VH Dissector: Head & Neck: Posterior Triangle

Begin with the Trapezius added to the shoulder

The Sternocleidomastoid divides the neck into the anterior and posterior triangles. The posterior triangle is bounded by the posterior border of the sternocleidomastoid muscle (anteriorly) and the anterior border of the trapezius muscle (posteriorly) and by the middle 1/3 of the clavicle inferiorly.

Origin - manubrium of the sternum and medial 1/3 of the clavicle.

Insertion - mastoid process of the temporal bone (and a small part of the occipital bone).

Innervation - Spinal Accessory Nerve (Cranial Nerve XI).

Action - Unilaterally causes the contralateral rotation of the face and ipsilateral neck side bending. When acting bilaterally they help flex the neck.

Remove the Sternocleidomastoid and add the Splenius Capitus – runs from the ligamentum nuchae and spinous processes of the superior thoracic vertebrae to the mastoid process and superior nuchal line.  *DO NOT WORRY ABOUT THIS MUSCLE NOW. IT WILL BE COVERED IN NEURO I THEME. YOU SHOULD BE ABLE TO IDENTIFY IT AT THIS POINT BUT THAT IS ALL. *

Add the Posterior Scalene.

Origin - Posterior tubercles of transverse processes of C5-C7 vertebrae.

Insertion - external border of the second rib.

Innervation - ventral rami of cervical nerves C7 and C8.

Action - flexes the neck laterally; elevates the second rib during forced inspiration

Add the Middle Scalene.

Origin - Posterior tubercles of transverse processes of C5-C7 vertebrae.

Insertion - superior surface of the first rib’ posterior to the groove for subclavian artery.

Innervation - ventral rami of cervical spinal nerves.

Action - flexes the neck laterally; elevates the first rib during forced inspiration.

Add the Anterior Scalene.

Origin - Transverse processes of C3-C6

Insertion - 1st Rib

Innervation - cervical spinal nerves C4-C6

Action - Flex the head.

The roots of the Branchial Plexus emerge from the cervical spine and travel between the anterior and middle scalene muscles as they begin to form the rest of the brachial plexus. This is a clinically relevant area for the administration of anesthetic when performing surgery on the upper limb

The roof of the Posterior Triangle is formed by the deep fascia which covers the space between the trapezius and sternocleidomastoid muscles. The roof is covered by skin, superficial fascia, the platysma muscle, and superficial veins and nerves.

Add the Subclavian Artery

Add the Transverse Cervical Artery

Add the Subscapular Artery

Add the Occipital Artery

Add the Internal Jugular Vein and the External Jugular Vein and identify the point at which the External Jugular Vein branches from the Jugular Vein

Add the Retromandibular Vein

Review the roots of the Brachial Plexus (ventral rami of C5-T1) lies in the posterior triangle immediately posterior to the anterior scalene and anterior to the middle scalene

Add the Spinal Accessory Nerve (CN XI) divides the posterior triangle into nearly equal superior and inferior parts. The superior part contains only the lesser occipital nerve while the inferior part contains many important nerves. Spinal Accessory nerve is a motor nerve comprised of spinal and cranial roots

text goes hereThe Lesser Occipital Nerve (C2) – ascends a short distance along the posterior border of the sternocleidomastoid muscle before dividing into several branches that supply the skin of the neck and scalp. (This nerve is not visable on this cadaver)

text goes hereThe Greater Auricular Nerve (C2-C3) – runs vertically over the sternocleidomastoid muscle toward the parotid gland (which lies anterior to the ear). It supplies branches to the skin of the neck, posterior aspect of the auricle of the ear, and an area extending from the mandible to the mastoid process. (This nerve is not visable on this cadaver)

The Transverse Cervical Nerve (C2-C3) – runs transversely across the middle of the sternocleidomastoid muscle to supply skin over the anterior triangle of the neck. (This nerve is not visable on this cadaver)

The Supraclavicular Nerves (C3-C4) – arise as a single trunk and divides into three main branches. They supply skin over the anterior aspect of the chest and shoulder

The Phrenic Nerve (C3, C4, C5) – NOT part of the cervical plexus but derived from the ventral rami of C3, C4, C5. It runs on the anterior aspect of the anterior scalene muscle to enter the thoracic cavity where it ultimately innervates the diaphragm muscle (Mnemonic: C3, C4, C5 keeps the diaphragm alive)

The Long Thoracic Nerve which arises from C5, C6, C7 cervical ventral rami passes posterior to the trunks of the brachial plexus and lies on the superficial side of the serratus anterior muscle (part of the medial wall of the axilla). This nerve also innervates the serratus anterior. This nerve was previously identified. Find it on the cadaver

The Thoracodorsal Nerve branches directly off of the posterior cord of the brachial plexus, descends along the posterior wall of the axilla, and innervates the large latissimus dorsi muscle. The latissimus dorsi muscle is a powerful adductor, extender, and medial rotator of the arm at the glenohumeral joint, therefore, injury to the thoracodorsal nerve will result in significant weakness of those motions. This nerve was previously identified. Find it on the cadaver.

The Intercostal Brachial Nerve is a branch of the second intercostal nerve. It leaves the thoracic wall, spans the axilla to reach the medial side of the arm where it joins with the medial brachial cutaneous nerve to provide cutaneous sensory innervation. Injury to this nerve during the operative. Procedure can lead to persistent postoperative pain or numbness in the region. (This nerve is not visable on this cadaver)