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Superficial structures of the neck: Posterior triangle

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Notes

Figure 1: Boundaries of the posterior triangle of the neck, lateral view.
Figure 2: Contents of the inferior part of the posterior triangle, lateral view.
Muscle
Origin
Insertion
Innervation
Action
Sternocleido-mastoid
Sternal head
  • Manubrium of the sternum
Clavicular head
  • Superior surface of the medial third of the clavicle
  • Mastoid process of the temporal bone
  • Superior nuchal line of the occipital bone
  • Spinal accessory nerve (CN XI)
Unilaterally:
  • Lateral flexion of the neck to the same side
  • Rotates head towards opposite side
Bilaterally:
  • Extension of the neck at the atlanto-occipital joint
  • Flexion of the neck
  • Elevation of the clavicle and manubrium (accessory respiratory muscles)
Trapezius
  • Medial third of superior nuchal line
  • External occipital protuberance
  • Nuchal ligament
  • Spinous processes of C7 - T12
  • Lateral third of the clavicle
  • Acromion & spine of the scapula
  • Elevate scapula
  • Retract scapula
  • Depress scapula
  • Upward rotation of the scapula
  • Extends neck
  • Lateral flexion to same side
Splenius capitis
  • Inferior half of the nuchal ligament and spinous processes of C7-T4
  • Mastoid process of the temporal bone
  • Lateral third of nuchal line
  • Posterior rami of middle cervical spinal nerves
  • Laterally flexes and rotates head & neck to same side
  • Extends head and neck
Levator scapulae
  • Posterior tubercles of the transverse processes of C1-4
  • Superior part of the medial border of the scapula
  • Dorsal scapular nerve
  • C3-4
  • Elevates the scapula
  • Downward rotation of scapula (Tilts glenoid cavity inferiorly by rotating scapula)
Anterior scalene
  • Anterior tubercles of the transverse processes of C3-6
  • Scalene tubercle on the first rib
  • Spinal nerves C4-6
  • Flexes neck laterally
  • Elevates 1st rib during forced inspiration
Middle scalene
  • Posterior tubercles of the transverse processes of C3-7
  • Superior surface of the first rib
  • Anterior rami of cervical spinal nerves
  • Flexes neck laterally
  • Elevates 1st rib during forced inspiration
Posterior scalene
  • Posterior tubercles of the transverse processes of c5-7
  • External border of the second rib
  • Anterior rami of C7-8
  • Flexes neck laterally
  • Elevates 2nd rib during forced inspiration
Omohyoid
  • scapula
  • Hyoid bone
  • Ansa cervicalis (C1-3)
  • Fixes or depresses hyoid bone

Transcript

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Content Reviewers

Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.),Viviana Popa, MD

The neck is the anatomical region between the base of the cranium superiorly and the clavicles inferiorly, joining the head to the trunk and limbs, and serving as a major conduit for structures passing between them.

In the neck, there are superficial structures, located in the anterior and posterior triangles, and deep structures, including the cervical viscera and prevertebral muscles.

Now, the neck is divided into the anterior and posterior triangles mainly by the borders of the sternocleidomastoid, or SCM, and trapezius muscles.

Now, the SCM is a broad, strap-like muscle which has a sternal and a clavicular head.

The sternal head is rounded and its inferior portion originates from the manubrium of the sternum, while the clavicular head is thick and its inferior portion originates from the superior surface of the medial third of the clavicle.

The two heads of the SCM are separated inferiorly, forming a superficially visible space called the lesser supraclavicular fossa, which looks like a small triangular depression.

Superiorly, the two heads of SCM join as they go toward the cranium and insert on the mastoid process of the temporal bone and the superior nuchal line of the occipital bone.

The posterior border of this muscle forms the anterior boundary of the posterior triangle.

When the SCM contracts, it produces movement at either the craniovertebral joints, or the cervical intervertebral joints, or at both.

So, unilateral contraction of SCM leads to lateral flexion of the neck to the same side, and also rotates the head so your face is turning superiorly towards the opposite side.

Bilateral contraction of SCM can lead to three different movements: extension of the neck at the atlanto-occipital joint, which makes the chin rise, flexion of the neck which makes the chin approach the manubrium, and extension of the superior cervical vertebrae combined with flexion of the inferior vertebrae which makes the chin thrust forward with head kept level.

Summary

The posterior neck triangle is an anatomical region in the posterolateral aspect of the neck. It is anteriorly bordered by the posterior border of the sternocleidomastoid, posteriorly by the anterior border of the trapezius muscle, and inferiorly by the middle third of the clavicle.

It has a roof formed by the investing layer of deep cervical fascia and a floor formed by the muscles splenius capitis, levator scapulae, middle scalene, posterior scalene, and occasionally a portion of anterior scalene, which are covered by the prevertebral layer of deep cervical fascia.

The posterior triangle is further divided by the inferior belly of the omohyoid into two other triangles: the occipital triangle located superiorly and the omoclavicular triangle located inferiorly. The posterior triangle includes arteries such as the suprascapular artery, cervicodorsal trunk, the third part of the subclavian artery and part of the occipital artery, veins such as the external jugular vein and nerves such as spinal accessory nerve, brachial plexus, and cervical plexus.