Trapezius Anatomy

Upper Trapezius

Origin: External occipital protuberance,Medial third of the superior nuchal line, Nuchal ligament, Spinous process of C7
Insertion: Lateral third of the clavicle, Medial aspect of the acromion process of the scapula
Action: Upward rotation of the scapula, Elevation of the scapula
Innervation: Spinal accessory nerve (cranial nerve XI) and the ventral rami of spinal nerves C2, 3, 4 (for sensory function)
Blood Supply: Branches from the thyrocervical trunk

Primary Actions of the Upper Trapezius

1. Upward rotation of the scapula

Agonists:

  • Serratus anterior (lower part)
  • Trapezius (lower part)

 Antagonists:

  • Levator scapulae
  • Serratus anterior (upper part)
  • Rhomboid major
  • Rhomboid minor
  • Pectoralis minor

2. Elevation of the scapula

  Agonists:

  • Levator Scapulae

  Antagonists:

  • Serratus anterior (lower part)
  • Trapezius (lower part)
  • Pectoralis minor

Secondary Actions of the Upper Trapezius

1. Assists with extension of the cervical spine

Agonists:

  • Sternocleidomastoid
  • Rectus Capitis Posterior Major
  • Rectus Capitis Posterior Minor
  • Obliquus Capitis Superior
  • Splenius Cervicis
  • Splenius Capitis
  • Ilocostalis Cervicis
  • Longissimus Cervicis
  • Longissimus Capitis
  • Spinalis Cervicis
  • Spinalis Capitis
  • Semispinalis Cervicis
  • Semispinalis Capitis

Antagonists: 

  • Longus Colli
  • Longus Capitis
  • Anterior Scalene
  • Sternocleidomastoid

2. Assists with lateral flexion of the cervical spine

  Agonists:

  • Longus colli
  • Rectus capitis lateralis
  • Scalenes
  • Sternocleidomastoid
  • Obliquus capitis superior
  • Splenius cervicis
  • Splenius capitis
  • Iliocostalis cervicis
  • Longissimus capitis

Antagonists: Same muscles on the contralateral side

  • Longus colli
  • Rectus capitis lateralis
  • Scalenes
  • Sternocleidomastoid
  • Obliquus capitis superior
  • Splenius cervicis
  • Splenius capitis
  • Iliocostalis cervicis
  • Longissimus capitis

3. Assists with contralateral rotation of the head and cervical spine when acting unilaterally

Agonists:

  • Semispinalis capitis
  • Semispinalis cervicis
  • Multifidus
  • Sternocleidomastoid

Antagonists: Same muscles on the contralateral side

  • Semispinalis capitis
  • Semispinalis cervicis
  • Multifidus
  • Sternocleidomastoid

Anterior scalene, middle scalene, the rotatores, and longus colli (inferior oblique) assist with contralateral rotation of the head and cervical spine.

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Middle Trapezius

Origin: Spinous processes of T1 to T5
Insertion: Medial edge of the superior surface of the acromion process of the scapula, The superior edge of the scapular spine
Action: Retraction of the scapula
Innervation: Spinal accessory nerve (cranial nerve XI), The ventral rami of spinal nerves C2, C3, C4
Blood Supply: Branches from the thyrocervical trunk

Primary Actions of the Middle Trapezius

1.  Retraction of the scapula

 Agonists:

  • Rhomboid major
  • Rhomboid minor

  Antagonists: 

  • Serratus anterior
  • Pectoralis minor

Lower Trapezius

Origin: Spinous processes of T6 to T12
Insertion: Tubercles at the apex of the scapular spine
Action: Upward rotation of the scapula
Innervation: Spinal accessory nerve (cranial nerve XI), The ventral rami of spinal nerves C2, C3, C4
Blood Supply: Branches from the thyrocervical trunk

Primary Actions of the Lower Trapezius

1. Upward rotation of the scapula

Agonists:

  • Trapezius (upper part)
  • Serratus anterior (lower part)

Antagonists: 

  • Levator scapulae
  • Serratus anterior (upper part)
  • Rhomboid major
  • Rhomboid minor
  • Pectoralis minor

2. Depression of the scapula

  Agonists:

  • Serratus anterior (lower part)
  • Pectoralis minor

  Antagonists:

  • Trapezius (upper part)
  • Levator scapulae