Root+of+the+Neck

toc =**Objectives**=

**General Goal**

 * 1. Describe the root of the neck, including its boundaries, contents, and important anatomical relationships.**

The root of the neck is the junction area between the thorax and the neck. It opens into, and is the cervical side of, the superior thoracic aperture, through which pass all structures going from the head to the thorax and vice versa.

The root of the neck is bound laterally by the first rib, anteriorly by the manubrium, and posteriorly by the T1 vertebrae. From anterior to posterior, the major contents include the clavicle, subclavian vein, anterior scalene muscle with phrenic nerve (C3-C5), subclavian artery, brachial plexus, and middle scalene muscle.

The anterior and middle scalene attach to rib 1 and flank the brachial plexus as it comes out (Note: Posterior scalene attaches to rib 2).

**Specific Goals**

 * 1A. Describe the relationship between the scalene muscles and the major vessels and nerves in the root of the neck?**

The anterior scalene muscle attaches to rib 1 and passes anterior to the subclavian artery. As the subclavian artery goes over the first rib to become the axillary artery, the anterior scalene muscle dives the subclavian artery into 3 parts: 1st part medial to anterior scalene, 2nd part posterior to anterior scalene, and 3rd part lateral to anterior scalene. Anterior to the anterior scalene muscle, the subclavian vein passes over the 1st rib, and is parallel to the subclavian artery. The subclavian vein unites with the internal jugular vein to form the brachiocephalic vein.

Between anterior scalene and middle scalene muscles, the roots and trunks of the brachial plexus pass through on their way to the upper limb. The phrenic nerve is formed on the lateral borders of the anterior scalene muscle and passes inferiorly on the anterior surface of anterior scalene and posterior to the inferior jugular veins and sternocleidomastoid muscle (SCM).


 * 1B. What is the relationship among subclavian vein, clavicle, and first rib?**

The axillary vein continues as the subclavian vein begins at the lateral border of the 1st rib and ends when it unites with the internal jugular vein, posterior to the medial end of the clavicle, to form the brachiocephalic vein.

The subclavian vein passes over the 1st rib parallel to the subclavian artery but separated from it by the anterior scalene muscle. It usually receives a tributary from the external jugular vein.


 * 2A. Describe the branches of the subclavian artery.**

The subclavian artery is divided into three parts by the anterior scalene muscle: the medial 1st, posterior 2nd, and lateral 3rd parts.

The first part medial to the anterior scalene muscle contains three major branches: the vertebral artery, internal thoracic artery, and thyrocervical trunk. The thyrocervical trunk gives off the inferior thyroid artery, ascending cervical artery, suprascapular artery, and either the transverse cervical artery or superficial cervical artery. If a transverse cervical artery exists, it will give off a superficial branch and the dorsal scapular artery (the deep branch).

The second posterior part gives off the costocervical trunk which gives off the deep cervical artery and supreme intercostal artery.

If the transverse cervical artery does not exist and there is a superficial cervical artery instead, the dorsal scapular artery arises from the third lateral part of the subclavian artery directly.


 * 2B. What is the course of the vertebral artery?**

The vertebral artery passes through the transverse foramen of the C1 through C6 cervical vertebrae as it ascends the neck. It typically does not enter the transverse foramen of the C7 vertebrae; this is important in surgery where a surgeon can compress the vertebral artery against the C7 transverse process.

The vertebral artery supplies blood to radicular arteries and segmental medullary arteries. Segmental medullary arteries also supply the spinal cord. It also supplies the dorsal root ganglion and spinal nerves. Eventually the vertebral artery ends up in the brain.


 * 2C. What is the thyrocervical trunk and what are its branches?**

The thyrocervical trunk is a branch off of the medial first part of the subclavian vein. It gives off four branches: inferior thyroid, ascending cervical, suprascapular, and either the transverse cervical artery or superficial cervical artery. If the transverse cervical artery exists, it gives off a superficial cervical artery and the dorsal scapular artery.

The inferior thyroid artery supplies the thyroid. It is the largest branch of the thyrocervical trunk and the primary visceral artery in the neck.

The ascending cervical artery sometimes comes off the inferior thyroid and heads superiorly along the anterior side of the vertebral disks, anteriomedial to the course of the vertebral artery. It supplies an anulus fibrosis, deep neck muscles (longus colli muscles), intervertebral disks, dorsal root ganglion, spinal nerves, and the spinal cord.

The suprascapular artery ends up on the posterior side of the scapula, passing through the scapular notch and supplying supraspinatus and infraspinatus. It sometimes may arise directly from the subclavian artery instead of off the thyrocervical trunk.

The transverse cervical artery gives rise to a superficial branch and dorsal scapular artery. The superficial branch goes superiorly; the dorsal scapular artery goes inferiorly along the medial border of the scapula to supply latissimus dorsi, levator scapulae, rhomboids, and trapezius. The transverse cervical artery only exists in about 25% of people.


 * 2D. What is the costocervical trunk and what are its branches?**

The costocervical trunk arises from the subclavian artery from the posterior 2nd part and heads posteriorly. It gives off two branches: deep cervical artery, and the supreme intercostal artery.

The deep cervical artery parallels the ascending cervical artery and supplies cervical vertebrae, spinal nervers, erector spinae muscles and posterior deep cervical muscles (rotators cervicis and interspinalis cervis muscles).


 * 2E. What are the transverse cervical, dorsal scapular, and suprascapular arteries?**

The transverse cervical, dorsal scapular, and suprascapular arteries represent important anatomical variations.

The transverse cervical artery or superficial cervical artery branches off of the thyrocervical trunk of the medial first part of the subclavian artery. The dorsal scapular artery can arise from either the transverse cervical artery or from the lateral third part of the subclavian artery directly.

In approximately 75% of people, there is no true transverse cervical artery. Instead, a superficial cervical artery arises from the thyrocervical trunk on the medial first part of the subclavian artery directly and the dorsal scapular artery arises independently from the third part of the subclavian artery.

However, in 25% of people, a transverse cervical artery arises from the thyrocervical trunk of the medial first part of the subclavian artery and gives off two branches: a superficial branch and a deep branch which is the dorsal scapular artery. The superficial cervical artery that 75% of people have basically functions as the superficial branch of the transverse cervical artery.

The suprascapular artery branches off of the thyrocervical trunk of the medial first part of the subclavian artery. However, it may also arise directly off of the subclavian artery.


 * 3. Describe the nerves found in the root of the neck.**

The vagus nerve descends in the carotid sheeth and gives rise to the recurrent laryngeal nerve which loops underneath the right subclavian or arch of the aorta and goes into the groove between the trachea and esophagus, posterior to the thyroid gland to innervate the larynx inferior to the vocal cords.

The phrenic nerve runs from C3, C4 and C5 along the anterior scalene muscle, deep to the carotid sheath.

The cervical portion of the sympathetic trunk contains three ganglion: Superior cervical, Middle cervical, and Inferior cervical. The inferior cervical (C7) and first thoracic (T1) ganglia usually fuse to form the stellate ganglia. The superior cervical ganglion is found around the C1-C2 vertebral level, middle cervical ganglion at C6 vertebral level, and the stellate ganglion at the C7-T1 vertebral level. The superior cervical ganglion supplies structures in the head and is the largest of the three ganglia.


 * 4. Describe the thyroid gland, its vasculature, and innervation.**

The thyroid gland is located at C6-T1 and has two lateral lobes, an isthmus and sometimes a pyramidal lobe. The pyramidal lobe is a remnant on the path of the thyroglossal duct from the foramen cecum of the tongue from which the thyroid gland originally migrated. It receives blood from superior thyroid from external carotid artery and the inferior thyroid artery from thyrocervical trunk. In 10% of the population, a thyroid ima artery from either the brachiocephalic trunk, aortic arch, right common carotid artery, subclavian artery or internal thoracic artery. It is drained by superior and middle thyroid veins to the internal jugular vein, and the inferior thyroid vein to the brachiocephalic vein. The arteries of the thyroid gland receive sympathetic innervation (vasomotor -NOT secretomotor). It has no parasympathetic innervation with its secretory functions under the control of hormones (TSH) from the anterior pituitary.


 * 5A. Describe the major groups of lymph nodes found in the neck.**

Superfical cervical lymph nodes are found along the external and anterior jugular veins and drain toward deep cervical lymph nodes.

__Superficial Cervical Nodes__ Occipital Mastoid Pre-auricular & parotid Submandibular Submental

__Deep Cervical Nodes__ Collection nodes along Internal jugular vein Inferior deep cervical nodes

Nodes along transverse cervical artery are know as "sentinel nodes" to which cancer metastases tend to spread


 * 5B. How is lymph returned to the venous system in the root of the neck?**

Lymph from the head and neck drain from superficial lymph nodes to deep lymph nodes to jugular trunks. Subclavian trunk which drains the upper limbs joints the jugular trunks to form the lymph trunk. On the left side, the thoracic duct draining everything below the diaphragm joins with the right jugular trunk as it becomes the left lymph trunk. On both sides, the lymph trunks will then drain back into the left and right subclavian veins just lateral to the junctions with the left and right internal jugular veins, returning the lymph into venous circulation.

The bronchomediastinal trunks, which drain the thorax, drain independently to the left and right subclavian veins directly, near where the lymph trunks drain.