The skull is the skeleton of the head, which encloses the brain and its coverings as well as the 12 cranial nerves connected to the brain; houses the organs of special senses (sight, hearing, taste, and smell); and surrounds the openings into the digestive and respiratory tracts. The cervical spine, consisting of seven cervical vertebrae, furnishes stability and support for the head, permits motion of the head and neck, and provides protection and housing for the cervical spinal cord and nerve roots as well as the vertebral artery (Figs. 16.1.1 and 16.1.2). The cervical spine is convex anteriorly. Anatomy of the head and neck is presented in detail in major anatomic textbooks (1,2,3,4,5,6).

Several important bony and cartilaginous structures can be palpated as one examines the head and neck. Beginning anteriorly, the horseshoe-shaped hyoid bone can be palpated in the crease of the neck superior to the thyroid cartilage at the level of the C3 vertebral body. Inferior to the hyoid bone in the midline of the neck is the thyroid cartilage. The superior notch can be palpated as well as the bulging central region, commonly referred to as the “Adam’s apple.” The thyroid cartilage lies at the level of the C4 and C5 vertebral bodies. The cricoid cartilage lies inferior to the thyroid cartilage at the level of the C6 vertebral body. It forms a complete ring, which is narrower anteriorly and considerably wider posteriorly. The cricothyroid membrane can be palpated between the thyroid and cricoid cartilages. Inferior to the cricoid cartilage is the first tracheal ring. The carotid tubercle lies about 2.5 cm lateral to the cricoid cartilage. This is the small anterior tubercle on the transverse process of the C6 vertebra and is covered by overlying muscles. The common carotid artery runs adjacent to the tubercle, and locating this tubercle is frequently used as a landmark for approaching the inferior cervical (stellate) sympathetic ganglion. The transverse process of the atlas (C1) can be palpated inferior to the ear between the angle of the mandible and the styloid process of the temporal bone.

On the lateral aspect of the skull, about 4 cm superior to the midpoint of the zygomatic arch, is the pterion. This is an H-shaped formation of sutures that unite the frontal, parietal, sphenoid, and temporal bones. The pterion is important clinically because it overlies the anterior branches of the middle meningeal artery, and a blow to this vulnerable area may rupture the underlying vessels. Posterior landmarks begin with the occipital bone (occiput). On the occipital bone one can palpate the external occipital protuberance (inion) on the midline and the superior nuchal line extending laterally from the external occipital protuberance. These structures mark the line of separation between the neck inferiorly and the head superiorly. At the lateral end of the superior nuchal line, the rounded mastoid process of the temporal bone can be palpated (Fig. 16.1.3). Beginning at the external occipital protuberance and proceeding inferiorly, the spinous processes of the cervical vertebrae can be palpated along the midline of the neck. The midline of the neck is indented due to the presence of the nuchal ligament lying immediately over the spinous processes and the laterally located paraspinal muscles and the overlying trapezius muscle. The first cervical spinous process that can be palpated is C2 and the rest can be palpated sequentially to C7. The C7 spinous process, at the base of the neck, is the longest of the cervical spinous processes and serves as an important landmark for the end of the neck and the beginning of the thorax. Moving laterally from the spinous process of C2, the zygapophyseal joints of the cervical vertebrae, lying deep to the trapezius muscle, can be palpated sequentially as one proceeds inferiorly until the articulation between C7 and T1 is reached.

All seven cervical vertebrae are easily identified by the presence of a transverse foramen in each transverse process. These foramina transmit the vertebral artery and accompanying sympathetic nerve plexus. Cervical vertebrae C3-C7 share common anatomic features. Their relatively small cell body is wider side to side than front to back. The vertebral foramen is large in comparison to its size in other regions of the spine in order to accommodate the enlarged cervical spinal cord. The superior margin of the body curves up as an uncus (lip). The uncus articulates with beveled reciprocal facets on the inferior surface of the vertebral body above to form the uncovertebral joints (of Luschka). The pedicles are short and, along with the lateral aspect of the body, serve as the origin for the broad transverse processes. The superior and inferior vertebral notches are shallow, thus creating a very narrow intervertebral foramen. The superior and inferior articular processes are large, and their facets are oriented in the coronal plane. The facets of the superior articular
processes face posteriorly and slightly superior, while the facets of the inferior articular processes face anteriorly and slightly inferior. The spinous processes of C2-C6 may or may not be bifid. The C7 spinous process is the longest and most prominent cervical spinous process.

The first two cervical vertebrae are adapted for movements of the head. The atlas, C1, is attached to and “holds up” the skull. The axis, C2, provides the axis upon which the atlas and the attached skull can rotate. The atlas lacks a body and is composed of an anterior and posterior arch connected on each side to lateral masses. The lateral masses contain superior and inferior articular facets. The superior facets face superiorly and articulate with the occipital condyles of the occipital bone, while the inferior facets face inferiorly and articulate with the superior facets on the body of the axis. The internal surface of the anterior arch contains a small facet for articulation with the dens of the axis. Projecting off of the anterior arch is an anterior tubercle, while projecting off of the posterior arch is the posterior tubercle, which replaces the spinous process. The transverse processes are prominent and contain the vertebral foramina. On the superior surface of the posterior arch is a groove for the vertebral artery as it crosses the arch to enter the vertebral canal. The axis consists of a body and a vertical dens projecting superiorly off of the body. The dens has anterior and posterior facets for articulation with the facet on the anterior arch of the atlas and the transverse ligament of the atlas. The axis has no superior articular processes but does have superior articular facets on each side of the body. Its inferior articular processes, spinous process, and transverse processes resemble those of other cervical vertebrae.

In the cervical spine two types of joints, other than the uncovertebral joints described previously, unite cervical vertebrae C2-C7. These include facet joints (zygapophyseal joints) and intervertebral body joints (intervertebral discs). The facet joints are synovial joints between the articular processes of adjacent vertebrae. A thin, loose articular capsule surrounds each joint. The facet joints permit gliding movements between the vertebrae, and the shape of the articular surfaces limits the range of motion possible. Branches arising from the posterior primary rami of the spinal nerves innervate these joints. The intervertebral discs are fibrocartilaginous joints, designed for weight bearing and strength, situated between the bodies of adjacent vertebrae. Each intervertebral disc consists of an outer anulus fibrosus, composed of concentric lamellae of fibrocartilage, which surrounds a gelatinous nucleus pulposus. The anuli insert into the rounded rims on the articular surfaces of adjacent vertebral bodies. Branches arising from the anterior primary rami of the spinal nerves innervate the intervertebral discs. The intervertebral discs are avascular structures, which receive their blood supply by diffusion from the vertebral bodies.

Ligaments reinforce and stabilize the facet joints and the intervertebral discs between the C2-C7 vertebrae. The anterior and posterior longitudinal ligaments resist anterior and posterior displacement of the vertebral bodies on one another. The anterior longitudinal ligament limits extension of the vertebral column. The posterior longitudinal ligament runs within the vertebral canal beginning at C2 and limits flexion of the vertebral column. The strong, highly elastic, flattened ligamenta flava attach to the laminae of adjacent vertebrae to preserve the normal curvature of the vertebral column and straighten the vertebral column after it has been flexed. Short interspinous ligaments join adjacent spinous processes. In the cervical spine, the supraspinous ligament is replaced by the ligamentum nuchae, which separates the muscles on each side of the posterior neck and provides attachment for them. On its deep service, it attaches to the spinous processes of the cervical vertebrae, while superiorly it attaches to the external occipital protuberance and median nuchal line. Its posterior margin spans the distance between the external occipital protuberance and the spinous process of C7. This ligament helps to support the weight of the head when it is flexed.

The atlanto-occipital facets are obliquely positioned and permit nodding of the head and some lateral bending with practically no rotation.
The three atlantoaxial joints are specialized for head rotation. The median atlantoaxial joint is a pivot, with the atlas pivoting around the dens and carrying the head with it. Several strong ligaments provide the stability of the atlanto-occipital and atlantoaxial joints, most importantly the transverse ligament of the atlas, which converts the anterior arch of the atlas into a complete ring around the dens. The dens is connected to the occipital condyles of the occipital bone by the alar ligaments, which limit flexion and rotation. Extending superiorly and inferiorly from the transverse ligament of the atlas are superior and inferior crura, which together form a ligamentous complex referred to as the cruciform ligament. All of these ligaments lie deep to an upward extension of the posterior longitudinal ligament called the tectorial membrane.

The vertebral artery, which traverses the transverse foramina of the cervical vertebrae, typically arises from the subclavian artery at the base of the neck medial to the anterior scalene muscle. It runs superiorly and slightly posterior and usually enters the transverse foramen of the sixth cervical vertebra. Along with the artery are postganglionic sympathetic nerve fibers derived from the cervicothoracic or stellate ganglion and the vertebral vein. In the neck, small branches of the vertebral artery supply adjacent deep muscles of the neck and spinal branches enter the intervertebral foramina to supply the spinal cord and its coverings.

Muscles help to stabilize the spine and control the effects of gravity (Fig. 16.1.4). In the cervical spine two major functional groups of muscles are present: extensors and flexors. Each group is also capable of rotating and lateral bending the cervical spine. The extensor muscles are situated posterior to the laminae and transverse processes of the cervical vertebrae. These muscles also lie deep to the cervical portion of the thoracolumbar fascia, which separates them from more superficial muscles (trapezius and rhomboids) attaching the spine to the upper limb.

The extensor muscles can be divided into four groups: the splenius, erector spinae, transversospinalis,
and suboccipital muscles. These muscles are arranged in three layers. The superficial layer contains the erector spinae and the splenius muscles. The intermediate layer contains the semispinalis and multifidus muscles of the transversospinalis group. The deep layer contains the interspinal, intertransverse, and rotator muscles of the transversospinalis group and the suboccipital muscles. The splenius muscles consist of the broad splenius capitis and the narrow splenius cervicis. The erector spinae muscles in the neck include the following from superficial to deep:

The multifidus muscles, lying deep to the semispinalis muscles, are thin in the cervical region. They arise from the articular processes of the lower four cervical vertebrae, run medially and superiorly and attach into the spinous processes of the axis and the upper two or three cervical vertebrae below the axis. The interspinous, intertransverse, and rotator muscles lie deep to the multifidus and are fairly well developed in the cervical region.

The suboccipital muscles connect the atlas and the axis to each other and to the skull and function in rotating and extending the head. This muscle group is composed of major and minor rectus muscles and superior and inferior oblique muscles. The rectus muscles produce extension of the atlanto-occipital joints, whereas the oblique muscles rotate the atlas and the skull on the axis. The major and minor oblique muscles and the major rectus muscle form the borders of the suboccipital triangle. This triangle contains the vertebral artery, suboccipital nerve, which supplies all of the suboccipital muscles and sensory greater occipital nerve.

The flexor muscles of the cervical spine are important in raising the head from a supine position. These prevertebral muscles in the cervical region are in close apposition to the vertebral column, directly flex the spine, and are represented by the longus colli and scalene muscles. The sternocleidomastoid muscle, attaching superiorly to the mastoid process of the skull and inferiorly to the manubrium of the sternum and the clavicle, is a more powerful flexor of the cervical spine than the prevertebral muscles because of its more anterior position. Not only does it draw the head forward but it also flexes the cervical spine. The sternocleidomastoid is also the most powerful rotator of the cervical spine but it works in combination with other muscles. The prevertebral muscles are innervated by the anterior primary rami of the cervical spinal nerves, while the sternocleidomastoid muscle is innervated by the accessory nerve (CN XI).

The spinal cord and its coverings (meninges) are located in the vertebral canal of the cervical spine. The cervical spine contains eight cervical spinal cord segments along with their anterior and posterior nerve roots. Cervical spinal nerves (eight pairs) are formed just outside the intervertebral foramina by the union of the anterior and posterior roots. In the cervical spine, the spinal nerves are formed above the vertebra they correspond to in number. Thus, the C1 spinal nerve is formed between the skull and the atlas, while the C8 spinal nerve is formed just outside the intervertebral foramen between the C7 and T1 vertebrae. After the spinal nerve is formed, it divides almost immediately into anterior and posterior primary rami. The posterior primary rami innervate segmentally skin and muscles of the back as well as the facet joints of the cervical spine. Communications between the anterior primary rami of the C1-C4 spinal nerves form the cervical plexus deep to the internal jugular vein and the sternocleidomastoid muscle in the neck. The phrenic nerve is the motor nerve to the diaphragm; it arises from the C3-C5 roots and descends through the neck on the anterior surface of the anterior scalene muscle down to the diaphragm.

The brachial plexus is derived from the anterior primary rami of the C5-T1 spinal nerves and provides motor and sensory innervation to the upper limb (Fig. 16.1.5). The
plexus extends from the neck into the axilla and is composed of roots, trunk divisions, cords, and branches. The roots and trunks with their branches lie in the posterior triangle of the neck, with the roots situated between the anterior and middle scalene muscles along with the subclavian artery. Branches in the neck include the dorsal scapular nerve (C5) to the rhomboid and levator scapulae muscles, the long thoracic nerve (C5-C7) to the serratus anterior muscle, and the suprascapular nerve (C5 and C6) running laterally across the posterior triangle of the neck to supply the supraspinatus and infraspinatus muscles and the shoulder joint.

There are several important soft tissue landmarks in the neck (Fig. 16.1.4.) The sternocleidomastoid muscle extends from the mastoid process of the skull to the manubrium of the sternum and clavicle, and divides the neck into anterior and posterior triangles. The muscle is palpable along its entire length. A lymph node chain is situated along the medial border of the sternocleidomastoid muscle. The trapezius muscle extends from the external occipital protuberance to the T12 vertebra and attaches laterally into the clavicle, the acromion, and the spine of the scapula. The muscle can be palpated along its superior border from its origin to its distal attachment. The trapezius and the sternocleidomastoid share a continuous attachment along the base of the skull to the mastoid process as well as a common nerve supply by way of the accessory nerve (CN XI). The superior border
of the trapezius forms the posterior boundary of the posterior triangle of the neck. The thyroid gland lies in the anterior triangle of the neck at the level of the C5-T1 vertebrae. It consists of right and left lobes located anterolateral to the larynx and trachea. An isthmus connects the lobes across the trachea on the midline of the neck at the level of the second to third tracheal rings. The esophagus, posterior to the trachea, begins at the inferior border of the thyroid cartilage and passes inferiorly through the superior thoracic aperture into the thorax. The carotid sheath is a fascial tube that extends from the base of the skull to the root of the neck deep to the sternocleidomastoid muscle in the anterior triangle of the neck. It contains the common and internal carotid arteries, internal jugular vein, and vagus nerve (CN X). At the level of the superior border of the thyroid cartilage, the common carotid artery divides into the internal and external carotid arteries. The root of the neck (supraclavicular fossa) is at the junction between the neck and the superior thoracic aperture. It is bounded anteriorly by the manubrium of the sternum, laterally by the first rib, and posteriorly by the body of the T1 vertebra. The sternocleidomastoid muscle, as it approaches its distal attachment, and covered by the platysma muscle, can be palpated.

The temporomandibular joint (TMJ) is a synovial joint, anterior to the auricle of the ear, where the head of the condyle of the mandible articulates with the articular tubercle and the mandibular fossa of the temporal bone (Fig. 16.1.6). An articular disc divides the joint cavity into superior and inferior compartments each lined by a synovial membrane. The fibrous capsule attaches superiorly to the margins of the articular area on the temporal bone and around the neck of the condyle. The capsule is thickened laterally to form the lateral ligament, which strengthens the TMJ. Two additional ligaments connect the mandible to the skull but add little strength to the TMJ. The stylomandibular ligament extends from the styloid process of the temporal bone to the posterior aspect of the angle of the mandible. The sphenomandibular ligament, medial to the TMJ, runs from the spine of the sphenoid bone to the lingula of the mandible.