Functional Anatomy of the Cervical Spine

Original Editor - Robin Tacchetti based on the course by Daphne Xuan
Top Contributors - Robin Tacchetti, Jess Bell, Kim Jackson, Tarina van der Stockt, Ewa Jaraczewska and Vidya Acharya

Introduction

The cervical spine supports and promotes movement of the head and neck. Intervertebral discs maintain the spaces between the vertebrae. These discs act like shock absorbers throughout the spinal column to cushion the bones as the body moves. Ligaments hold the vertebrae in place, and tendons attach the muscles to the spinal column. The cervical spine is subjected to extrinsic factors such as repetitive movements, whole body vibrations and static load.

Cervical spine

Key Terms

Axes: lines around which an object rotates. The rotation axis is a line that passes through the centre of mass. There are three axes of rotation: sagittal passing from posterior to anterior, frontal passing from left to right, and vertical passing from inferior to superior. The rotation axes of the foot joints are perpendicular to the cardinal planes. Therefore, motion at these joints results in rotations within three planes. Example: supination involves inversion, internal rotation, and plantarflexion.

Bursae: reduce friction between the moving parts of the body joints. A bursa is a fluid-filled sac. There are four types of bursae: adventitious, subcutaneous, synovial, and sub-muscular.

Capsule: one of the characteristics of the synovial joints. It is a fibrous connective tissue which forms a band that seals the joint space, provides passive and active stability and may even form articular surfaces for the joint. The capsular pattern is "the proportional motion restriction in range of motion during passive exercises due to tightness of the joint capsule."

Closed pack position: the position with the most congruency of the joint surfaces. In this position, joint stability increases. For example, the closed pack position for the interphalangeal joints is full extension.

Degrees of freedom: the direction of joint movement or rotation; there is a maximum of six degrees of freedom, including three translations and three rotations.

Ligament: fibrous connective tissue that holds the bones together.

Open (loose) pack position: position with the least joint congruency where joint stability is reduced.

Planes of movement: describe how the body moves. Up and down movements (flexion/extension) occur in the sagittal plane. Sideway movements (abduction/adduction) occur in the frontal plane. The transverse plane movements are rotational (internal and external rotation).

Cervical Spine Structure

Cervical Vertebrae

There are seven cervical vertebrae, which are known as C1-C7. There role is to support the head and neck and to promote head movement. The cervical spine is only subject to relatively small weight-bearing loads. Therefore, the cervical vertebral bodies do not need to be large and "an increased range of motion takes priority over vertebral size and rigidity". However, because of this increased range of motion at the cervical spine, there is heightened injury risk for the spinal cord and the associated neurovascular structures.

Atlas - C1

The seven vertebral bodies have unique characteristics:

Atlas (C1)

• no vertebral body
• no spinous process

Axis - C2

Axis (C2)

• odontoid process (dens) extends superiorly from the anterior portion of the vertebra

C3-C6

• triangular vertebral foramen
• bifed spinous process
• transverse foramina (space for nerves and vasculature)
  

  C3-C6

C7

• singular spinous process
• larger spinous process

**In supine, it may be difficult to palpate the spinous process of C3-C6 in individuals with normal cervical lordosis.

Intervertebral Discs (IVD)

The intervertebral discs make up 25% of the height of the entire spine. However, in the cervical region, they make up 40% of the height. This increased height relative to vertebral body height provides a mobility advantage.

The nucleus pulposus of the cervical discs is gelatinous in children and young people. However, it dries out by the age of 30 years and becomes a firm, fibrocartilaginous plate.

Intervertebral disc

The following are characteristics of the cervical spine intervertebral discs:

• thicker anteriorly than posteriorly
• concave superior surface
• convex inferior surface
• movement limited by uncinate process
• anteroposterior translation does occur

** Due to location of uncinate process, posterolateral disc herniations are less frequent.

Cervical Lordosis

Typically, the cervical spine has a lordotic curvature. A lordotic posture is able to resist large compressive loads. It also helps to decrease stress on vertebral end plates. Compressive loads are distributed differently in the cervical spine compared to the thoracic and lumbar spine: the anterior column absorbs 36% of the load and the posterior facet (zygapophyseal) joints absorb 64% of the load.

Kinematics and Joints of the Cervical Spine

Kinematics

Range of Motion in Cervical Spine

The cervical spine is the most mobile part of the vertebral column.

Flexion range of motion is usually around 40 degrees and extension is around 50 degrees. The largest contributors to flexion/extension are:

• C4/C5 and C5/C6 in sitting
• C6/C7 in supine

C7/T1 contibutes the least to flexion/extension.

Lateral flexion range of motion is normally close to 30 degrees. C3/C4 and C6/C7 allow for the most movement in this plane of motion.

Cervical rotation range of motion is usually close to 70 degrees. Flexibility in this plane is mainly achieved through the C1/C2 segment.

Joints of the Cervical Spine

Joint	Location/Articulations	Function	Orientation/Composition
Intervertebral Disc Joint	Between vertebral bodies	Bear weight Facilitate motion Absorb shock
Facet (Zygapophyseal) Joints	Formed by articulations between the superior and inferior articular processes of adjacent vertebrae	Guide motion at the segmental level Determine direction of motion	Upper cervical spine = horizontal Lower cervical spine = more vertical
Uncovertebral Joint	Between the five lower cervical vertebral bodies Anteromedially to nerve root Posteromedially to vertebral artery	Control movement Limit lateral flexion
Atlanto-Axial Joint	Between atlas and axis Two lateral: interior facets of the lateral masses of C1 and superior facets of C2 One medial: between the dens of C2 and the articular facet of C1	Allow cervical rotation	Lateral: plane -type synovial joint Medial: pivot-type synovial joint
Atlanto-Occipital Joint	Between the spine and cranium Between the superior facets of the lateral masses of the atlas and the occipital condyles	Flexion and extension of the head on the neck Lateral flexion	Condyloid-type synovial joint

Spinal Ligaments

Ligaments Unique to the Cervical Spine

Ligament	Origin	Insertion	Role/Function
Nuchal ligament	Occiput	Tips of the spinous process from C1-C7	Limits hyperflexion
Transverse ligament		Attaches to lateral masses of atlas	Anchors dens in place
Apical ligament	Dens of the axis	Foramen magnum	Stabilises skull on spine
Alar Ligament	Dens of the axis	Occiput	Limits atlanto-axial rotation
Cruciform or Cruciate Ligament 1. Superior longitudinal band 2. Inferior longitudinal band 3. Transverse band	Superior: transverse band Inferior: transverse band Transverse: dens of axis	Superior: foramen magnum Inferior: second vertebral body Transverse: between the lateral masses of the atlas	Holds dens in place

Muscles of the Cervical Spine

The muscles of the cervical spine can be divided by location or by the movement they create.

Anterior vertebral muscles

Anterior (Prevertebral) Vertebral Muscles

• Rectus capitis anterior
• Rectus capitis lateralis
• Longus capitis
• Longus colli/ Longus cervicis (3 portions: superior oblique, inferior oblique, vertical)

Also known as the deep cervical (neck) flexors.

Lateral Vertebral Muscles

Scalenes

• anterior
• middle
• posterior
• minimus (not always present)

Lateral view of cervical muscles

Posterior Vertebral Muscles

These can be further divided into intrinsic and extrinsic muscles.

Extrinsic muscles

• Trapezius
• Levator scapulae

Intrinsic muscles

Posterior muscles of the cervical spine

• Superficial muscles :
  • splenius capitis
  • splenius cervicis
• Deep muscles:
  • suboccipital group
    • rectus capitis posterior major
    • rectus capitis posterior minor
    • obliquus capitis inferior
    • obliquus capitis superior
  • transversospinalis muscles
    • semispinalis capitis
    • semispinalis cervicis
    • rotatores cervicis
    • multifidus (these are also known as deep neck extensors)
  • interspinales and intertransversarii

Movement

Motion	Flexion	Extension	Lateral Flexion	Rotation
Muscles	Longus colli Sternocleidomastoid Scalene anterior Longus capitis Rectus capitis anterior (head only)	Iliocostal cervicis Splenius cervicis Splenius capitis Trapezius Erector spinae Rectus capitis posterior, major and minor (head only)	Scalene anterior, medius and posterior Sternocleidomastoid Splenius capitis Trapezius Erector spinae Rectus capitis lateralis (head only)	Semispinalis cervicis Multifidus Scalene anterior Splenius cervicis and capitis Sternocleidomastoid Inferior oblique (head only) Rectus captitis posterior major (head only)

The following tables identify the origin, insertion, innervation and action of key cervical muscles. Muscles with multiple functions are repeated in the relevant tables.

Cervical Spine Flexors

Muscle	Origin	Insertion	Innervation	Action
Rectus capitis anterior	Lateral mass and transverse process of atlas (C1)	Basilar part of occipital bone	Anterior rami of 1st and 2nd cervical spinal nerves (C1, C2)	Flexion of head at atlanto-occipital joint
Longus colli	Transverse processes of C3-C5 and the vertebral bodies of C5-T3	Anterior tubercle of C1, the vertebral bodies of C2-C4, and the transverse processes of C5 and C6.	Anterior rami of the 2nd to 6th cervical spinal nerves (C2-C6)	Unilateral contraction: neck lateral flexion (ipsilateral), neck rotation (contralateral) Bilateral contraction: neck flexion
Longus capitis	Transverse processes of C3-C6	Occipital bone	Anterior rami of 1st to 3rd cervical spinal nerves (C1-C3)	Unilateral contraction: rotation of the head (ipsilateral) Bilateral contraction: flexion of the head and neck
Anterior scalene	Transverse processes of C3-C6	First rib	Anterior rami of 4th to 6th cervical spinal nerves (C4-C6)	Unilateral contraction: neck lateral flexion (ipsilateral), neck rotation (contralateral), elevation of the first rib Bilateral contractions: neck flexion
Sternocleidomastoid	Manubrium and the medial portion of the clavicle	Mastoid process of the temporal bone	Accessory nerve (CN XI), branches of cervical plexus (C2-C3)	Unilateral contraction: ipsilateral neck flexion, elevation of the chin, contralateral rotation of head Bilateral contraction: extension of the upper vertebral joints, extension of the neck and head, elevation of the head, elevation of the sternum and clavicle, expansion of the thoracic cavity
Rectus capitis lateralis	Transverse process of atlas (C1)	Jugular process of occipital bone	Anterior rami of 1st and 2nd cervical spinal nerves (C1-C2)	Lateral flexion of the head (ipsilateral), stabilisation of the atlanto-occipital joint

Cervical Spine Extensors

Muscle	Origin	Insertion	Innervation	Action
Obliques capitis superior	Transverse process of the atlas	Occipital bone	Suboccipital nerve (posterior ramus of 1st cervical spinal nerve (C1))	Stabilises the atlanto-occipital joint
Oblique capitis inferior	Spinous process of the axis	Tansverse process of atlas	Suboccipital nerve (posterior ramus of 1st cervical spinal nerve (C1))	Stabilises the atlanto-occipital joint
Rectus capitis posterior major	Spinous process of C2	Occipital bone	Suboccipital nerve (posterior ramus of 1st cervical spinal nerve (C1))	Unilateral contraction: head rotation (ipsilateral) Bilateral contraction: head extension
Rectus capitis posterior minor	Posterior tubercle of the atlas	Occipital bone	Suboccipital nerve (posterior ramus of 1st cervical spinal nerve (C1))	Head extension
Iliocostal cervicis	Ribs 3-6	Transverse process of C4-C6	Dorsal rami of the upper thoracic and lower cervical spinal nerves	Laterally flexes and extends the lower cervical region
Trapezius	Occipital bone, nuchal ligament and spinous process C7-T12	Lateral third of the clavicle, acromian and spine of the scapula	Spinal root of accessory nerve (CN XI) (motor) Cervical nerves (C3 and C4) (pain and proprioception)	Supports the spinal column to remain erect
Spelnius cervicis	Spinous process of T3-T6	Transverse process of C1-C3	Dorsal rami of cervical spinal nerves (C5-C8)	Acting bilaterally: extend the neck
Splenius capitus	Spinous process of C7-T3 and nuchal ligament	Occipital bone	Posterior rami of the 2nd and 3rd cervical spinal nerves	Acting bilaterally: extension of the head and cervical spine

** The transversospinal muscles (rotatores, multifidus, semispinalis) are the deep muscle of the spine. They attach between the transverse and spinous process of the vertebrae. They stabilise and extend the spine. The rotatores also provide rotation.

Cervical Spine Lateral Flexors

Muscle	Origin	Insertion	Innervation	Action
Splenius cervicis	Spinous process of T3-T6	Transverse process C1-C3	Dorsal rami of cervical spinal nerves (C5-C8)	Acting unilaterally: lateral flexion and rotation of the head and neck to the ipsilateral side
Splenius capitis	Spinous process of C7-T3 and nuchal ligament	Occipital bone	Posterior rami of the 2nd and 3rd cervical spinal nerves	Acting unilaterally: lateral flexion of the head and neck and rotation the head to the ipsilateral side
Sternocleidomastoid	Manubrium and the medial portion of the clavicle	Mastoid process of the temporal bone	Accessory nerve (CN XI), branches of cervical plexus (C2-C3)	Unilateral contraction: ipsilateral neck flexion, elevation of the chin, contralateral rotation of headBilateral contraction: extension of the upper vertebral joints, extension of the neck and head, elevation of the head, elevation of the sternum and clavicle, expansion of the thoracic cavity
Middle scalene	Posterior tubercles of the transverse processes of C2-C7	Scalene tubercle of the first rib	Anterior rami of C3-C8	Elevation of the first rib. Ipsilateral contraction causes ipsilateral lateral flexion of the neck
Posterior scalene	Posterior tubercles of the transverse processes of C5-C7	2nd rib	Anterior rami of C6-C8	Elevation of the second rib, and ipsilateral lateral flexion of the neck
Trapezius	Occipital bone, nuchal ligament and spinous process C7-T12	Lateral third of the clavicle, the acromian and the spine of s scapula	Spinal root of accessory nerve (CN XI) (motor) Cervical nerves (C3 and C4) (pain and proprioception)	Side bending
Rectus capitis lateralis	Superior surface of the transverse process of atlas	Inferior surface of the jugular process of the occipital bone	Anterior rami of C1-C2 spinal nerves	Stabilizes the atlanto-occipital joint; head lateral flexion (ipsilateral)

Cervical Spine Rotators

Muscle	Origin	Insertion	Innervation	Action
Rectus capitis posterior major	Spinous process of C2	Occipital bone	Suboccipital nerve (posterior ramus of 1st cervical spinal nerve (C1))	Unilateral contraction: head rotation (ipsilateral) Bilateral contraction: head extension
Rectus capitis posterior major	Spinous process of C2	Occipital bone	Suboccipital nerve (posterior ramus of 1st cervical spinal nerve (C1))	Unilateral contraction: head rotation (ipsilateral) Bilateral contraction: head extension
Sternocleidomastoid	Manubrium and the medial portion of the clavicle	Mastoid process of the temporal bone	Accessory nerve (CN XI), branches of cervical plexus (C2-C3)	Unilateral contraction: ipsilateral neck flexion, elevation of the chin, contralateral rotation of head Bilateral contraction: extension of the upper vertebral joints, extension of the neck and head, elevation of the head, elevation of the sternum and clavicle, expansion of thoracic cavity
Splenius capitis	Spinous process ofC7-T3 and nuchal ligament	Occipital bone	Posterior rami of the 2nd and 3rd cervical spinal nerves	Acting unilaterally: lateral flexion of the head and neck and rotation of the head to the ipsilateral side
Splenius cervicis	Spinous process T3-T6	Transverse process C1-C3	Dorsal rami of cervical spinal nerves (C5-C8)	Acting unilaterally: lateral flexion and rotation of the head and neck to the ipsilateral side

Innervation of the Cervical Spine

Nerves originating from the cervical plexus innervate the muscles of the neck. Each nerve root in the cervical spine exits above its corresponding nerve root. There are eight pairs of cervical nerves despite the presence of seven cervical vertebrae. The C8 nerve root exits below the seventh cervical vertebra. The accessory nerve which is cranial nerve XI innervates sternocleidomastoid and trapezius.

Nerve	Motor	Sensory
C1	Head and neck extensors Rectus capitus anterior and lateral, longus capitus
C2	Head and neck extensors Rectus capitus anterior and lateral, longus capitus, longus colli	Lateral occiput and submandibular area
C3	Head and neck extensors Longus capitus, longus colli, levator scapulae, scaleni, trapezius, diaphragm	Lateral occiput and lateral neck, overlapping C2
C4	Head and neck extensors Longus capitus, longus colli, levator scapulae, scaleni, trapezius, diaphragm	Lower lateral neck and medial shoulder area
C5	Deltoid, biceps, bicep tendon reflex	Clavicle level and lateral arm
C6	Biceps, wrist extensors (brachioradialis tendon reflex)	Lateral forearm, thumb, index and half of 2nd finger
C7	Wrist flexors, triceps (triceps tendon reflex)	Second finger
C8	Finger flexors, interossei	Medial forearm, ring and little finger
T1	Interossei	Medial arm

Vascular Supply of the Cervical Spine

Vertebral arteries, veins and nerves pass through the transverse foramina of the cervical vertebrae. C7 is the only exception in that the vertebral artery passes around the vertebra instead of through the transverse foramen. The neural components sit posterior to the vertebral artery.

The cervical spine vascular supply is primarily provided by the vertebral arteries on each side of the spine. These arteries arise from the subclavian arteries, which originate directly from the arch of the aorta on the right, and the brachiocephalic trunk on the left.

** The common carotid artery bifurcates into the internal and external carotid arteries at the C3 segmental level. Only the external carotid artery provides any blood supply to the neck.

Clinical Relevance

• Atlanto-axial instability (AAI) can have serious neurological consequences:
  • conditions with the potential for AAI include:
    • rheumatoid arthritis
    • Down syndrome:
      • laxity in the transverse ligament is present in 14-22% of individuals with Down syndrome.

• A tight sternocleidomastoid muscle can cause torticollis.
• Disc herniation:
  • disc herniations in the cervical spine are a lot less common than in the lumbar spine
  • typical locations:
    • C5-C6
    • C6-C7
• Because the prevertebral cervical muscles stabilise the neck, dysfunction in these muscles can cause cervicogenic pain
• Trigger points that develop in the suboccipital muscles can refer pain to the head causing cervicogenic headaches

Resources

• Functional Anatomy of the Thoracic Spine and Rib Cage
• Functional Anatomy of the Lumbar Spine and Abdominal Wall
• Cervical Deep Neck Extensors
• Cervical Deep Neck Flexors