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Lecture 18 Anatomy .احمد فاضل د

The Root of the Neck

The root of the neck can be defined as the 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 understandingthe root of the neck . It

is deeply placedand it descends almost vertically from the vertebral column

to the 1st rib.

Important Relations

Anteriorly: Related to the carotid arteries, the vagus nerve, the internal jugular vein,

and the deep cervicallymph nodes. The transverse cervical and suprascapular arteries

and the prevertebral layer of deep cervical fascia bind the phrenic nerve to the

muscle.

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Posteriorly: Related to the pleura, the origin of the brachialplexus, and the second

part of the subclavian artery. The scalenusmedius muscle lies behind thescalenus

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 cervicalplexus, the roots of the

brachial plexus, and the thirdpart of the subclavian artery

Scalenus Medius

The scalenusmedius lies behind the scalenus anteriorand extends from the transverse

process of the atlas andthe transverse processes of the next five cervical vertebrae

downward and laterally to be inserted into theupper surface of the 1st rib behind the

groove for the subclavian

artery. The muscle lies behind the roots of the brachialplexus and the subclavian

artery.

The Thoracic Duct

The thoracic duct begins in the abdomen at the upper endof the cisterna chyli. It

enters the thorax through the aortic opening in the diaphragm and ascendsthrough the

posterior mediastinum, inclining gradually tothe left. On reaching the superior

mediastinum, it is foundpassing upward along the left margin of the esophagus. Atthe

root of the neck, it continues to ascend along the left margin of the esophagus until it

reaches the level of thetransverse process of the seventh cervical vertebra. Here, it

bends laterally behind the carotid sheath. Onreaching the medial border of the

scalenus anterior, it turnsdownward and drains into the beginning of the left

brachiocephalicvein. It may, however, end in the terminal partof the subclavian or

internal jugular veins.

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Main Nerves of the Neck

Cervical Plexus

The cervical plexus is formed by the anterior rami of thefirst four cervical nerves.

The rami are joined by connectingbranches, which form loops that lie in front of the

originsof the levator scapulae and the scalenusmedius muscles. The plexus is covered

in front by the prevertebrallayer of deep cervical fascia and is related to theinternal

jugular vein within the carotid sheath. The cervicalplexus supplies the skin and the

muscles of the head, theneck, and the shoulders.

Branches

■■Cutaneous branches

The lesser occipital nerve (C2), which supplies the backof the scalp and the auricle

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The greater auricular nerve (C2 and 3), which suppliesthe skin over the angle of the

mandibleThetransverse cervical nerve (C2 and 3), which suppliesthe skin over the

front of the neck

The supraclavicular nerves (C3 and 4). The medial, andintermediate, and lateral

branches supply the skinover the shoulder region.

■■Muscular branches to the neck muscles. Prevertebralmuscles,

sternocleidomastoid (proprioceptive, C2 and3), levator scapulae (C3 and 4), and

trapezius (proprioceptive,C3 and 4). A branch from C1 joins the hypoglossalnerve.

Some of these C1 fibers later leave the hypoglossal as the descending branch, which

unites withthe descending cervical nerve (C2 and 3), to form the ansacervicalis.

The first, second, and third cervical nerve fibers within the ansacervicalis supply

theomohyoid, sternohyoid, and sternothyroid muscles.Other C1 fibers within the

hypoglossal nerve leave it asthe nerve to the thyrohyoid and geniohyoid.

■■Muscular branch to the diaphragm. Phrenic nerve

Phrenic Nerve

The phrenic nerve arises in the neck from the 3rd, 4th, and5th cervical nerves of the

cervical plexus. It runs verticallydownward across the front of the scalenus anterior

muscleand enters the thorax by passing in front of the subclavianartery.The phrenic

nerve is the only motor nerve supply to thediaphragm. It also sends sensory branches

to the pericardium,the mediastinal parietal pleura, and the pleura andperitoneum

covering the upper and lower surfaces of thecentral part of the diaphragm.

Brachial Plexus

The brachial plexus is formed in the posterior triangle ofthe 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 formthe upper trunk, the root of C7 continues as the middletrunk, and the

roots of C8 and T1 unite to form the lowertrunk.

Each trunk then divides into anterior and posteriordivisions. The anterior divisions

of the upper and middletrunks unite to form the lateral cord, the anterior divisionof

the lower trunk continues as the medial cord, and theposterior divisions of all three

trunks join to form the posteriorcord.

The roots of the brachial plexus enter the base of theneck between the scalenus

anterior and the scalenusmedius muscles. The trunks and divisionscross the posterior

triangle of the neck, and the cordsbecome arranged around the axillary artery in the

axilla. Here, the brachial plexus and the axillaryartery and vein are enclosed in the

axillary sheath.

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The Autonomic Nervous System inthe Head and Neck

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Sympathetic Part

Cervical Part of the Sympathetic Trunk

The cervical part of the sympathetic trunk extends upwardto the base of the skull and

below to the neck of the 1st rib,where it becomes continuous with the thoracic part of

thesympathetic trunk. It lies directly behind the internal andcommon carotid arteries

(i.e., medial to the vagus) and isembedded in deep fascia between the carotid sheath

andthe prevertebral layer of deep fascia.The sympathetic trunk possesses three

ganglia: the superior,middle, and inferior cervical ganglia.

Superior Cervical Ganglion

The superior cervical ganglion lies immediately below theskull.

Branches

1. The internal carotid nerve, consisting of postganglionicfibers, accompanies

the internal carotid artery intothe carotid canal in the temporal bone. It divides

intobranches around the artery to form the internal carotidplexus.

2. Gray rami communicantesto the upper four anteriorrami of the cervical

nerves

3. Arterial branches to the common and external carotidarteries. These branches

form a plexus around the arteriesand are distributed along the branches of the

externalcarotid artery.

4. Cranial nerve branches, which join the 9th, 10th, and12th cranial nerves

5. Pharyngeal branches, which unite with the pharyngealbranches of the

glossopharyngeal and vagus nerves toform the pharyngeal plexus

6. The superior cardiac branch, which descends in the neck and ends in the

cardiac plexus in the thorax

Middle Cervical Ganglion

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

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2. Thyroid branches, which pass along the inferior thyroidartery to the thyroid

gland

3. The middle cardiac branch, which descends in the neckand ends in the

cardiac plexus in the thorax

Inferior Cervical Ganglion

The inferior cervical ganglion in most people is fused withthe first thoracic ganglion

to form the stellate ganglion.It lies in the interval between the transverse process

ofthe 7th cervical vertebra and the neck of the 1st rib, behind the vertebral artery.

Branches

1. Gray rami communicantesto the anterior rami of the7th and 8th cervical

nerves

2. Arterial branches to the subclavian and vertebral arteries

3. The inferior cardiac branch, which descends to join thecardiac plexus in the

thorax

The part of the sympathetic trunk connecting the middlecervical ganglion to the

inferior or stellate ganglion is representedby two or more nerve bundles. The most

anteriorbundle crosses in front of the first part of the subclavianartery and then turns

upward behind it. This anterior bundleis referred to as the ansasubclavia..

Parasympathetic Part

The cranial portion of the craniosacral outflow of theparasympathetic part of the

autonomic nervous system islocated in the nuclei of the oculomotor (3rd), facial

(7th),glossopharyngeal (9th), and vagus (10th) cranial nerves.The parasympathetic

nucleus of the oculomotor nerve

is called the Edinger-Westphal nucleus; those of the facialnerve the

lacrimatoryand the superior salivary nuclei;that of the glossopharyngeal nerve the

inferior salivarynucleus; and that of the vagus nerve the dorsal nucleusof the

vagus. The axons of these connector nerve cells aremyelinated preganglionic fibers

that emerge from the brainwithin the cranial nerves.

These preganglionic fibers synapse in peripheral ganglialocated close to the viscera

they innervate. The cranial parasympatheticganglia are the ciliary, the

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pterygopalatine,the submandibular, and the otic. In certain locations, theganglion

cells are placed in nerve plexuses, such as the cardiacplexus, the pulmonary plexus,

the myenteric plexus(Auerbach’s plexus), and the mucosal plexus

(Meissner’splexus). The last two plexuses are found in the gastrointestinaltract. The

postganglionic fibers are nonmyelinated,and they are short in length.

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