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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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