1. The Root of the neck

2. The Root of the neck
The Root of the Neck can be defined as area of the neck immediately above the inlet into the thorax.
Muscles of the Root of the Neck
Scalenus Anterior Muscle
The scalenus anterior muscle is a key muscle in understanding the root of the neck .It is deeply placed and it descends almost vertically from the vertebral column to the 1st rib.

4. Important Relations
Anteriorly: Related to the carotid arteries, the vagus nerve, the internal jugular vein and the deep cervical lymph nodes. The transverse cervical and suprascapular arteries and the prevertebral of deep cervical fascia bind the phrenic nerve to the muscle.
Posteriorly :Related to the pleura, the origin of the brachial plexus, and the second part of the subclavian artery. The scalenus medius muscle lies behind the scalenus anterior muscle.
Medially :Related to the vertebral artery and vein and the sympathetic trunk. On the left side, the medial border is related to the thoracic duct.
Laterally: Related to the emerging branches of the cervical plexus, the roots of the brachial plexus, and the third part of the subclavian artery .

5. Scalenus Medius The scalenus medius lies behind the scalenus anterior and extends from the transverse process of the atlas and the transverse processes of the next five cervical vertebrae downward and laterally to be inserted into the upper surface of the 1st rib behind the groove for the subclavian artery. The muscle lies behind the roots of the brachial plexus and the subclavian artery.

7. The Thoracic Duct
The thoracic duct begins in the abdomen at the upper end of the cisterna chyli. It enters the thorax through the aortic opening in the diaphragm and ascends through the posterior mediastinum, inclining gradually to the left. On reaching the superior mediastinum, it is found passing upward along the left margin of the esophagus. At the root of the neck, it continues to ascend along the left margin of the esophagus until it reaches the level of the transverse process of the seventh cervical vertebra. Here, it bends laterally behind the carotid sheath. On reaching the medial border of the scalenus anterior, it turns downward and drains into the beginning of the left brachiocephalic vein. It may, however, end in the terminal part of the subclavian or internal jugular veins.

10. Main Nerves of the Neck Cervical Plexus The cervical plexus is fanned by the anterior rami of the first four cervical nerves. The rami are joined by connecting branches, which form loops that lie in front of the origins of the levator scapulae and the scalenus medius muscles. The plexus is covered in front by the prevertebral layer of deep cervical fascia and is related to the internal jugular vein within the carotid sheath. The cervical plexus supplies the skin and the muscles of the head, the neck, and the shoulders.

13. Branches Cutaneous branches
The lesser occipital nerve (C2), which supplies the back of the scalp and the auricle
The greater auricular nerve (C2 and 3): which supplies the skin over the angle of the mandible
The transverse cervical nerve (C2 and 3): which supplies the skin over the front of the neck
The supraclavicular nerves (C3 and 4): The medial ,and intermediate, and lateral branches supply the skin over the shoulder region.

15. Muscular branches to the neck muscles: Prevertebral muscles, sternocleidomastoid (proprioceptive, C2 and 3), levator scapulae (C3 and 4), and trapezius (proprioceptive, C3 and 4). A branch from C1 joins the hypoglossal nerve. Some of these Cl fibers later leave the hypoglossal as the descending branch, which unites with the descending cervical nerve (C2 and 3), to form the ansa cervicalis. The first, second, and third cervical nerve fibers within the ansa cervicalis supply the omohyoid, stemohyoid, and stemothyroid muscles. Other Cl fibers within the hypoglossal nerve leave it as the nerve to the thyrohyoid and geniohyoid .

18. Muscular branch to the diaphragm
Muscular branch to the diaphragm. Phrenic nerve Phrenic Nerve The phrenic nerve arises in the neck from the 3rd, 4th, and 5th cervical nerves of the cervical plexus. It runs vertically downward across the front of the scalenus anterior muscle and enters the thorax by passing in front of the subclavian artery .The phrenic nerve is the only motor nerve supply to the diaphragm. It also sends sensory branches to the pericardium, the mediastinal parietal pleura, and the pleura and peritoneum covering the upper and lower surfaces of the central part of the diaphragm.

21. Brachial Plexus The brachial plexus is formed in the posterior triangle of the neck by the union of the anterior rami of the 5th, 6th, 7th, and 8th cervical and the first thoracic spinal nerves. This plexus is divided into roots, trunks, divisions, and cords. The roots of C5 and 6 unite to form the upper trunk, the root of C7 continues as the middle trunk, and the roots ofC8 and T1 unite to form the lower trunk.

23. Each trunk then divides into anterior and posterior divisions
Each trunk then divides into anterior and posterior divisions. The anterior divisions of the upper and middle trunks unite to form the lateral cord, the anterior division of the lower trunk continues as the medial cord, and the posterior divisions of all three trunks join to form the posterior cord. The roots of the brachial plexus enter the base of the neck between the scalenus anterior and the scalenus medius muscles. The trunks and divisions cross the posterior triangle of the neck, and the cords become arranged around the axillary artery in the axilla. Here, the brachial plexus and the axillary artery and vein are enclosed in the axillary sheath.

25. The Autonomic Nervous System in the Head and Neck
Cervical Part of the Sympathetic Trunk
The cervical part of the sympathetic trunk extends upward to the base of the skull and below to the neck of the 1 st rib, where it becomes continuous with the thoracic part of the sympathetic trunk. It lies directly behind the internal and common carotid arteries (i.e., medial to the vagus) and is embedded in deep fascia between the carotid sheath and the prevertebral layer of deep fascia. The sympathetic trunk possesses three ganglia: the superior, middle, and inferior cervical ganglia.

27. The superior cervical ganglion lies immediately below the skull
The superior cervical ganglion lies immediately below the skull. Branches : 1. The internal carotid nerve, consisting of postganglionic fibers, accompanies the internal carotid artery into the carotid canal in the temporal bone. It divides into branches around the artery to form the internal carotid plexus. 2. Gray rami communicantes to the upper four anterior rami of the cervical nerves

28. 3. Arterial branches to the common and external carotid arteries
3. Arterial branches to the common and external carotid arteries. These branches form a plexus around the arteries and are distributed along the branches of the external carotid artery.
4. Cranial nerve branches, which join the 9th, 1Oth, and 12th cranial nerves
5. Pharyngeal branches, which unite with the pharyngeal branches of the glossopharyngeal and vagus nerves to form the pharyngeal plexus
6. The superior cardiac branch, which descends in the neck and ends in the cardiac plexus in the thorax

29. The middle cervical ganglion lies at the level of the cricoids cartilage.
Branches :
1. Gray rami communicantes to the anterior rami of the 5th and 6th cervical nerves
2. Thyroid branches, which pass along the inferior thyroid artery to the thyroid gland
3. The middle cardiac branch, which descends in the neck and ends in the cardiac plexus in the thorax

30. The inferior cervical ganglion in most people is fused with the first thoracic ganglion to form the stellate ganglion. It lies in the interval between the transverse process of the 7th cervical vertebra and the neck of the 1st rib, behind the vertebral artery. Branches : 1 Gray rami communicantes to the anterior rami of the 7th and 8th cervical nerves 2. Arterial branches to the subclavian and vertebral arteries 3. The inferior cardiac branch, which descends to join the cardiac plexus in the thorax

31. The part of the sympathetic trunk connecting the middle cervical ganglion to the inferior or stellate ganglion is represented by two or more nerve bundles .the most anterior bundle crosses in front of the first part of the subclavian artery and then turns upward behind it. This anterior bundle is referred to as the ansa subclavia..

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