The neck, as a major conduit between the head, trunk and limbs, contains the vasculature, nerves, viscera, and vocalization (larynx) that ensure their function and are thus essential to life. The complexity and intricate nature of the anatomy is obvious. However, by initially focussing on the osteology, it is easier to understand the organization of the neck and the systems that rely on its integrity.

The temporal bone, zygomatic arches, occipital bone, mandible, cervical vertebrae, scapula clavicles, manubrium, and hyoid bone form the skeleton of the neck.

• Enclosed within the vertebral canal is the spinal cord and the meninges
• Foramen transversarium: Transverse processes which contain the vertebral vessels*
• C1: Atlas – Carrier of the Skull

• Lacks a spinous process and body
• Consists of two lateral masses connected by anterior and posterior arches with concave articular facets receiving the occipital condyles superiorly
• Anteriorly, possesses a facet for articulating with the Dens on the anterior arch
• Superiorly, posterior to the condylar fossa, it possesses a groove where the vertebral artery, vein and c1 travel
• Transverse Processes can be palpated posterior to the ramus of the mandible

• C2: Axis – Often considered the body of C1

• Dens: Peglike odontoid process projecting superiorly from body

• C3, C4, C5, & C6 Characteristics:

• Vertebral body

1. small and longer from side to side than anteroposteriorly
2. superior surface is concave forming the uncinate processes laterally
3. inferior surface is convex
4. can be used as a landmark for hyoid (C3), thyroid cartilage and bifurcation of the common carotid artery (C4), cricoid cartilage (C6)

• Vertebral foramen is large and triangular

• C7: Vertebrae Prominens

• Long spinous process visible through skin
• Large transverse processes
• *Foramina transversaria are small and only transmits vertebral vein

• Hyoid Bone

• Mobile, C-Shaped bone lying in the anterior part of the neck at the level of C3 in the angle between the mandible and the thyroid cartilage.
• Suspended by muscles that connect to the mandible, styloid processes, thyroid cartilage, manubrium of the sternum, and the scapulae
• Does not articulate with any other bone – Suspended from the styloid processes of the temporal bones by the stylohyoid ligaments and is firmly bound to the thyroid cartilage by the thyrohyoid membrane
• Functionally serves as an attachment for the deep investing fascia, anterior neck muscles and keeps the airway open

*The preferred site of tracheostomy is at tracheal cartilages 2-4 (below cricoid cartilage and isthmus of the thyroid gland).

• Atlanto-occipital joint: joint between atlas (vertebra C1) and occipital bone; movements - flexion - extension of the neck (nodding the head in "yes" movement).
• Atlanto-axial joint: joint between atlas (C1) and axis (C2); movement: rotation of atlas on axis (shaking head in "no" movement)
• Ligaments of joint - stabilize joints and protect medulla and spinal cord; some prevent excessive movement; some are extensions of ligaments of spinal column

1. Cruciate (cross) ligament - composed of

• Transverse ligament of atlas: transverse band within vertebral canal which is attached to inner side of atlas; holds dens of axis against inner aspect of anterior arch of atlas
• Superior and inferior bands: upper and lower extensions from transverse ligament of atlas to occipital bone superiorly and to body of the axis inferiorly.

1. Alar ligament: extends laterally from dens to occipital bone; prevents excessive rotation of head.
2. Membrana Tectoria: extension of posterior longitudinal ligament of spinal column - extends from axis to occipital bone, posterior to cruciate ligament.
3. Anterior atlanto-occipital membrane:= extension of anterior longitudinal ligament - extends from atlas to occipital bone

Using the osteological scaffolding of the neck, it is essential to develop an understanding of the fascial layers. Fascia of the neck forms compartments and communicating tubes which serve to organize the vascular and visceral structures as well as nerves and vocalization contained within its boundaries. Superficial and Deep Cervical fascial planes as well as the fascial spaces created by the layers determine the direction an infection in the neck may be spread and deserve serious attention by all clinicians. By consulting the illustrations of fascial layers, it is possible to not only to gain an appreciation for their orientation and relationship to one other, but embryological development can be better understood and the triangles of the neck virtually form themselves. In addition, consideration of compartmentalization significantly contributes to mastering the reading of CT scans and MR images and other crossectional representations.

Capitalizing on fascia’s inherent ability to provide organization, we can use the Deep Cervical Fascial compartments to understanding the placement of structures in the neck. Initially we address the infrahyoid portion (below the hyoid) as having 4 tubes enclosed by a greater outer tube.

• Contains the:

1. Common and internal carotid arteries
2. Internal Jugular vein
3. Vagus nerve (CN X)
4. Deep cervical lymph nodes
5. Carotid sinus nerve
6. Sympathetic fibers

• Clinical: Sheath is extremely strong which prevents easy compression. Therefore a problem in the carotid sheath can crush the internal jugular vein and vagus nerve

1. Superior nuchal line of occipital bone
2. Spinous processes of cervical vertebrae
3. Mastoid processes of temporal bones
4. Zygomatic arches
5. Inferior border of mandible
6. Hyoid bone

• Inferiorly it attaches to

1. Manubrium
2. Clavicles
3. Acromion

• Continuous posteriorly with periosteum covering C7 spinous process and ligamentum nuchae – an extension of the supraspinous ligament that forms a median fibrous septum between the muscles of the two sides of the neck
• Just above the sternum this layer is split to contain the anterior jugular veins in a suprasternal space

• Surrounds infrahyoid (strap) muscles: Sternohyoid, Sternothyroid, Omohyoid, Thyrohyoid
• Thickens to form a pulley through which the intermediate tendon of the digastric muscle passes, suspending the hyoid bone
• Tethers the omohyoid muscle, redirecting the course of the muscle between the two bellies
• Fused with the Superficial layer of fascia that lies on the Deep surface of SCM

• Attached superiorly to the cricoid cartilage, thyroid cartilage, and hyoid bone
• Attached posteriorly to the (Pre)Vertebral Fascia

• Blends laterally with the carotid sheath and inferiorly with the fibrous pericardium
• Blends posteriorly and superiorly with pharyngeal fascia of the pharynx
• Continuous with Investing Fascia at lateral borders of infrahyoid muscles

• Thin layer on the pharynx itself
• Often broken down into Retropharyngeal, Lateral Pharyngeal and Buccopharyngeal components as it posteriorly to anteriorly envelops the pharynx
• Retropharyngeal fascia is considered continuous below (T2) with the visceral fascia on the esophagus(Retrovisceral/Retroesophageal Fascia)
• Separates the muscular wall of the pharynx from certain potential spaces that largely surround it.
• Other Components of Visceral Fascia discussed in detail in Suprahyoid section

• Alar fascia is the anterior subdivision of prevertebral fascia that bridges between the transverse processes. It blends with the (retro)Visceral fascia (posterior fascia of the esophagus) at the level of T2 vertebral body. This seals inferiorly the (retro)Pharyngeal space. It runs from the base of the skull to the superior mediastinum

• The posterior subdivision of prevertebral fascia is simply termed "prevertebral" and attaches to the transverse processes and the body of the vertebrae at the midline, and covers the prevertebral muscles (longissimus capitus/cervicus, longus coli).

• Scalene Fascia: A derivative of the Vertebral Layer of Fascia on the scalene muscles.

• Between this fascia and the anterior scalene muscle is the phrenic nerve.
• Deep to the fascia, in a triangle between the anterior and middle scalenes, there is contained the root of the brachial plexus and subclavian artery.

• Clinical: If the anterior or middle scalene mm’s are swollen due to trauma or infection, the brachial plexus and/or the subclavian artery can be compressed and thus cause thoracic outlet syndrome with either vascualr or neurological symptoms

• Can be infected directly by anterior perforations of the esophagus or indirectly by spread from the retrovisceral portion, around the sides of the esophagus and thyroid gland between the levels of the inferior thyroid artery and the oblique line of the thyroid cartilage. Both pretracheal and retrovisceral spaces descend into the superior mediastinum.

• Key to an understanding downward spread of infections of the head and neck: commonly regarded as a route through which infections of the mouth and throat reach the mediastinum. It can break through the posterior wall of the space through the alar fascia, and can enter Danger Space 4, between the two lamellae of the prevertebral layer of fascia (extends from the base of the skull to the level of the diaphragm).

• Fatal hemorrhage could potentially result from an extension of a retropharyngeal abscess to the deep vessels of the neck

• Majority of cases arising from the internal carotid artery rather than from the jugular vein: the vein is more often occluded by the infectious process than it is eroded to the point of hemorrhage. A sudden enlargement of a retropharyngeal mass may indicate erosion of a large vessel and that in such a case aspiration of the mass before its incision may prevent fatal hemorrhage.

• Important pathway by which infections orginating from various locations in the head and the upper portion of the neck reach the mediastinum.
• The retrovisceral space may also be infected directly from posterior perforations of the esophagus or by infections of the deep cervical nodes lying adjacent to it.

• Infection can communicate from posterior wall of the oropharynx and oral cavity to the thorax by traveling from the Retropharyngeal Space, and passing downward to the Retrovisceral space (which begins below the pharynx). It can then pierce thru the weak alar fascia - into Danger Space #4
• "Dangerous" because an infection can easily travel to the thoracic cage and mediastinum, i.e., mediastinitis. Abscess in the mediastinum could go anteriorly to the pericardial area and could affect the manubrium, sternum, etc..

• Clinical: It can be involved in any neck infection because it is made of three layers: Investing, Pretracheal and Prevertebral Fascia.

• Infections tend to be localized within the cervical region (between hyoid and root of the neck) because the sheath is closely adherent to vessels
• Infection usually arises from thrombosis of the internal jugular vein or from infection of those deep cervical lymph nodes that lie within the sheath

• Thrombosis of the jugular vein from a deep infection of the neck is probably not due to direct infection of the carotid sheath, but rather to the fact that infectious material follows tributaries of the internal jugular vein to reach the sheath.
• Drug use (Heroin) usually use carotid route to obtain a fast high. A result can be abscess of the carotid sheath presenting in a patient who is groggy with a weak pulse (bradycardia) and low blood pressure due to the compression of the carotid sinus and irritation of the vagus nerve.

1. Fascial Layers less complicated: Superficial, Prevertebral, Buccopharygeal

No pretracheal layer

2. Fascial Spaces more complicated:

1. Masseteric fascia: following the external surface of the masseter to the zygomatic arch
2. Another portion following the internal deep surface of the medial pterygoid muscle to the pterygoid plate

1. Behind the angle of the jaw and anterior to the SCM, this layer passes upward toward the zygomatic arch

1. Parotid fascia: splits to form a capsule about the parotid gland before attaching to the zygomatic arch.

The spaces may be divided into three categories:

1. Blind or Intrafascial spaces: formed by splitting of fascial layers
2. Intercommunicating spaces: surrounding the pharynx and lying between fascial laminae and the pharyngeal walls
3. Blind "spaces": potential only, within the pharyngeal wall deep to the buccopharyngeal fascia.

1. formed by a splitting of the prevertebral layer of cervical fascia
2. extending from the base of the skull into the thorax

The other intrafascial spaces related to the upper part of the neck are all formed by a splitting of the superficial layer of cervical fascia to attach to the skull, as well as to surround glands and muscles

• Potential spaces do not communicate with each other: infections within them can spread only through rupture of their walls.
• The only one of these four spaces containing any appreciable quantity of loose connective tissue is that associated with the muscles of mastication.

Space of the Body of the Mandible

1. Limited anteriorly by superfical investing fascia and the attachment of the anterior belly of the digastric
2. Limited posteriorly by superfical investing fascia and the attachment of the medial pterygoid to the jaw
3. Inferiorly closed by the continuity of the fascial layers
4. Superiorly closed by the attachment of fascial layers to the inferior border of the body of the mandible.
5. Formed by the attachment of the superficial layer of fascia to both the outer and inner surfaces of the body of the mandible

• attachment to the outer surface is at the lower border of the mandible
• attachment to the inner surface can be elevated from the mandible up to the origin of the mylohyoid muscle

1. Clinical: An infection here may remain localized, may discharge into the mouth, or may spread to the masticator space.

Submandibular/Submaxillary Space

1. The outer layer of the capsule: the continuation upward of the main portion of the superficial layer of the cervical fascia, is strong
2. the inner layer is thinner and is perforated by the duct of the gland

1. Clinical:

1. infections arising in the region of the gland generally break inward

• Since these structures lie between the fascial layers on the outer surface of the masseter and the inner surface of the medial pterygoid, the loose connective tissue and fat about them forms the potential space

1. Its largest part is medial to the ramus of the mandible, between this and the medial pterygoid, and medial and anterior to the lower portion of the insertion of the temporal muscle.
2. Posteriorly, the fascial walls of this space come together behind the ramus of the mandible.
3. Anteriorly, a part of the masseteric fascia attaches to the mandible in front of the masseter muscle and to the insertion of the temporal muscle along the anterior border of the ramus,
4. Anteriorly, it is limited by another part passes in front of the ramus, across the outer surface of the buccal fat pad, to attach to the maxilla and the buccinator fascia below that
5. Superiorly, it is limited deep to the temporal muscle by the origin of this muscle from the skull,
6. Superficially, it is limited by the muscle's origin from the temporal fascia.
7. Deeply, anterior to the lateral pterygoid plate it extends into the pterygopalatine fossa.
8. Lies largely among the muscles of mastication. Those bordering the space are enclosed by thin fascial layers that separate them from the fat pad and subdivide the masticator space into compartments that do not freely communicate with each other.
9. It is traversed particularly by the mandibular nerve and the maxillary (internal maxillary) vessels, and
10. Largely filled by the buccal fat pad and its extensions posteriorly, upward, and medially
11. Clinical

• Infections of the zygomatic or temporal bones may pass to the masticator space, and so may abscesses from the lower molar teeth
• Abscesses within this space may apparently point at the anterior aspect of the masseter muscle, either into the cheek or the mouth, or they may point posteriorly below the parotid gland.

Space of Parotid Gland

• Since they intervene between the intrafascial spaces and the mandible or pharynx, they are liable to infection from either of these sources by extension from them
• These spaces are most intimately related to the lymph nodes receiving the drainage from the nose, throat, and jaw, so that abscesses within them may form from breakdown of nodes secondarily infected from their regions of drainage.

• both above and below these muscles it opens medially into the retropharyngeal space

1. Anterosuperiorly extends to the Pterygomandibular raphe
2. Anteriorly is continuous with the submandibular (submaxillary portion) space
3. Clinical: Subject to infection from several sources

1. Considered to be the route by which infections of diverse origins may be transmitted. Infection generally does not pass directly into the lateral visceral space, but pushes the carotid bundle and passes to the highway-the retropharyngeal space-that in turn leads to the mediastinum.
2. Through its connection with the spaces about the tongue, it may receive and transmit to the retropharyngeal space infections originating here, as from the teeth;
3. similarly, it is adjacent to the submandibular gland, and infections in this gland may spread into the space;
4. Both the masticator space and the parotid gland border the lateral pharyngeal space, and infections within either of these that perforate deeply instead of superficially will necessarily invade the lateral pharyngeal space.
5. Tonsillar region of the pharynx is the medial wall of the lateral pharyngeal space, and infections originating about the tonsils may also involve this space.
6. Infections within the petrous portion of the temporal bone may rupture directly into the lateral pharyngeal space, and infection at the tip of the mastoid process may follow the mastoid groove and extend along the styloid and digastric muscles to this space

Submandibular Fascial Space

• Mylohyoid muscle, stretching across the floor of the mouth, divides the submandibular space into a portion above this muscle: Sublingual and a portion below: Submaxillary
• These two subdivisions can communicate by infection or injection along the free edge of the mylohyoid muscle and about the submandibular gland, which lies partly above and partly below the posterior portion of the mylohyoid

• Sublingual space

• Contains the sublingual gland, the duct for the submandibular gland, and the accessory submandibular gland, Lingual Nerve, and the hypoglossal nerve appearing deep
• Consist of the loose connective tissue lying between the muscles of the tongue and about the sublingual gland, the lingual and hypoglossal nerves, and a portion of the submandibular gland and its duct.

• Paired but the two sides communicate anteriorly
• Subdivided based upon their relationships to the genioglossus and geniohyoid muscles
• Clinical: Infection will pass down to the submandibular space or can pass directly through the mylohyoid muscle

• Submaxillary space is divided into subsidiary submental and submaxillary spaces by attachment of the superficial layer of fascia to the anterior belly of the digastric muscle,

• Submental space containing submental lymph nodes

• Corresponding to the triangle of the same name, lies medial to the anterior belly of the digastric

• Submaxillary space lateral and posterior to it

• Contains Submandibular Gland with its fascial covering, Facial Artery and Vein, Hypoglossal Nerve, Vena hypoglossi commitantes

• These spaces consist only of an easy line of cleavage between the fascia and the muscles, unless they are abnormally distended.
• The roots of the third, second, and first molars are all below the level of the mylohyoid. Infection of these teeth pass through the root, directly into the submaxillary space and then to the lateral pharyngeal space. Patient can present with problems in their airway. Never give a nerve block if there is an infection of the submandibular space. Infection can be passed by way of a needle tract infection to a deeper area of the body.

• The roots of the second and third molar teeth reach downward to the level of the attachment of the mylohyoid muscle, and usually below it, while most of those of the first molar teeth, and usually all of those anterior to this, are located above this level.

INTRAPHARYNGEAL SPACES

Since the pharyngeal constrictors are covered by the (bucco)pharyngeal fascia, a potential space theoretically exists between muscles and fascia. Infections here, like those within the visceral fascia lower in the neck, tend either to remain localized or to break through into the lateral pharyngeal and retropharyngeal spaces.

A common method used to assist in the understanding and locating different structures in the neck is to geometrically separate the neck into triangular components and noting the contents and their relationships.

The mastoid process located immediately posterior to the external ear (auricle) marks the superior attachment for the large sternocleidomastoid muscle as it passes to its attachment on the clavicle and sternum. This muscle separates the posterior triangle from the anterior triangle of the neck. It is best palpated by turning the head against pressure to one side and palpating the opposite side of the neck.

THE ANTERIOR TRIANGLE OF THE NECK

Using a lateral view of the neck we can easily identify the Borders of the anterior triangle of the neck:

• Midline of the neck from chin to manubrium
• Anterior border of the sternocleidomastoid
• Inferior border of the mandible

The Investing layer of deep cervical fascia anteriorly covers the anterior triangle of the neck and fuses with the opposite fascia in the midline.

Contains the Suprahyoid and the Infrahyoid muscles:

Origins, Insertions and Actions can be reviewed in the text.

The anterior triangle of the neck can be further subdivided into:

• Most noted for the presence of several submental lymph nodes which drain the floor of the oral cavity, tip of the tongue and lower lip
• Anterior jugular veins: Lying in the midline, running from the submental triangle, they pierce the deep fascia above manubrium. They pass between the posterior border of the sternocleidomastoid muscle and the upper border of the clavicle to drain into the external jugular veins in the posterior triangle of the neck.

• Submandibular (Digastric) Triangle: between the posterior and anterior bellies of the digastric muscle and inferior border of the mandible. Its floor is formed by the mylohyoid, hyoglossus and middle constrictor muscles.

• Continuous with the fossa for the parotid gland
• Mylohyoid muscle lyes superior to the anterior belly of the digastric

• Forms a sling passing from side to side from the internal surface of the mandible (mylohyoid line)
• Forms the floor of mouth: It is attached from the mylohyoid line to the superior aspect of body of hyoid bone and the midline raphé.

• Around the posterior edge of this muscle lies the submandibular salivary gland which occupies a significant part of the triangle

• Associated with the anterior belly of digastric, both are derived from the 1^st Branchial Arch and therefore share the same innervation: Mylohyoid Br. of the Inferior Alveolar N. of V3

• Hypoglossal nerve (CN XII) also passes into the triangle as it goes to the tongue

• Facial artery, arising from the external carotid, passes superiorly deep to the posterior belly of digastric and winds over the submandibular gland and "grooves" the inferior edge of the mandible to reach the face

• Posterior belly of the digastric:

• Comes from the medial surface of the mastoid process,
• Attaches to the anterior belly of digastric by the intermediate tendon which is tied down by a fascial sling to the body of the hyoid.
• Associated with the stylohyoid, both are derived from the 2nd Branchial Arch and therefore share the same innervation: Facial N. (CN VII)

• Muscular Triangle: between the superior belly of the omohyoid, lower anterior margin of the sternocleidomastoid and the median line of the neck.

Medially contains infrahyoid muscles.

• Sternohyoids: lying close to the midline

• Muscles pass from the posterior surface of the manubrium of the sternum to insert on the hyoid bone.

• Sternothyroids: immediately lateral

• Also pass from the posterior sternum but insert onto the thyroid cartilage of the larynx

• The superior belly of the omohyoid lies lateral to it

• Omohyoid:

• Splits both the anterior and posterior triangles
• Two bellies united by an intermediate tendon which is connected to the clavicle by a fascial sling

• Thyrohyoid: above the thyroid cartilage

• Completes the gap from thryoid cartilage to hyoid bone

• Innervated by fibers from C1 which have piggybacked onto the hypoglossal nerve (CN XII) and subsequently jump off that nerve to supply this muscle as well as the geniohyoid.
• Contains visceral structures of the neck including the thyroid gland, larynx, trachea and esophagus.

• Carotid Triangle between the posterior belly of the digastric, superior belly of the omohyoid and the anterior surface of the sternocleidomastoid muscle.

As the vascular area of the neck, it is most noted for the carotid sheath and its contents:

The Common Carotid Artery arises in the base of the neck from the brachiocephalic artery on the right side and directly from the arch of the aorta on the left side. It passes into the base of the neck through the thoracic inlet bounded by the sternum and first rib and ascends into the carotid triangle

• Medial to the artery is the esophagus and trachea
• Internal jugular vein lies lateral to it
• It can be compressed on the transverse process of C6 (the carotid tubercle).

• Bifurcation into the internal and external carotid arteries occurs at the level of the upper border of the thyroid cartilage/level of the hyoid bone (C3)

• Gives no branches in neck and simply ascends to the carotid canal to enter the base of the skull.
• Has the carotid sinus (baroreceptors associated with IX) at its beginning
• The carotid body is present at the bifurcation and has chemoreceptors.

• Lies posterolateral to the external carotid artery.
• Cranial nerve IX or glossopharyngeal nerve runs deep to the internal carotid artery and penetrates the lateral pharyngeal wall with the stylopharyngeus muscle. It is motor to this muscle and sensory to the mucosa of posterior 1/3 of tongue, mucosa of pharynx, palatine tonsil and soft palate.

• Main arterial supply to structures of the neck and superficial face
• Gives of several branches, some of which originate or pass through the carotid triangle.
• Lie inferior to (I), deep to (D) or superior to (S) the posterior belly of the digastric.

• The superior laryngeal artery supplying the inner aspect of the larynx
• The cricothyroid branch running with the external laryngeal nerve.
• The muscular branch to the sternocleidomastoid muscle.

Internal Jugular Vein collects blood from the brain, face and neck

• Usually the largest vein in the neck
• As a direct continuation of the sigmoid sinus, it begins after exiting the jugular foramen
• Passes inferiorly through the carotid triangle receiving many tributaries from surrounding structures.
• At the base of the neck it unites with the subclavian vein on either side to form right and left brachiocephalic veins which in turn forms the superior vena cava.
• Deep cervical lymph nodes lie along its course

The vagus has an extensive distribution as it conveys motor and sensory nerve fibers to structures in the neck, thorax and abdomen. It enters the neck by exiting the skull through the jugular foramen. In the carotid triangle it lies behind and between the carotid and jugular vessels. Several branches are present.

• The internal laryngeal branch which pierces the thyrohyoid membrane, is sensory to laryngeal mucosa above vocal cords and is involved in the coughing reflex.
• The external laryngeal branch which runs on the lateral aspect of the larynx to innervate the cricothyroid muscle which tenses vocal cords during vocalization.

• (upper branches) voluntary motor nerves to the muscles of palate (except for the tensor palati muscle which is innervated by V3), to the pharynx (except for the stylopharyngeus muscle ) and to the larynx.
• (lower branches) parasympathetic preganglionic fibers to the cervical, thoracic and abdominal regions
• sensory fibers with the inferior sensory ganglion lying in jugular fossa.
• sensory fibers to the skin of the external auditory canal with cell bodies lying in the superior sensory ganglion in the jugular fossa.

• Lying lateral to the internal jugular vein and the carotid sheath, the ansa cervicalis forms a loop of nerve fibers whose principal function is to supply motor innervation to the strap muscles (except the thyrohyoid) of the front of the neck.
• C1 hitchhikers travel with the Hypoglossal Nerve: some of these fibers leave the Hypoglossal nerve in the neck and descend down and join other nerves of anterior rami of C2 and C3 (inferior root) to innervate neck muscles
• Other fibers of C1 travel further with the Hypoglossal nerve and jump off to innervate the Thyrohyoid and Geniohyoid muscles
• Remember: Only hitch-hiking fibers from C1-C3 actually innervate neck muscles - not the Hypoglossal nerve itself
• Produce Sensory nerves: The great auricular nerve and transverse cervical nerves (anterior cutaneous nerve of neck) for C2 and C3 dermatomes.
• The cervical branch of cranial nerve VII (motor nerve) enters the platysma muscle on its deep surface near the angle of the mandible.

Sympathetic Trunk – Autonomic Nerve Fibers and Ganglia

• Lies posterior to the carotid sheath in the carotid triangle on the anterior aspect of longus coli..
• May occur as a single band or as web-like filaments passing upward and therefore may be difficult to differentiate from fascia of the sheath.
• Preganglionic fibers arise from the superior thoracic spinal nerves which leave the thorax through the inlet and travel to cervical structures
• 3 Cervical Sympathetic Ganglia:

• Wrapped around the posterior aspect of the vertebral artery
• May be fused with the thoracic ganglion to form the stellate ganglion
• Post-ganglionic fibers pass to C7, C8, heart, and vertebral plexus around the vertebral artery

• Anterior to the vertebral artery

• Post-ganglionic fibers pass to C5 &C6, heart and the thyroid gland

• Postganglionic fibers enter the cranial cavity and sends branches to the external carotid artery, c1-c4, and the cardiac plexus

THE POSTERIOR TRIANGLE OF THE NECK

Using a lateral view of the neck we can once again easily identify the Borders of the posterior triangle of the neck:

• Sternocleidomastoid anteriorly
• Trapezius posteriorly
• Clavicle inferiorly

1. Splenius capitis - ligamentum nuchae and upper thoracic spinous vertebrae to the mastoid process and occipital bone (draws head backward or to the respective side).

2. Levator scapulae - processes of C1-C4 to the superior aspect of the medial border of the scapula (elevates scapula).

3. Scalenus muscles

All muscles of the posterior triangle, whether boundary or floor muscles, are enclosed by separate subdivisions of the deep investing fascia of the neck.

The posterior triangle of the neck can be further subdivided into:

• Occipital triangle lying above the inferior belly of the omohyoid
• Supraclavicular (Omoclavicular) triangle inferior to this muscle.

BOUNDARIES OF THE OCCIPITAL TRIANGLE:

CONTENTS OF THE OCCIPITAL TRIANGLE:

The lower four cervical nerves (C5,C6,C7,C8) are found in the scalene gap (space between scalenus anterior and scalenus medius muscles) and they, along with the first thoracic nerve (T1), make up the brachial plexus. Cervical nerves C5, C6, join to form the superior (upper) trunk of the brachial plexus, and these nerves as well as part of the superior trunk are found in the occipital triangle. Branches from the roots of C5, C6, and C7, as well as from the superior trunk include:

1. Dorsal scapular nerve - from the root of C5, pierces scalenus medius, and continues caudally on the deep surface of levator scapulae. This nerve innervates levator scapulae, rhomboids and it is accompanied by the dorsal scapular artery.
2. Long thoracic nerve - from the roots of C5, C6, C7. Once formed, it passes posterior to the brachial plexus and then along the chest wall (close to the mid-axillary line) to innervate serratus anterior.
3. Superior trunk of the brachial plexus – Present in both triangles, this trunk will be discussed in detail in the next section

1. Suprascapular - through the suprascapular foramen to innervate supraspinatus and infraspinatus

2. Middle trunk of the brachial plexus - this trunk is the continuation of the anterior primary division of the 7th cervical nerve.
3. Lower trunk of the brachial plexus - this trunk is formed from the anterior primary division of the 8th cervical and 1st thoracic nerves.
4. Subclavian artery (3rd part) - the first part of the subclavian artery lies medial to scalenus anterior, the second part lies posterior to this muscle, and the third part lies lateral to the scalenus anterior. The thyrocervical trunk arises from the first part of the subclavian, and two of its several branches (transverse cervical, suprascapular), pass through both the supraclavicular and occipital triangles in route to their destinations. The transverse cervical supplies trapezius, subscapularis, levator scapulae and the rhomboids, while the suprascapular supplies supra and infraspinatus. Occasionally there are no branches from the third part of the subclavian. An exception is when the descending scapular (dorsal scapular) arises from the second or third part of the artery.
5. External Jugular Vein: Derived from the Following Overview of venous drainage in the head and neck.

1. Superficial Temporal and Maxillary veins unite to form Retromandibular vein.
2. Retromandibular vein divides at angle of mandible into Anterior and Posterior divisions.
3. Anterior division joins Facial Vein to form Common Facial vein which drains into Internal Jugular vein.
4. Posterior division joins Posterior Auricular vein to form External Jugular vein.
5. External Jugular vein descends across Sternocleidomastoid muscle to drain into Subclavian vein.
6. Anterior Jugular vein forms from small veins below mandible;descends to join Ext. Jugular vein above clavicle. After lying superficial to the sternocleidomastoid muscle, the external jugular vein descends to the anterior angle of the posterior triangle where it enters the subclavian vein.

An important landmark in this region is the scalenus anterior muscle which passes from the anterior tubercles of C3 - C6 to its attachment at the scalene tubercle on the first rib.

Using scalenous anterior as a landmark Subclavian Artery is divided into three main parts with several important branches:

• Vertebral artery - arises from its upper posterior surface

• passes into the foramen transversarium of C6 and ascends, winds behind the lateral mass of the atlas and enters the skull at the foramen magnum. It unites with the vertebral artery from the opposite side to form the basilar artery.
• important since its has branches that also supply the cervical spinal cord

• Internal thoracic artery - arises opposite the vertebral artery posterior to the subclavian vein

• Runs in the pleura and enters the thorax on the posterior aspect of the sternum
• supplies anterior intercostal branches (running between the ribs) and terminates as the musculophrenic artery which supplies the diaphragm and superior epigastric artery which runs in the anterior abdominal wall.

• Thyrocervical trunk - Lateral to the musculophrenic artery and superior, breaks into inferior thyroid artery and suprascapular artery.

• Inferior thyroid artery passes upwards and medially toward the inferior pole of the thyroid gland. Immediately anterior to it lies the carotid sheath and, somewhat more medially, the middle cervical ganglion of the sympathetic trunk. It anastomoses with the superior thyroid artery coming from the external carotid artery. It supplies the scalenus anterior and the longus colli muscles by its ascending cervical artery.

• Suprascapular artery passes laterally across the posterior triangle to the upper border of the scapula. This artery may arise from the third part of the subclavian and in this situation may separate the superior from the middle and inferior trunks of the brachial plexus.
• Transverse (or Superficial) Cervical along with the suprascapular a. initially passes anterior to scalenus anterior and clamp down the phrenic nerve as they run into the posterior triangle of the neck

• Costocervical artery: (on the left it generally arises from the first part) passes posteriorly over the apex of the lung to give 2 branches:

• Superior/Highest Intercostal artery to supply first two intercostal spaces with Posterior Intercostal arteries

• Deep Cervical Artery to deep musculature for the back of the neck.

• Dorsal scapular artery passes laterally through the brachial plexus and passing deep tot he levator scapulae it reaches the scapula and descends deep to the rhomboids with the dorsal scapular nerve.

THE ROOT OF THE NECK

• On the right, the brachiocephalic trunk divides into subclavian and common carotid arteries posterior to sternoclavicular joint.
• On the left, the left common carotid and left subclavian arteries ascend posterior to sternoclavicular joint.

• It lies inferior to the artery, within the arch formed by the artery over the apex of the lung.

• Branches of the 1st part of the subclavian artery (as previously discussed)

• Phrenic nerve:

• From the anterior rami of C3-5
• Is formed at the superior lateral portion of the scalenus anterior and courses to the medial border of this muscle.
• Is in the prevertebral fascia and is crossed anteriorly by the suprascapular and transverse cervical arteries.
• Is motor to the diaphragm, sensory to the parietal pleura and the peritoneum covering the diaphragm.

• Trachea and esophagus (cervical portions)

• From C6 to the superior aperture of the thorax (T1, rib1 and manubrium).
• They are invested in the visceral fascia along with the thyroid gland.

• This visceral column lies between the 2 carotid sheaths and anterior to the bodies of the vertebrae and the prevertebral fascia in the root of the neck.

• Triangle of the Vertebral Artery: an important triangle of clinical importance extending from the root of the neck

• scalenus anterior muscle
• longus colli muscle
• superior aspect of the subclavian artery

• (Pre)Vertebral Fascia surrounds this area. As it travels down the longus coli muscles it deviates laterally toward the "axillary fascia" in order to continue to cover the anterior and middle scalenes and the levator scapulae.

• Contents of the triangle of the vertebral artery:

• Vertebral artery (from the first division of the Subclavian artery) and vein ascend to the apex of triangle and enter the foramen transversarium of C6.

• The artery, besides aiding in cranial perfusion, provides blood supply to the spinal column at C3, C5 and C6. If there is a blockage due to trauma or atherosclerosis, then these spinal cord segments can potentially become ischemic and thus impact on the respective dermatomes

• Clinical:

• If there is a problem in the vertebral artery that prevents proper circulation, the patient will not necessarily experience light-headedness due to the compensatory mechanism of the anastamosing Circle of Willis. Instead, the symptoms to look for are Sensory depravation, paresthesis, and numbness or weakness in the aforementioned dermatomes: i.e., Hand, arm, and back
• If the vertebral arteries are bilaterally impaired, this would directly impinge on C3,C4 and C5 and thus the diaphragm would be affected. The patient would necessitate a respirator.
• Stellate Ganglion (Inferior Cervical Ganglion fusing with the Sympathetic may be overly stimulated by the nearby vertebral artery

• A little note on the embryonic development: The 4^th Aortic arch, forming the initial segment of the right subclavian artery, represents the most inferior arch on the Right side during embryonic development and thus is the only barrier that the recurrent laryngeal nerve needed to loop around. Consequently, during dissection of the lower neck, it is the only recurrent laryngeal nerve that you will see. However, on the left side, the 6th aortic arch was retained as the ductus arteriosus (later the arch of the aorta) and the left recurrent laryngeal nerve was forced to loop around it during development.

EXTRA STUFF FOR LATER!!!!!!!!

The Hyoglossus muscle runs from the greater horn of the hyoid bone and inserts into the tongue. Cranial nerve XII lies against its external surface and the lingual artery lies against its internal surface.

Thyroid gland:

• is formed by 2 lobes lying lateral to the larynx and the trachea. The lobes are connected by the isthmus at the level of tracheal cartilages 2-4.
• is overlapped by the sternothyroid muscles and related laterally to the carotid sheath.
• may have a pyramidal lobe (developmental origin in the tongue area).
• is vascularized by the superior and inferior thyroid arteries.

The recurrent laryngeal branches of the vagus nerves lie deep to thethyroid lobes near the posterior aspect of the trachea. These nerves arethus vulnerable in thyroid surgery.

4 parathyroid glands are associated with the posterior surfaceof the thyroid gland.