4.

Seventh cervical vertebra

The seventh of the seven cervical (neck) vertebrae, labelled C7.

Sixth cervical vertebra

The sixth of the seven cervical (neck) vertebrae, labelled C6.

Third cervical vertebra

The third of the seven cervical (neck) vertebrae, labelled C3.

Vertebral artery

A branch of the subclavian artery supplying the brain and spinal cord.