Chapter 25. Overview of the Neck

Big Picture

The cervical fascia consists of concentric layers of fascia that compartmentalize structures in the neck (Figure 25-1). These fascial layers are defined as the superficial fascia and the deep fascia, with sublayers within the deep fascia. The fascia of the neck can determine the direction in which infection in the neck may spread.

Superficial Cervical Fascia

The superficial cervical fascia is the subcutaneous layer of the skin in the neck. This thin layer contains the muscles of facial expression, including the platysma muscle in the neck. The cutaneous nerves, superficial vessels, and superficial lymph nodes course within the superior cervical fascia.

Deep Cervical Fascia

The deep cervical fascia is deep to the superficial fascia. The deep cervical fascia is condensed in various regions to form the following sublayers: the investing layer of the deep cervical fascia, the pretracheal fascia, the prevertebral fascia, and the carotid sheath. The function of the deep fascia is to provide containment of muscles and viscera in compartments, to enable structures to slide over each other, and to serve as a conduit for neurovascular bundles.

Investing Fascia

The investing fascia attaches as follows:

• Posteriorly to the nuchal ligament, completely encircling the neck and splitting to enclose the sternocleidomastoid and trapezius muscles.
• Superiorly to the hyoid bone and then splitting to enclose the submandibular gland.
• Along the mandible and splitting to enclose the parotid gland.
• Superiorly to the mastoid process, occipital bone, and zygomatic arch.
• Inferiorly along the acromion, scapular spine, clavicle, and manubrium.

Pretracheal Fascia

The pretracheal fascia forms a tubular sheath in the anterior part of the neck. The pretracheal fascia extends superiorly from the hyoid bone and inferiorly to the thorax, where it blends with the fibrous pericardium. The pretracheal fascia:

• Encloses the infrahyoid muscles.
• Encloses separately the thyroid gland, trachea, and esophagus.
• Blends laterally with the carotid sheath.
• Is contiguous inferiorly with the buccopharyngeal fascia of the pharynx.

Prevertebral Fascia

The prevertebral fascia forms a tubular sheath around the vertebral column and the prevertebral muscles, which are attached to the vertebral column. The prevertebral muscles are:

• Anteriorly, the longus colli and capitis muscles.
• Laterally, the anterior, middle, and posterior scalene muscles.
• Posteriorly, the deep cervical muscles.

The prevertebral fascia:

• Attaches superiorly from the base of the skull and inferiorly to the endothoracic fascia in the thorax.
• Extends laterally as the axillary sheath, which surrounds the axillary vessels and brachial plexus of nerves to the upper limb.
• Contains, within its connective tissue fibers, the cervical sympathetic trunk and ganglia.

Carotid Sheath

The carotid sheath also is a tubular fascial investment that extends superiorly between the cranial base and inferiorly to the root of the neck.

• The carotid sheath blends with the investing, pretracheal, and prevertebral layers of the deep cervical fascia.
• The carotid sheath contains the common and internal carotid arteries, internal jugular vein, and vagus nerve [cranial nerve (CN) X]. In addition, the carotid sheath contains deep cervical lymph nodes, sympathetic fibers, and the carotid sinus nerve.

Retropharyngeal Space

The retropharyngeal space is a potential space consisting of loose connective tissue between the prevertebral and the buccopharyngeal fascia.

Big Picture

The muscles of the neck are organized and grouped with the cervical fascia. The platysma muscle is located within the superficial fascia, and the sternocleidomastoid and trapezius muscles are located within the investing fascia (part of the deep cervical fascia). Vertebral muscles (prevertebral, scalene, and deep cervical) are located within the prevertebral fascia. The suprahyoid muscles are deep to the investing fascia, whereas the infrahyoid muscles are within the pretracheal fascia. The vertebral muscles are within the prevertebral fascia.

Platysma Muscle

The platysma muscle is the most superficial muscle of the neck. Unlike most skeletal muscles, the platysma is located in the superficial fascia (Figure 25-2A and B). The muscle extends superiorly from the inferior border of the mandible and inferiorly to the clavicle to the fascia of the anterior shoulder and thorax. The platysma muscle is a muscle of facial expression and therefore is innervated by the facial nerve (cervical branch of CN VII). Upon contraction, the platysma depresses the mandible and wrinkles the skin of neck.

Sternocleidomastoid and Trapezius Muscles

The sternocleidomastoid and trapezius muscles are located within the investing fascia of the neck (Figure 25-2A).

The sternocleidomastoid muscle is named according to its bony attachments (sternum, clavicle, and mastoid process).

• The sternocleidomastoid muscle creates the borders for both the anterior and the posterior triangles of the neck, and is innervated by the spinal accessory nerve (CN XI).
• This muscle flexes the neck, pulls the chin upward, and assists in elevating the rib cage during inspiration.

The trapezius muscle creates the anterior border of the posterior cervical triangle.

• The trapezius muscle attaches to the occipital bone, nuchal ligament, spinous processes of C7–T12, scapular spine, acromion, and the lateral part of the clavicle.
• The sternocleidomastoid muscle is innervated by CN XI.

Vertebral Muscles

The vertebral muscles are located between the prevertebral fascia and the cervical vertebrae, and are organized as described below.

Prevertebral Muscles

The longus colli and the longus capitis muscles are anterior muscles and course superiorly between the anterior aspects of the base of the skull and inferiorly between the cervical and upper thoracic vertebrae (Figure 25-2B). The longus colli and longus capitis muscles help stabilize the cervical vertebrae and flex the neck.

Scalene Muscles

The three scalene muscles are the anterior, middle, and posterior scalenes (Figure 25-2A and B).

• The scalene muscles attach to the cervical transverse processes and the first two ribs.
• These muscles elevate the ribs during breathing and laterally flex the neck.

The scalene muscles are homologous to the muscles of the body wall in that neurovascular structures course between the middle layer (middle scalene) and the deep layer (anterior scalene). As a result, both the cervical and brachial plexuses exit the vertebral column between the anterior and middle scalenes. In addition, the subclavian vein courses horizontally across the anterior scalene, whereas the phrenic nerve descends vertically on the anterior scalene.

Deep Cervical Muscles

The deep cervical muscles are located posteriorly on the neck and are part of the erector spinae and transversospinalis muscles. As such, they are innervated by the dorsal primary rami.

Suprahyoid Muscles

The suprahyoid muscles (i.e., digastric, stylohyoid, mylohyoid, and geniohyoid muscles) are located deep to the investing fascia of the deep cervical fascia (Figure 25-3A). These muscles raise the hyoid bone during swallowing because the mandible is stabilized.

• Digastric muscle. Has two bellies connected by a central tendon, which is attached to the hyoid bone. The posterior belly arises from the mastoid process, whereas the anterior belly arises from the mandible. Because of the two bellies, the digastric muscle can raise the hyoid bone or open the mouth. The digastric muscle originates embryologically from both the first and second pharyngeal arches; as such, it has a dual innervation [the anterior belly from the mandibular branch of the trigeminal nerve (CN V-3) and the posterior belly from CN VII].
• Stylohyoid muscle. Attaches from the styloid process, bifurcates around the posterior belly of the digastric muscle, and inserts on the hyoid bone. The stylohyoid muscle elevates the hyoid bone and is innervated by CN VII.
• Mylohyoid muscle. Located superiorly to the anterior belly of the digastric muscle and forms the floor of the mouth. The mylohyoid muscle elevates the floor of the mouth and is innervated by CN V-3.
• Geniohyoid muscle. Located superiorly to the mylohyoid muscle. The geniohyoid muscle elevates the hyoid bone and is innervated by the cervical plexus (C1) (not shown in the illustration).

Infrahyoid Muscles

The infrahyoid muscles include four pairs of muscles that are located within the muscular layer of the pretracheal fascia, inferior to the hyoid bone (hence the name) (Figure 25-3B). Each muscle is innervated by the ansa cervicalis from the cervical plexus (ventral rami C1–C3). Collectively, these muscles function to depress the hyoid bone and larynx during swallowing and speaking. They receive their names according to their attachments.

• Sternothyroid muscle. Sternum and thyroid cartilage.
• Sternohyoid muscle. Sternum and hyoid bone.
• Thyrohyoid muscle. Thyroid cartilage and hyoid bone.
• Omohyoid muscle. Has two bellies. The inferior belly attaches to the superior border of the scapula (“omo” for shoulder), and the superior belly attaches to the hyoid bone.

Big Picture

The subclavian and common carotid arteries and their associated branches provide most of the blood supply to the head and neck. The external and anterior jugular veins are the principal venous return for the neck, and the internal jugular vein provides venous return for the head.

Subclavian Artery

The subclavian arteries branch from the brachiocephalic artery on the right side and directly from the aortic arch on the left side (Figure 25-4A). The subclavian arteries course between the anterior and middle scalene muscles, where each becomes the axillary artery at the lateral edge of the first rib. Branches of the subclavian artery are as follows:

• Vertebral artery. Arises from the first part of the subclavian artery and ascends between the anterior scalene and the longus coli muscles, through the transverse foramina of C6 to C1. At the superior border of C1, the vertebral artery turns medially and crosses the posterior arch of C1, through the foramen magnum en route to the brain.
• Thyrocervical trunk. A short trunk that arises from the first part of the subclavian artery. Branches of the thyrocervical trunk are the suprascapular, transverse cervical, and inferior thyroid arteries.

Common Carotid Artery

The common carotid artery branches from the brachiocephalic artery on the right side and directly from the aortic arch on the left side. The common carotid artery ascends within the carotid sheath, along with the internal jugular vein and the vagus nerve (Figure 25-4A). The common carotid artery bifurcates at the upper border of the thyroid cartilage into an internal and an external carotid artery.

Internal Carotid Artery

The internal carotid artery gives off no branches in the neck, but within the skull it provides vascular supply to the anterior and middle regions of the brain, the orbit and the scalp.

External Carotid Artery

The external carotid artery supplies the neck and face through the following branches:

• Superior thyroid artery. Arises at the level of the hyoid bone and supplies the larynx and the thyroid gland.
• Lingual artery. Courses deep to the hyoglossus muscle, becoming the principal blood supply to the tongue.
• Facial artery. Ascends deep to the posterior belly of the digastric and stylohyoid muscles and the submandibular gland, where the facial artery hooks around the mandible along the anterior border of the masseter muscle. The facial artery contributes to the blood supply to the face.
• Ascending pharyngeal artery. Arises from the posterior surface of the external carotid artery and ascends to provide vascular supply to the pharynx and the palatine tonsils.
• Occipital artery. Courses posteriorly to the apex of the posterior triangle and supplies the occipital region of the scalp.
• Posterior auricular artery. Arises from the posterior surface of the external carotid artery and supplies the scalp posterior to the ear.
• Maxillary artery. Arises from the external carotid artery, posterior to the mandibular neck and supplies the deep structures of the face such as the infratemporal fossa.
• Superficial temporal artery. Arises as a terminal branch of the external carotid artery within the parotid gland and courses superficial to the zygomatic arch supplying the temporal region.

External Jugular Vein

The external jugular vein is forward at the angle of the mandible via the joining of the posterior auricular and posterior branch of the retromandibular veins (Figure 25-4B). The external jugular vein descends vertically down the neck within the superficial fascia, deep to the platysma muscle. After crossing the sternocleidomastoid muscle, the external jugular vein pierces the deep investing fascia posterior to the clavicular head and enters the subclavian vein.

• The posterior auricular vein drains the scalp behind and above the ear.
• The retromandibular vein is formed by the superficial temporal and maxillary veins within the parotid gland. The retromandibular vein divides into anterior and posterior divisions. The anterior division joins the facial vein to form the common facial vein. The posterior division contributes to the external jugular vein.

Internal Jugular Vein

The internal jugular vein originates at the jugular foramen by the union of the sigmoid and inferior petrosal sinuses and serves as the principal drainage of the skull, brain, superficial face, and parts of the neck. After exiting the skull via the jugular foramen, along with the glossopharyngeal, vagus, and accessory nerves (CNN IX, X, and XI, respectively), the internal jugular vein traverses the neck within the carotid sheath. The internal jugular vein joins with the subclavian vein to form the brachiocephalic vein. Tributaries include the facial, lingual, pharyngeal, and occipital veins, and the superior and middle thyroid veins. The right internal jugular vein lacks valves where as the left has one valve.

Big Picture

The cervical plexus of nerves is responsible for much of the sensory and motor innervation of the neck. CNN VII, IX, X, XI, and XII also play an important role. In addition, sympathetic innervation of the neck and head is via the cervical sympathetic trunk.

Cervical Plexus

The cervical plexus of nerves arises from the ventral rami of cervical nerves C1 to C4 and exits the vertebral column between the anterior and posterior scalene muscles. Branches of the cervical plexus are as follows (Figure 25-5A):

• Cutaneous (sensory) branches. Pierce the prevertebral fascia at the central region of the posterior border of the sternocleidomastoid muscle serving various regions of the skin of the neck. The cutaneous branches of the cervical plexus are as follows:
  • Lesser occipital nerve (C2). Innervates the skin over the lower, lateral region of the scalp.
  • Great auricular nerve (C2–C3). Innervates the skin over the parotid gland and angle of the jaw (this is the only area of the face not supplied by CN V); also contributes some cutaneous sensation to the external ear.
  • Transverse cervical nerve (C2–C3). Innervates the skin over the anterior part of the neck.
  • Supraclavicular nerve (C3–C4). Innervates the skin over the lower portion of the neck, upper part of the chest, and the shoulder.
• Motor nerves. The deep branches of the cervical plexus innervate muscles. The fibers from C1 travel briefly with CN XII and innervate the thyrohyoid and geniohyoid muscles. Fibers from C1 form the superior root of the ansa cervicalis. Fibers from C2 and C3 join to form the inferior root of the ansa cervicalis, where it lies anterior to the internal jugular vein and passes upward to join the superior root, forming a loop (ansa). Most of the motor nerves from the cervical plexus branch from the ansa cervicalis, supplying the infrahyoid muscles (sternothyroid, sternohyoid, and omohyoid). The cervical plexus also gives rise to the phrenic nerve.
  • Phrenic nerve (C3–C5). Courses vertically along the anterior scalene muscle between the subclavian artery and the subclavian vein en route to innervate the diaphragm. (“C3–C5, keep the diaphragm alive” is a pneumonic that is used to remember the spinal nerve levels of the phrenic nerve.)
  • The cervical plexus also provides motor nerves to other cervical muscles, including the scalenes, the longus colli, and the longus capitis.

Cranial Nerves in the Neck

The following cranial nerves travel through the neck (Figure 25-5B and C).

• Trigeminal nerve (CN V). CN V courses through the submandibular triangle to innervate the mylohyoid and the anterior digastric muscles.
• Facial nerve (CN VII). CN VII exits the skull, via the stylomastoid foramen, and provides branchial motor innervation to muscles of facial expression including the platysma muscle. In addition, branches within the oral cavity provide visceral motor (parasympathetic) innervation to the submandibular gland.
• Glossopharyngeal nerve (CN IX). CN IX exits the skull with CNN X and XI, via the jugular foramen, and provides visceral sensory innervation to the carotid sinus (baroreceptor) and carotid body (chemoreceptor) monitoring blood pressure.
• Vagus nerve (CN X). CN X exits the skull with CN IX and CN XI, via the jugular foramen, and descends within the carotid sheath, deep to the carotid artery and internal jugular vein. The vagus nerve contains both motor and sensory neurons supplying the gut tube (as far as the transverse colon), which includes the pharynx and larynx for swallowing and phonation, as well as sensory innervation from this same region. Important branches of CN X in the neck include the superior and recurrent laryngeal nerves. In addition, CN X provides visceral sensory innervation from the carotid body (chemoreceptor), monitoring blood pressure.
• Spinal accessory nerve (CN XI). CN XI exits the jugular foramen with CN IX and CN X, providing motor innervation to the sternocleidomastoid and trapezius muscles.
• Hypoglossal nerve (CN XII). CN XII exits the skull via the hypoglossal canal and courses into the submandibular triangle, providing somatic motor innervation to the tongue muscles (except the palatoglossus muscle).

Sympathetic Nerves of the Neck

The sympathetic trunk (chain) ascends from the thorax into the cervical region, within the prevertebral fascia along the longus colli and longus capitis muscles (Figure 25-5C). The sympathetic trunk in the cervical region receives only gray rami communicantes (no white rami). The sympathetic trunk innervates the sweat and sebaceous glands, blood vessels, and the errector pili, dilator pupillae, and superior tarsal muscles.

The sympathetic trunk gives rise to the following three cervical ganglia:

• Inferior cervical ganglion. Fuses with the first thoracic paravertebral ganglion to become the cervicothoracic (stellate) ganglion at the level of rib 1. The inferior cervical ganglion gives rise to the inferior cervical cardiac nerves.
• Middle cervical ganglion. Lies at the C6 vertebral level and gives rise to the middle cervical cardiac nerves.
• Superior cervical ganglion. Lies anterior to the C1–C2 transverse processes, between the internal carotid artery and the longus capitis muscle. The superior cervical ganglion contains cell bodies of postganglionic sympathetic fibers en route to the head and gives rise to the internal and external carotid plexuses and the superior cervical cardiac nerves.