Cervical spine

Typical cervical vertebrae: C3-C6

The lower five cervical vertebrae are made up of the following structures:

• Vertebral body: Is small compared to the vertebral bodies in the rest of the spinal column owing to the fact they bear less weight than vertebrae further down the spine. Laterally, the vertebral bodies project slightly upwards creating the uncinate processes. These processes articulate with the bodies of the vertebra superior to them producing uncovertebral joints.
• Transverse processes (TVP): A typical feature of most vertebrae in the spinal column; these project laterally with one on each side. In the cervical spine, the transverse processes are unique due to the presence of the foramen transversarium or transverse foramen. Within these foramen, or holes, of C1-C6, run one of the two major arterial supplies to the brain, the vertebral arteries, the other being the internal carotid arteries. Accompanying the arteries are the vertebral veins. Additionally, the transverse processes of the vertebrae in the cervical spine are grooved for passage of spinal nerves. This groove divides the transverse process such that most laterally, each process has an anterior and posterior tubercle, for the attachment of muscles.
• Spinous process (SP): Project posteriorly and may be palpated in some cases since they lie beneath the skin on the back. The spinous processes of C3-C5 tend to be short and bifid, meaning that they divide into two parts posteriorly, with the spinous process of C6 being slightly longer but still bifid.

• Vertebral foramen: Is the bony canal in which the spinal cord runs. It is triangular in shape and comparatively large to accommodate the expansion of the cervical component of the spinal cord that provides all innervation to the upper limb. A similar enlargement is seen in the lumbar spinal cord to accommodate innervation of the lower limb. The vertebral foramen is made up of the posterior aspect of the vertebral body and the vertebral arch.
• Vertebral arch: Refers to the posterolateral bony components of the vertebral foramen. Extending posteriorly from each side of the vertebral body is a pedicle that runs between the body and the transverse process. The two lamina (one on each side) extend from the transverse processes to meet posteriorly at the spinous process.
• Articular processes (4): These are located immediately posterior to the transverse process and its foramen transversarium. There are two superior and two inferior processes. Each process has a smooth surface known as an articular facet. The two superior facets will articulate with the two inferior facets of the vertebra above, creating the zygapophyseal (or facet) joints. They may be referred to as joints of the vertebral arch since the processes themselves form on the lateral bony components of the arch. When the vertebrae are stacked one on top of the other, the vertebral arch, articular processes, and zygapophyseal joints of adjacent vertebrae create a passageway for spinal nerves known as the intervertebral foramen. The intervertebral foramen allows the spinal nerves at each vertebral level to exit the vertebral canal. Finally, the almost horizontal orientation of the articular facets in the cervical spine is, in part, responsible for giving the cervical spine the greatest variety and range of movement.

Test your knowledge of the cervical spine with this quiz.

Atypical cervical vertebrae: The atlas (C1), axis (C2) and C7

The first two cervical vertebrae are specialized vertebrae adapted to allow movement of the head and to accommodate articulation with the cranium, or skull.

Atlas (C1)

Unlike other vertebrae, the atlas does not have a spinous process or a body. When seen from above, the atlas is really a ring shape that thickens laterally to produce the lateral masses, which are joined by anterior and posterior arches. The anterior arch has three features to note:

• an anterior tubercle on the anterior surface
• a facet for the dens of the axis on the posterior surface
• and on either side of the facet, a tubercle for the transverse ligament that holds the dens in place

The posterior arch, instead of a spinous process, has a posterior protrusion known as the posterior tubercle. In addition, grooves for the vertebral arteries lay just posterior to the superior articular facets located on the lateral masses.

On the superior and inferior surfaces of the lateral masses are facets for articulations with other bones. Superiorly, the facets articulate with the occipital condyles of the occipital bone of the skull, and form the atlanto-occipital joints. Inferiorly, the facets articulate with the axis, forming the lateral atlanto-axial joints. Protruding laterally from the lateral masses are the transverse processes of the atlas that again feature the foramen transversarium.

Axis (C2)

The axis is more similar to the rest of the cervical spine vertebrae than the atlas but it does have an incredibly unique feature; the dens, or odontoid process. Often characterized as tooth-like or peg-like, this process is larger and longer than most other anatomical processes and extends from the body of C2. The dens and the spinal cord are encircled by the atlas. The dens makes an articulation with the posterior surface of the anterior arch of the atlas (the median atlantoaxial joint) and is held in place by the transverse ligament. The dens, and its articulation with the atlas, acts as a pivot around which rotation of the head can occur. The transverse ligament runs posterior to the dens (and anterior to the spinal cord), forming the posterior wall of the joint

On the posterior aspect of the dens are two facets for attachment of the alar ligaments. These ligaments connect the dens to the medial aspect of each occipital condyle and help restrict excessive rotation of the head.

Note: the atlanto-occipital joints allow for nodding, flexion/extension, or ‘yes’ motions of the head. The articulations between the atlas and axis (the two lateral atlantoaxial joints and the median atlantoaxial joint between the dens and the atlas) allow for rotation of the head or ‘no’ motions.

C7

C7 Is atypical for three reasons. The first is that the spinous process of C7 is the longest and can be easily palpated when the head is flexed forward as it is quite prominent in this position. In addition, the spinous process is not bifid. Finally, the foramen transversarium is quite small compared to the size of the transverse process and does not contain the vertebral arteries, just vertebral veins.

Ligaments that continue from below C7 (from anterior to posterior)

• Anterior longitudinal ligament (ALL): Attaches to and covers the anterior and lateral aspects of the vertebral bodies and intervertebral discs. This ligament extends from the anterior surface of the sacrum to C2. From C2 to C1 it is known as the anterior atlantoaxial membrane, and from C1 to the anterior aspect of the foramen magnum as the anterior atlanto-occipital membrane. These are the only spinal ligaments that limit hyperextension of the vertebral column.
• Posterior longitudinal ligament (PLL): Is a much narrower ligament that runs along the posterior aspect of the vertebral bodies, or alternatively, along the anterior aspect of the vertebral canal (the canal is made up of all of the vertebral foramen stacked on top of one another). It extends from the sacrum to C2. From C2, the PLL strengthens and becomes known as the tectorial membrane. It then passes through the foramen magnum to attach to the floor of the cranial cavity. Functionally, it weakly resists hyperflexion of the vertebral column, and helps prevent posterior herniations of the nucleus pulposus. Note: The PLL does not help prevent posterolateral herniations as it is absent in this region.

• Ligamentum flavum (pl. flava): Runs between the lamina of adjacent vertebrae. Because of its location, along with limiting hyperflexion, these ligamentous sections help enclose the posterior aspect of the vertebral canal. They also assist in straightening the spinal column after flexion. As with the ALL, the ligamentum flava continues from C2 and C1 as the posterior atlanto-axial and atlanto-occipital membranes. These membranes limit excessive motion at the atlanto-occipital joints.   
• Intertransverse ligament: Runs between the transverse processes of adjacent vertebrae.
• Interspinous ligament: Is a weak ligament that runs between the spinous processes of adjacent vertebrae.
• Nuchal ligament: Is a continuation of the supraspinous ligament in the cervical spine (C7 and above). Like the supraspinous ligament in the rest of the vertebral column, it runs along the tips of the spinous processes and is quite strong. It differs however in the cervical region, by extending posteriorly away from the spinous processes. This accommodates for muscular attachment, along with resisting hyperflexion.

Ligaments unique to the cervical spine

• Alar ligament: Runs from the posterior aspect of the dens of C2 to the lateral margins of the foramen magnum.
• Apical ligament: Connects the tip or apex of the dens of C2 to the anterior aspect of the foramen magnum.
• Transverse ligament: Holds the dens against the posterior aspect of the anterior arch of C1. Arising from this ligament are superior and inferior longitudinal ligamentous bands that attach the dens to the occipital bone and to the body of C2. In combination, the transverse ligament and the bands are known as the cruciate ligament.

Cervical plexus

Arises from the anterior rami of the spinal nerves associated with C1-C4 (some texts include the C5 nerve root). This plexus lies deep to the sternocleidomastoid (SCM) muscle and anteromedial to the levator scapulae and middle scalene muscles. The branches of the cervical plexus can be categorized as either muscular or cutaneous.

Muscular branches

• Phrenic nerve (C3-5): supplies the diaphragm.
• Ansa cervicalis (C1-3): supplies the infrahyoid muscles.
• Suboccipital Nerve (C1): supplies the suboccipital muscles.
• Nerves roots of C1-C3: supply prevertebral muscles.

The cervical plexus also contributes branches to these nerves:

• Dorsal scapular (C4,5): supplies the rhomboid major and minor, and levator scapulae muscles.
• Long thoracic (C5-7): supplies the serratus anterior muscle.

Cutaneous branches

• Lesser occipital (C2): skin of the neck and scalp.
• Great auricular (C2,3): skin surrounding the ear.
• Transverse cervical (C2,3): skin over the anterior cervical region.
• Supraclavicular (C3,4): skin over the clavicle and shoulder.

Brachial Plexus

It arises from the anterior rami of the spinal nerves associated with C5-T1 where the nerve roots appear between the anterior and middle scalene muscles. The nerve roots quickly combine to form nerve trunks: nerve roots C5 and C6 form the upper trunk, C7 the middle trunk, and C8 and T1 the lower trunk. Each trunk divides into an anterior and posterior division, which then combine to form three cords, the lateral, medial, and posterior cords. The cords then combine to form the five major nerves that supply the majority of the upper limb.

• Musculocutaneous (C5-7): Supplies muscles of the anterior compartment of the arm, and the skin of lateral forearm.
• Median (C5-8, T1): Supplies the majority of the muscles in the anterior compartment of the forearm, and the skin of the lateral 3 and a half fingers (mostly palmar aspect) and palm.
• Ulnar (C8, T1): Supplies the majority of the intrinsic muscles of the hand, and the skin of the medial 1 and a half fingers and hand (palmar and dorsal aspects).
• Radial (C5-8, T1): Supplies all muscles in the posterior compartments of the arm and forearm, and the skin of lateral 3 and a half fingers (dorsal aspect).
• Axillary (C5,6): Supplies the deltoid and teres minor muscles, and the skin over the deltoid.

Also arising from the brachial plexus are a number of minor nerves. In addition to the dorsal scapular and long thoracic nerves mentioned previously, these minor nerves are the:

• Nerve to subclavius (C5,6): Supplies the subclavius muscle.
• Suprascapular (C5,6): Supplies two of the rotator cuff muscles (the supraspinatus and infraspinatus).
• Lateral pectoral (C5-7): Supplies the pectoralis major muscle.
• Medial pectoral (C8, T1): Supplies the pectoralis major and pectoralis minor muscles.
• Medial cutaneous nerves of the arm and forearm (C8, T1): Skin of the medial aspect of the arm and forearm.
• Thoracodorsal (C6-8): Supplies the latissimus dorsi muscle.
• Upper and lower subscapular (C5,6): Together they supply one of the rotator cuff muscles, the subscapularis muscle. The lower subscapular nerve alone supplies the teres major and teres minor muscles.

Anterior neck muscles (flex head, flex neck, elevate ribs 1 and 2)

• Rectus capitis anterior: Origin - TVP of C1.
• Rectus capitis lateralis: Origin - TVP of C1.
• Longus capitis: Origin - anterior tubercles of TVPs of C3-C6.
• Longus colli: Part of origin - bodies of C5-C7, TVPs of C3-C5, Insertion - anterior tubercle of TVP of C1, bodies of C2-C5, TVPs of C5-C6.
• Anterior scalene: Origin - anterior tubercles of TVPs of C3-C6.
• Middle scalene: Origin - TVPs of C1/C2 -> C7 (specifically posterior tubercles of TVPs in C3-C7).
• Posterior scalene: Origin - posterior tubercles of TVPs of C5-C7.

Superficial back muscles (extend head and neck, elevate and retract scapula, elevate ribs)

• Trapezius: Part of origin - nuchal ligament and SP of C7.
• Levator scapulae: Origin - TVPs of C1 and C2, posterior tubercles of TVPs of C3 and C4.
• Rhomboid minor: Origin - lower end of nuchal ligament and SP of C7.
• Serratus posterior superior: Origin – lower portion of nuchal ligament and SP of C7.

Suboccipital muscles (extend and rotate head)

• Rectus capitis posterior major and minor: Origin of Major - SP of C2, Origin of Minor - posterior tubercle of TVP of C1.
• Obliquus capitis superior and inferior: Origin of Superior - TVP of C1, Origin of Inferior - SP of C2, Insertion of Inferior - TVP of C1.

Deep back muscles: spinotransversales muscles (extend neck, rotate the head)

• Splenius capitis: Part of origin - lower half dddof nuchal ligament and SP of C7.
• Splenius cervicis: Insertion - TVPs of C1-C3.

Deep back muscles: erector spinae muscles (extend the neck and head)

• Iliocostalis muscle
  • Iliocostalis cervicis: Insertion - TVPs of C4-C6.
  • Iliocostalis thoracis: Part of insertion - TVPs of C7.
• Longissimus muscle
  • Longissimus capitis: Part of Origin - TVPs of the lower three or four cervical vertebrae.
  • Longissimus cervicis: Insertion - TVPs of C2-C6.
• Spinalis cervicis: Insertion - SP of C2-C4.

Learn everything about the erector spinae muscles in our study unit:

Deep back muscles: transversospinalis muscles (extend the neck, extend and rotate the head)

• Semispinalis capitis:Origin – articular processes of C4-C7.
• Semispinalis cervicis: Insertion - SP of C2-C5.
• Semispinalis thoracis: Part of Insertion - SPs of C6 and C7.
• Multifidus: Part of Insertion - SPs of C2-C7
• Rotatores cervicis: Part of Insertion - SPs of all cervical vertebrae.