The cervical spine is formed by the first seven vertebrae which are named as C1 to C7 and make the neck region of the spine.
Anatomically, the cervical spine starts where the top vertebra (C1) connects to the bottom of the skull.
The normal cervical spine has a lordosis. That means it is curved with convexity on the anterior aspect. It ends when C7 joins with the first thoracic vertebra.
Understanding the cervical spine anatomy is vital to understand the various problems and abnormalities of the neck. Cervical spine anatomy is better understood by dividing it into upper and lower cervical regions.
The cervical spine connects the skull to the thoracic spine. It also functions to provide mobility and stability to the head.
Upper Cervical Spine
The cervical spine begins with C1 vertebrae but because the lower part of the skull articulates with cervical spine, therefore, the important structures are considered along with.
The bones of the upper cervical spine include
- The base of the skull surrounding the foramen magnum
- Pair of occipital condyles
- Atlas vertebra (C1)
- Axis vertebra (C2)
The occipital condyles are under-surface facets of the occipital bone which articulates with the superior facets of the atlas vertebra.
The condyles are oval in shape, and their anterior extremities, and they are directed forward and medialward.
The articular surfaces of the condyles are convex from before backward and from side to side and look downward and lateralward.
Occipital condyles are covered by hyaline cartilage.
Atlas or C1 vertebra is the first cervical vertebra of the spine.
It is named for the Atlas of mythology because it supports the globe of the head.
The atlas along with the Axis (C2)– forms the joint connecting the skull and spine and are specialized to allow a greater range of motion.
Together they are responsible for the nodding and rotation movements of the head.
50% of the rotation occurs at the atlantoaxial joint whereas atlanto-occipital joint is responsible for 50% of flexion and extension.
Odontoid process or dens that is part of the C2 vertebra actually is part of C1 developmentally.
The odontoid process is kept close to the posterior aspect of the anterior arch of the atlas by the transverse ligament mainly and aided by the apical and alar ligaments.
Atlas has no body and consists of
- A thick anterior arch
- A thin posterior arch
- Two lateral masses
- Two transverse processes
The transverse foramen is present in the transverse processes. The vertebral artery passes through it.
It appears like a ring.
Two lateral masses on either lateral side provide the bulk of the atlas bone mass. The transverse foramina are located to the lateral aspect of the lateral masses.
There are two kidney-shaped superior articular facets. They are directed upward and inward to articulate with the occipital condyles, which face downward and outward.
The inferior articular facets are relatively flat and face downward and inward to articulate with the superior facets of the axis.
Read More| Anatomy of Atlas Vertebra
The axis is the second vertebra and has a unique shape. It consists of a large vertebral body and a pars articularis separating the superior from inferior articular processes.
The odontoid process articulates with the anterior arch of the atlas via its anterior articular facet and is held in place by the transverse ligament.
The parts of the rest of the axis vertebra are
- Vertebral body
- Transverse processes
- Superior and inferior articular processes
The odontoid process or dens is a 2 to 3 cm long corticocancellous structure with a narrowed waist and thickened cortical tip emanating in a rostral (towards the head) direction from the vertebral body.
The odontoid rests in a recess behind the anterior arch of the atlas and the medial walls of the two lateral masses.
The superior articular surface of the axis is the cranial (towards the head) surface of the vertebral body of the axis and lies separated by a narrow osseous recess lateral to the odontoid.
The two inferior articular processes of the axis are located on the inferolateral corner of the neural arch. The transverse foramen of the axis is located in the lateral aspect of the vertebral bodies on either side.
Read More| Anatomy of Axis Vertebra
Lower Cervical Spine or Subaxial Spine
The lower cervical spine or subaxial [below axis vertebra] cervical spine, includes the C3 to C7 vertebrae. These lower cervical vertebrae have a relatively uniform anatomic configuration but are quite dissimilar to C1 and C2 vertebrae.
Each of these vertebrae has a vertebral body that is concave on its superior surface and convex on its inferior surface.
The vertebral body is larger in coronal (left to right) than its sagittal diameter (anterior to posterior).
On their superior surfaces, these vertebrae have raised processes or hooks called uncinate processes. Each uncinate process articulates with a depressed area [anvil or enchancrure] on the inferior lateral aspect of the superior vertebral body.
This joint marks the lateral extent of the vertebral body.
Intervertebral discs are present between the vertebral bodies of C2-C7.
Disc has four parts
- Nucleus pulposus in the center
- Annulus fibrosis surrounds the nucleus
- Two end plates attached to the adjacent vertebral bodies.
Discs serve as shock absorbers and help in load transmission. Cervical discs are thicker anteriorly and thus contribute to normal cervical lordosis.
C3-C6 vertebrae have a typical anatomical structure –
- Small body, and broader from side to side than from front to back.
- Flattened anterior and posterior surfaces
- The upper surface
- Concave transversely
- Presents a projecting lip on either side.
- The lower surface
- Concave from front to back
- Convex from side to side
- On either side laterally they have shallow concavities
- Concavities receive uncinate processes to form uncovertebral joints
- The vertebral foramen is large and of a triangular form.
- The transverse processes are each pierced by the foramen transversarium
Transverse foramina are present consistently in the upper six vertebrae but variable in C7. Even when it is present, it is small.
The transverse foramen is formed by the fusion of the anterior and posterior parts of the transverse process and part of the pedicle.
Transverse foramina give passage to the vertebral artery and vein in the upper six cervical vertebrae. In C7 it contains only vein as well as a plexus of sympathetic nerves.
C7 has an enlarged spinous process called vertebra prominens. It is the most prominent structure that can be palpated when we pass our finger downwards from the skull.
Neural foramina of cervical spine allow exit of cervical spinal nerves which are eight in number and are named as C1 to C8.
Between two adjacent vertebrae is interposed intervertebral disc.
From vertebral bodies, pedicles project from anteromedial to posterolateral direction.
Articular facets are flat
- Superior articular facets face backward, upward, and slightly medially
- The Inferior facets are forward, downward, and slightly laterally.
The facet joints are diarthrodial joints formed by superior and inferior articular processes. They are also known as the zygapophyseal articulations. The articular surfaces are angled approximately 45 degrees in relation to the transverse axis and about 85 degrees in the sagittal plane. This orientation is important for weight transmission and prevention of anterior translation.
The fibrous capsules are well innervated and the nerve endings [mechanoreceptors] are found more in cervical spine than rest of the spine. These carry proprioception and pain sensation and may be involved in modulation of muscle reflexes for preventing joint instability and degeneration.
The facet joints in the cervical spine are innervated by both the anterior and posterior rami.
The pillar of bone between the superior and inferior articular processes is commonly referred to as the lateral mass and is It is a useful site for posterior screw or wire stabilization.
The laminae are narrow, and thinner above than below.
The laminae arise from the posteromedial border of the lateral masses project posterior and toward the midline to form bifid spinous processes.
The spinous process is short and bifid.
Ligamentum flavum or yellow ligament is present between space between two laminae.
Ligaments like interspinous and supraspinous ligaments or ligamentum nuchae form a posterior ligamentous complex and its disruption may lead to mechanical instability.
The longus colli muscles lie directly over and insert onto the anterolateral aspects of each cervical vertebra.
The sympathetic plexus lies on top of the lateral muscle belly and maybe injured aggressive dissection or retraction which can lead to Horner’s syndrome.
The prevertebral (deep) and alar (superficial) fascial layers separate the spine from the overlying esophagus.
Columns of Cervical Spine
The cervical spine can be said to be made up of anterior and posterior columns.
The anterior column consists
- Anterior longitudinal ligament
- Anterior two-thirds of
- the vertebral bodies
- Annulus fibrosus
- Intervertebral discs
The middle column is formed by
- Posterior longitudinal ligament
- Posterior one-third of
- Vertebral bodies
- Annulus fibrosus
- Intervertebral discs
The posterior column is posterior arches that include
- Transverse processes
- Articular facets
- Spinous processes
Three columns have their significance in case of injury. If there is an injury to one column, the other two provide stability. But if two are disrupted, injury to the cord is more likely because the spine may then move as w separate units.
Ligaments provide stability to the cervical spine. The upper cervical spine is inherently unstable and therefore ligament integrity is very important in this region.
Anterior and posterior longitudinal ligaments maintain help stabilizing the anterior and middle columns and are the major stabilizers of the intervertebral joints.
Both of these run almost the entire length of the spine. ALL have more closely adhered to the discs than PLL.
Anterior longitudinal ligament is not that well developed in the cervical spine though. It becomes the anterior atlanto-occipital membrane at the level of the atlas, whereas the PLL merges with the tectorial membrane.
The PLL prevents excessive flexion and distraction.
Posterior column is supported by following ligaments that maintain stability between the vertebral arches.
- Nuchal ligament – Continuation of the supraspinous ligament in the cervical spine.
- Capsular ligaments
- Ligamentum flavum – connects adjacent laminae of two vertebrae, also connects to and reinforces the facet joint capsules ventrally.
- Interspinous ligament – Between adjacent spinous process
- Supraspinous ligament- Runs along the tips of the spinous processes
The interspinous ligament and the ligamentum flavum control for excessive flexion and anterior translation.
Nuchal ligament is a stabilizer of the cervical spine.
The upper cervical spine has specialized external and internal ligaments secure the craniocervical junction and the atlantoaxial joints are secured by the external and internal ligaments.
The external ligaments are consist of the atlanto-occipital and anterior longitudinal ligaments.
The internal ligaments are
- The transverse ligament connects the medial wall of the anterior third of either lateral mass of the atlas with one another. It holds the odontoid process in place against the posterior atlas and prevents anterior subluxation of C1 on C2.
This ligament allows rotation of the atlas on the dens and stabilizes the cervical spine during flexion, extension, and lateral bending.
The transverse ligament is considered as the most important ligament for preventing abnormal anterior translation.
- The accessory ligaments arise posterior to the transverse ligament and insert into the lateral aspect of the atlantoaxial joint. These become maximally taut with 5-8° of head rotation, lax with cervical extension, and maximally taut with 5-10° of cervical flexion.
- The apical ligament connects between a bony protuberance of the basion (The mid-point on the anterior margin of the foramen magnum on the occipital bone) to the superior tip of the odontoid.
- The alar ligaments connect the medial surface of the occipital condyles to the lateral tip of the odontoid. The paired alar ligaments secure the apex of the odontoid to the anterior foramen magnum.
These prevent excessive lateral and rotational motion while allowing flexion and extension.
- Tectorial membrane is the continuation of the posterior longitudinal ligament to the anterior margin of the foramen magnum and is composed of a deep and superficial layer.
Between the apical ligament and the deep layer of the tectorial membrane is the cruciate ligament bridging the basion and the axis body and a narrow transverse ligament, which extends between the upper ends of the lateral masses of the atlas.
Posteriorly, the upper cervical spine does not have well-developed ligamentous support structures.
The atlanto-occipital and atlantoaxial joint capsules are additional well-defined ligamentous support structures.
Muscles of Cervical Spine
Broadly speaking, spinal muscles are of the following types. The location of muscle is also given
- Forward flexors are anterior
- Lateral flexors are lateral
- Rotators are lateral
- Extensors are posterior
The cervical spine has many specialized muscles for the complex movements it achieves. They are listed below
It originates by two heads –
- Sternal head- Superoanterior surface of the manubrium of the sternum
- Clavicular head- Superior surface of the medial third of the clavicle
It inserts into the lateral surface of mastoid process and lateral half of the superior nuchal line [a curved line on the occipital bone].
The sternocleidomastoid muscle is supplied by the accessory nerve (it is also called eleventh cranial nerve), and anterior rami of spinal nerves C2-C3
Sternocleidomastoid is an external rotator and extensor of the head. It also flexes the neck.
These are a group of three pairs of muscles in the lateral neck.
- Anterior scalene or scalenus anterior
- Lies behind the sternocleidomastoid muscle
- Anterior tubercles of the transverse processes of the C3-C6
- Inserts on scalene tubercle on the inner border of the first rib and ridges of the second rib
- Supplied by the anterior ramus C5 and 6.
- Middle scalene or scalenus medius
- Largest and longest of the three
- It originates from the posterior tubercles of the transverse processes of the lower six cervical vertebrae.
- Inserts into the upper surface of the first rib
- The brachial plexus and the subclavian artery pass anterior to it.
- Posterior scalene or scalenus posterior
- Smallest and deepest
- Arises from the posterior tubercles of the transverse processes of the lower two or three cervical vertebrae
- Inserts into the outer surface of the second rib
- Supplied by cervical nerves C6, C7, and C8.
Scalenus muscles are flexors and rotators of the neck.
The spinalis is a part of the erector spinae muscle located nearest to the spine. It has three regional parts spinalis cervicis and spinalis capitis are in the neck region whereas spinalis dorsalis is in the thoracic region.
Spinalis cervicis or spinalis Colli originates from the lower part of the nuchal ligament [a ligament at the back of the neck], the spinous process of the C7 and , and sometimes T1 and 2. It is inserted into the spinous process of the axis and sometimes C3 and C4 as well.
Spinalis capitis extends from C7 and T1 and blends with semispinalis capitis.
These are supplied by nerves from middle or lower cervical rami.
These are three muscles just like spinalis thoracis, cervicis, and capitis.
Semispinalis Capitis arise from the tips of the transverse processes upper 6-7 thoracic and C7 vertebrae, from the articular processes of C4-C6 vertebrae. These unite to form tendon and inserted between the superior and inferior nuchal lines of the occipital bone.
It rotates & pulls head backward. It is supplied by anterior rami of C1 – C5.
Semispinalis cervicis or semispinalis colli arises from the transverse processes T1-T6 vertebrae and is inserted into the spinous processes from C2 -C5. It extends & rotates vertebral column. This muscle is supplied by rami middle/lower cervical nerves.
This muscle originates T3-T6 spinous processes and inserts into the posterior tubercles of the transverse processes of the C1-3 cervical vertebrae.
It extends vertebral column.
The muscle is innervated by middle or lower cervical nerves.
Longus Colli Cervicis
It is a paired muscle on the anterior aspect of the cervical spine.
It originates from
- Anterior tubercles of transverse processes of vertebrae C3-C5 [superior part]
- Anterior surface of bodies of vertebrae C5-T3 [Intermediate part]
- Anterior surface of bodies of vertebrae T1-T3 [inferior part]
- Superior part- anterior tubercle of vertebra C1
- Intermediate part- anterior surface of bodies of vertebrae C2-C4
- Inferior part: Anterior tubercles of transverse processes of vertebrae C5-C6
Longus colli cervicis is a flexor of cervical spine. It is supplied by anterior rami of spinal nerves C2-C6
This muscle is also situated anterior to the cervical vertebrae. It arises from the anterior tubercles of the transverse processes of C3-C6 vertebrae. It converges towards its opposite counterpart and inserts on the inferior surface of the basilar part of the occipital bone.
Longus capitus is innervated by a branch of cervical plexus [C1-C3]. Longus capitis flexes the head and neck laterally rotates it.
Rectus Capitus Anterior
The rectus capitis anterior or rectus capitis anticus minor is situated immediately behind the upper part of the longus capitis.
Its origin is from the anterior surface of the lateral mass of the atlas and from the root of its transverse process.
It is inserted into the inferior surface of the basilar part of the occipital bone immediately in front of the foramen magnum.
It aids in the flexion of the head and the neck.
It is supplied by C1, C2 nerve rami.
Rectus Capitus Lateralis
The rectus capitis lateralis originates from the upper surface of the transverse process of the atlas. The muscle is inserted into the undersurface of the jugular process of the occipital bone.
This muscle bends the head laterally and is supplied by C2, C3 rami.
This muscle extends the cervical vertebrae. It is supplied by middle or lower cervical nerves
The muscle originates from angles of ribs 3-6 and inserts into transverse processes of C4-C6
Longissimus cervicis is an extensor of cervical vertebrae and is supplied by middle or lower cervical rami.
The longissimus is the longest subdivision of the erector spinae muscle and is lateral to semispinalis muscle.
The longissimus cervicis arises from the transverse processes of T1-5. It inserts into the posterior tubercles of the C 2–6.
It rotates pulls the head backward. It is supplied by middle or lower cervical rami.
Rectus Capitus Anterior
The rectus capitis anterior muscle is behind longus capitis. It originates from the lateral mass of the atlas, and the root of its transverse process. It inserts into basilar part of the occipital bone immediately in front of the foramen magnum.
It helps in flexion of the head. It is supplied by C1, C2 nerves.
Rectus Capitus Posterior
The rectus capitis posterior major takes origin from the spinous process of the axis, and inserts into the lateral part of the inferior nuchal line of the occipital bone and the surface below the line.
It is a minor extensor of the head and is supplied by suboccipital
Obliquus Capitus Inferior
The obliquus capitis inferior originates from the spinous process of the C2 or the axis vertebra. It is directed laterally and slightly upward and inserts into the transverse process of the atlas.
It rotates atlas and is supplied by suboccipital nerve.
Obliquus Capitus Superior
The obliquus capitis superior muscle takes origin from the lateral mass of the atlas bone and inserts into the inferior nuchal line of the occipital bone.
It extends the head and also aids in its lateral flexion. It is supplied by suboccipital nerve.
Cervical Spinal Cord and Nerves
The spinal cord at the craniocervical junction is located between the posterior halves of the lateral masses of the atlas and the pars interarticularis of the axis. It fills about 50% of the neural canal in the upper cervical spine.
The cervical cord is enlarged in the lateral dimension and spans 13-14 mm in this plane whereas the anteroposterior extent is 7 mm.
Cerebrospinal fluid occupies an additional 1 mm and another millimeter for dura.
From the spinal cord, at each vertebral level spinal nerves exit through neural foramina to supply their respective regions.
Boundaries of neural foramen are
- Anteromedially – uncovertebral joints
- Posterolaterally – facet joints
- Superiorly – pedicle of the superior vertebra
- Inferiorly- pedicle of the lower vertebra
- Medially- Edge of the endplates and the intervertebral discs.
The foramina are largest at C2-C3. they progressively decrease in size down to C6-C7. Spinal nerve occupies 25-33% of the foraminal space.
The spinal nerves exit above their correspondingly numbered vertebral body from C2-C7.
The first nerve C1 is between the occiput and the atlas (C1) and the eighth nerve exists between C7 and T1.
There are many interconnections present between the sympathetic nervous system and the spinal nerve proper.
The cervical nerves control many bodily functions and sensory activities. A rough estimation is as follows
C1: Head and neck
C2: Head and neck
C4: Upper body (e.g. Deltoids, Biceps)
C5: Wrist extensors
C6: Wrist extensors
Injury to cervical spine or involvement of spinal nerves affects the area they supply.
Blood supply of Cervical Spine
The vertebral arteries emerge from the transverse foramina of the vertebral body of the axis in a cranial direction lateral to the pars interarticularis and atlantoaxial joints.
The vertebral arteries pass through the foramen magnum to become the basilar artery.
Before they unite to form, basilar artery, each vertebral arteries give off a branch that unite to form the anterior spinal artery which travels down the spinal cord through the anterior sulcus.
The posterior spinal arteries either can originate from the posterior inferior cerebellar artery or branches from the pre-atlantal vertebral arteries. There are two posterior spinal arteries, one on each side.
These also travel caudally down the spinal cord but through the two posterior sulci.
The anterior spinal artery provides blood to the anterior two-thirds of the spinal cord and rest is by posterior
The mid-cervical spinal cord receives vascular supply by segmental medullary arteries coming from directly off the vertebral artery.
Nerve Supply of Cervical Spine
The atlanto-occipital and atlantoaxial joints are supplied by the anterior rami of the first and second cervical spinal nerves. [Read more on spinal nerves]
Facet joints are supplied both by anterior and posterior rami.
- The C2-C3 facet joint is innervated
- Two branches of the posterior ramus of the third cervical spinal nerve
- A communicating branch
- A medial branch [also known as the third occipital nerve.]
- C3-C4 to C7-T1 facet joint, are supplied by
- Posterior rami medial branches that arise 1 level cephalad and caudad to the joint
- Therefore, each facet joint is innervated by the medial branches above and below.