Deep structures of the neck: Root of the neck

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Introduction0:00–0:22

The neck has both superficial and deep structures. But before you stick your neck out and try to guess what the deep structures are, we will just tell you.
The deep structures consist of paravertebral muscles and the viscera extending through the superior thoracic aperture at the root of the neck.When looking at the root of the neck specifically, it joins the neck and thorax, and acts like a passageway for neurovascular structures going from the thorax to the head or upper limb and vice versa.

The root of the neck0:22–1:16

It’s located on the cervical side of the superior thoracic aperture, which is formed laterally by the first pair of ribs and their costal cartilages, anteriorly by the manubrium of the sternum and posteriorly by the body of T1 vertebra.
The root of the neck contains neurovascular structures like the brachiocephalic trunk and the subclavian arteries, as well as veins such as the external and anterior jugular veins and the subclavian vein, and nerves such as the vagus nerve, phrenic nerves and the sympathetic trunks.

Arteries1:16–6:13

Let’s look at the arteries first. The brachiocephalic trunk is the largest branch of the aorta which arises in the midline from the beginning of the arch of aorta, posterior to the sternal manubrium.
It’s covered anteriorly by the right sternohyoid and sternothyroid muscles and passes superolaterally to the right and bifurcates posterior to the sternoclavicular joint into the right common carotid artery and right subclavian artery.
Now, the right and left subclavian arteries supply each upper limb and also send branches to the neck and brain. Now, while the right subclavian artery arises from the brachiocephalic trunk, the left subclavian artery arises from the arch of the aorta directly, about 1 centimeter distal to the origin of the left common carotid artery.
Although the two subclavian arteries have different origins, they have the same course in the neck. So, they start posterior to the sternoclavicular joints on either side, and they ascend through the superior thoracic aperture and enter the root of the neck.
Here, they arch superolaterally, reaching an apex as they pass posterior to the anterior scalene muscles. Then they begin to descend until they disappear posterior to the middle of the clavicles.
When they cross the outer margin of the first ribs, their name changes and they become the axillary arteries. Now, each subclavian artery has three parts which are described relative to the anterior scalene muscle.
So, the first part is medial to the anterior scalene, the second part is posterior to the muscle and the third part is lateral to the anterior scalene.
The first part of the artery gives three branches: the vertebral artery, the internal thoracic artery and the thyrocervical trunk.
The second part gives the costocervical trunk and the third part gives the dorsal scapular artery. The vertebral artery ascends in the neck and passes through the foramina transversaria of C1-C6 vertebrae.
Then, it enters the cranial cavity through the foramen magnum, also known as “the big hole in the occipital bone” to its friends.
Here, the vertebral artery supplies the medulla and spinal cord, parts of the cerebellum and the dura of the posterior cranial fossa.
The internal thoracic artery arises from the anteroinferior aspect of the first part of the subclavian artery and passes inferomedially into the thorax, and goes on to supply the anterior thoracic wall.
The thyrocervical trunk arises from the anterosuperior aspect of the first part of the subclavian artery, near the medial border of the anterior scalene muscle, and it has four branches: the inferior thyroid artery, the suprascapular artery, the ascending cervical artery and the transverse cervical artery.
The inferior thyroid artery supplies the larynx, trachea, esophagus, thyroid and parathyroid glands and the adjacent muscles.
The ascending cervical artery supplies the lateral muscles of the upper neck. The suprascapular artery passes through the posterior triangle then posterior to the clavicle to supply the supraspinatus and infraspinatus.
Finally the cervicodorsal trunk or the transverse cervical artery passes through the posterior triangle and supplies the trapezius muscle.
Next, the costocervical trunk arises from the posterior aspect of the second part of the subclavian artery behind the anterior scalene, and it passes posterosuperiorly to divide into the superior intercostal and deep cervical arteries which supply the first two intercostal spaces and the posterior deep cervical muscles, respectively.
Finally, the dorsal scapular artery typically branches off of the third part of the subclavian artery. However, sometimes the dorsal scapular artery arises as a deep branch of the transverse cervical artery.
Regardless of its origin, it supplies the levator scapulae and rhomboids. So far so good!
Take a quick break and try to recognize the branches of the subclavian artery. Next, let’s take a look at the veins in the root of the neck.

Quiz6:13–6:27

Veins6:27–7:50

There are two large veins that terminate in the root of neck: the external jugular vein which mostly drains blood from the scalp and face, and the anterior jugular vein which arises near the hyoid from the union of the superficial submandibular veins, and drains blood from the anterior aspect of the neck.
The anterior jugular vein descends into the root of the neck where it drains into the external jugular vein or the subclavian vein.
Now, the subclavian vein is a continuation of the axillary vein, that begins at the lateral border of the first rib. It passes over the first rib anterior to the scalene tubercle and parallel to the subclavian artery from which is separated by the anterior scalene muscle.
The subclavian vein has only one tributary which is the external jugular vein, and ends when it joins with the internal jugular vein to form the brachiocephalic vein.
This union is called either the right or left venous angle, which is located posterior to the medial end of the clavicle.
The left venous angle is where the thoracic duct drains lymph, and the right venous angle is where the right lymphatic duct drains lymph.Finally, there are three major pairs of nerves in the root of the neck : vagus nerves, phrenic nerves and sympathetic trunks.

Nerves7:50–13:03

Now, the vagus nerves exit from the jugular foramen and then each nerve passes inferiorly in the neck within the posterior part of the carotid sheath in the angle between the internal jugular vein and the common carotid artery.
The right vagus nerve passes anterior to the first part of the subclavian artery and posterior to the brachiocephalic vein and to the sternoclavicular joint to enter the thorax.
The left vagus nerve descends between the left common carotid artery and the left subclavian artery and posterior to the sternoclavicular joint to enter the thorax.
In the inferior part of the neck, each vagus nerve gives a recurrent laryngeal nerve which have essentially the same distribution, however, they loop around different structures and at different levels on the two sides.
So, the right recurrent laryngeal nerve loops inferior to the right subclavian artery at the level of T1-T2 vertebrae, and the left recurrent laryngeal nerve loops inferior to the arch of the aorta at the level of T4-T5 vertebrae.
After looping, both nerves ascend superiorly to the posteromedial aspect of the thyroid gland where they ascend in the tracheoesophageal groove, supplying both trachea and esophagus as well as all the intrinsic muscles of the larynx, except the cricothyroid.
The phrenic nerves are formed at the lateral borders of the anterior scalene muscles, mainly from the C4 nerve with contributions from C3 and C5 nerves.
Each phrenic nerve forms at the superior part of the lateral border of the anterior scalene muscle at the level of the superior border of the thyroid cartilage and they descend obliquely with the internal jugular vein across the anterior scalene, deep to the prevertebral layer of deep cervical fascia and the transverse cervical and suprascapular arteries.
The left phrenic nerve crosses anterior to the first part of the subclavian artery and the right phrenic nerve lies on the anterior scalene muscle and crosses anterior to the second part of the subclavian artery.
On both sides, they run posterior to the subclavian vein and anterior to the internal thoracic artery as it enters the thorax.
These nerves provide the sole motor supply to the diaphragm as well as sensation to its central part and also they supply the mediastinal pleura and pericardium.Finally, the root of the neck contains the cervical portion of the sympathetic trunks which are located anterolateral to the vertebral column and extends superiorly to the level of C1 vertebra or the cranial base.
They include three cervical sympathetic ganglia: superior, middle and inferior, which receive presynaptic fibers transmitted to the trunk by the superior thoracic spinal nerves inferiorly and their associated white rami communicantes.
Then, they ascend through the sympathetic trunk to these three ganglia. In the cervical sympathetic ganglia, the thoracic presynaptic fibers synapse with the postsynaptic neuron, which then send fibers and sympathetic innervation to the cervical spinal nerves, via gray rami communicantes, to the thoracic viscera, via cardiopulmonary splanchnic nerves, and to the head and viscera of the neck via cephalic arterial branches such as the external carotid and vertebral arteries.
Now, the superior cervical ganglion is located at the level of C1 and C2 vertebrae and sends sympathetic innervation to the cranial cavity via branches travelling with arteries such as the carotids.
The middle cervical ganglion is the smallest of the three ganglia and is occasionally absent. When it’s present, it’s located on the anterior aspect of the inferior thyroid artery at the level of the cricoid cartilage and the transverse process of C6 vertebra, and sends sympathetic innervation to organs like the heart and thyroid gland.
Finally, the inferior cervical ganglion fuses with the first thoracic ganglion in 80% of individuals and forms the cervicothoracic ganglion or stellate ganglion, which is a star-shaped ganglion located anterior to the transverse process of C7 vertebra, just superior to the neck of the first rib on each side and posterior to the origin of the vertebral artery.
This sends sympathetic innervation to C7 and C8 spinal nerves via grey rami communicantes, as well as nerves to the heart and trachea.
Ok so, before we wrap up, let’s take a quick break and see if you can recognize the three major pairs of nerves in the root of neck.All right, as a quick recap.

Quiz13:03–13:21

Review13:21–14:56

The root of the neck is a junctional area between the neck and thorax, and is the gateway for neurovascular structures going from the thorax to the head or upper limb and vice versa.
It is formed laterally by the first pair of ribs and their costal cartilages, anteriorly by the manubrium of the sternum and posteriorly by the body of T1 vertebra.
Arteries passing through the root of the neck are the brachiocephalic trunk and subclavian arteries. Each subclavian artery has three parts where the first part of the artery gives three branches: the vertebral artery, the internal thoracic artery and the thyrocervical trunk, the second part of the artery gives the costocervical trunk and the third part of the artery typically gives the dorsal scapular artery.
Veins in the root of the neck are represented by the external and anterior jugular veins which eventually drain into the subclavian vein.
The subclavian vein then combines with the internal jugular vein to form the brachiocephalic vein and the venous angles where lymphatic drainage occurs.
Major nerves in the root of neck are the vagus nerves and its branching of the recurrent laryngeal nerve, phrenic nerves supplying the diaphragm, and sympathetic trunks which include superior, middle and inferior cervical ganglion to distribute sympathetic innervation to the cranium, neck, thorax and upper limb.