Chapter 8 Systemic Anatomy of the Head and Neck

4. Cranial Nerves and Cranial Autonomics 368

1 Arteries

The arteries that ultimately supply the head and neck originate from the subclavian and common carotid arteries. On the right side, the common carotid and subclavian arteries originate from the brachiocephalic artery just posterior to the right sternoclavicular joint in the root of the neck. On the left side, the common carotid and subclavian arteries originate separately from the arch of the aorta within the superior mediastinum.

The arteries of the head and neck are illustrated in Figure 8-1 and listed in Table 8-1. Regional detailed descriptions of the arteries are found in Chapter 7.

Figure 8-1 Arteries of the head and Neck. A, Right external carotid artery and its branches. B, Right internal carotid and vertebral arteries and their branches within the skull.

TABLE 8-1 Arteries of the Head and Neck

2 Veins

The venous drainage of the head and neck may be conveniently grouped into a set of external or superficial veins and a set of deep or intracranial veins. The superficial veins drain to either the external jugular vein or the internal jugular vein; the deep veins drain to the internal jugular vein.

The external jugular vein picks up tributaries from posterior superficial structures of the head and face and descends along the sternocleidomastoid muscle. Inferiorly, it enters the posterior triangle and joins the subclavian vein.

The internal jugular vein drains intracranial structures, leaves the skull through the jugular foramen, and descends in the neck within the carotid sheath. At the root of the neck, it joins the subclavian vein to form the large brachiocephalic vein. In the superior mediastinum the right and left brachiocephalic veins unite to form the superior vena cava, which, in turn, drains to the right atrium of the heart.

The veins of the head and neck are illustrated in Figures 8-2 and 8-3 and listed in Table 8-2. Regional detailed descriptions of the veins are found in Chapter 7.

Figure 8-2 Superficial veins of the head and neck.

Figure 8-3 Deep veins of the head and neck and communications with facial vein.

TABLE 8-2 Veins of the Head and Neck

3 Lymphatics and Lymph Nodes

Knowledge of the routes by which lymph flows from the head and neck back to the venous system is essential to understand lymphatic spread of infections and cancer (Table 8-3). For a general discussion of the lymphatic system, see Chapter 1, Section 6.

TABLE 8-3 Lymph Nodes of the Head and Neck

Lymph Node	Structures Drained (Afferents)	Efferents
Superficial Horizontal Ring
Submental	Lower lip, chin, tip of tongue, anterior floor of mouth	Submandibular nodes, jugulo-omohyoid nodes
Submandibular	Submental nodes, cheek, nose, upper lip, maxillary teeth, vestibular gingivae, mucosa and gingivae of the hard palate, posterior floor of mouth, lateral aspects of anterior two thirds of tongue	Nodes of deep cervical chain
Parotid (Preauricular)
Superficial	Eyelids, temples, prominence of the cheek, auricle	Deep parotid nodes, deep cervical nodes
Deep	Middle ear, external auditory meatus, soft palate, posterior aspect of nasal cavity, superficial parotid nodes	Deep cervical nodes
Mastoid (retroauricular)	Scalp, auricle	Deep cervical nodes
Occipital	Posterior scalp	Deep cervical nodes
Deep Horizontal Ring
Retropharyngeal	Posterior nasal cavity, nasopharynx, soft palate, middle ear, external auditory meatus	Deep cervical nodes
Paratracheal, pretracheal, prelaryngeal, and infrahyoid	Larynx, trachea, pharynx, esophagus	Deep cervical nodes
Deep Cervical Vertical Chain
Jugulodigastric, jugulo-omohyoid, and other nodes of the cervical chain	Entire chain receives afferents from the superficial horizontal ring of nodes and the deep horizontal ring of nodes	Left side: joins thoracic duct at junction of left subclavian and internal jugular veinsRight side: joins right subclavian and right bronchomediastinal lymph trunks to enter junction of right subclavian and right internal jugular veins

The lymphatics of the head and neck, as in other areas of the body, drain toward groups of lymph nodes. The nodes act as filters and add lymphocytes to the lymph fluid. In the head and neck, the lymph nodes may be conveniently grouped into (1) a horizontal ring of superficial nodes, (2) a horizontal ring of deep nodes, and (3) two vertical chains of deep cervical nodes. Both horizontal rings drain to the two deep vertical chains (Figure 8-4).

Figure 8-4 A, Scheme of lymphatic drainage of head and neck. B, Coronal section through the upper neck to show scheme of lymphatic drainage to deep cervical trunk.

SUPERFICIAL RING OF NODES

The superficial ring surrounds the transition area of neck to head and is arranged into five main groups (Figure 8-5; see Table 8-3). These nodes are palpable when infected.

Figure 8-5 Lymphatic drainage of the face. SMe, Submental nodes; SMd, submandibular nodes; P, parotid (preauricular) nodes; M, mastoid (postauricular) nodes; O, occipital nodes.

DEEP RING OF LYMPH NODES

A deeper horizontal group of lymph nodes surrounds and drains the visceral structures of the neck. The deep ring, in turn, drains outwardly to the vertical chain of deep cervical nodes.

Retropharyngeal Nodes

The retropharyngeal nodes lie within the retropharyngeal space, that is, the fascial space between the posterior wall of the pharynx and the prevertebral fascia of the vertebral unit.

Afferent Vessels

The retropharyngeal nodes receive afferents from (1) the posterior nasal cavity and nasopharynx, (2) the soft palate, and (3) the middle ear and external auditory meatus.

Efferent Vessels

The efferent vessels drain to the upper group of deep cervical nodes.

Paratracheal, Pretracheal, Prelaryngeal, and Infrahyoid Nodes

The paratracheal, pretracheal, prelaryngeal, and infrahyoid nodes lie lateral and anterior to the visceral structures of the neck.

Afferent Vessels

The paratracheal, pretracheal, prelaryngeal, and infrahyoid nodes receive afferents from (1) the larynx and trachea and (2) the pharynx and esophagus.

Efferent Vessels

The efferent vessels drain to the deep cervical nodes.

DEEP CERVICAL (JUGULAR) VERTICAL CHAIN

The deep cervical chains descend from the base of the skull down to the root of the neck, and they parallel the courses of the right and left internal jugular veins. The deep cervical chain receives afferent drainage from the nodes of the superficial ring and the deeper visceral ring of lymph nodes. As the deep cervical chains approach their terminations, they form the right and left jugular lymph trunks.

On the left side, the jugular trunk joins the thoracic duct or enters the junction of the subclavian vein and internal jugular vein independently. On the right side, the right jugular, subclavian, and bronchomediastinal lymph trunks may join to form a common right lymphatic duct, which, in turn, empties to the confluence of the right subclavian and internal jugular veins. Alternatively, the right jugular trunk may independently enter the venous system at the same point.

Two large nodes are singled out in the deep cervical chain: (1) the jugulodigastric and (2) jugulo-omohyoid nodes.

DRAINAGE OF SPECIFIC STRUCTURES AND AREAS

Teeth

The maxillary teeth drain to vessels that pass to the face via the infraorbital canal and then pass inferiorly to enter the submandibular nodes.

The mandibular dental lymphatics drain backward through the mandibular canal and end in the deep cervical nodes.

Gingivae

The vestibular gingivae of the mandibular and maxillary arches drain to the submandibular nodes.

Mandibular lingual gingivae and the mucosa of the floor of the mouth drain to the submandibular nodes or directly to the deep cervical chain. The anterior segment drains initially to the submental nodes.

The maxillary palatal gingivae and the palatal mucosa drain to the submandibular or to the retropharyngeal nodes.

Lips

The upper lip drains to the submandibular nodes; the lower lip drains to the submental nodes.

Tongue

The tip of the tongue drains to the submental lymph nodes, the lateral aspects of the anterior two thirds drain to the submandibular nodes, and the medial portion of the anterior two thirds drain directly to the deep cervical nodes (Figure 8-6).

Figure 8-6 Drainage of lymph from various areas of the tongue and palatine tonsils.

The posterior third of the tongue drains posteriorly to the retropharyngeal group of lymph nodes.

There is some crossing over the midline of lymphatic drainage of the tongue. Thus a lesion on one side of the tongue may spread to the opposite side via crossing lymphatics.

Palatine Tonsils

The palatine tonsils drain to the jugulodigastric node of the deep cervical chain.

Nasal Cavity, Paranasal Air Sinuses, and Nasopharynx

The anterior portion of the nasal cavity drains to the submandibular nodes. The posterior nasal cavity, sinuses, and nasopharynx drain directly to the deep cervical chain or indirectly via the deep parotid nodes or the retropharyngeal nodes.

Ear

Drainage of the auricle and external auditory meatus may be to the retroauricular or deep parotid nodes or directly to the deep cervical chain. The middle ear drains to the deep cervical chain.

Larynx and Trachea

The lymphatics of the larynx above the vocal cords drain initially to the infrahyoid nodes or directly to the deep cervical chain. The laryngeal lymphatic vessels below the vocal cords drain to the prelaryngeal and pretracheal nodes or directly to the deep cervical chain.

Lymphatic vessels of the trachea pass to the pretracheal and paratracheal nodes or pass directly to the deep cervical chain.

Pharynx and Esophagus

The lymphatic vessels of the pharynx and esophagus drain to the retropharyngeal or paratracheal nodes or may pass directly to the deep cervical nodes.

4 Cranial Nerves and Cranial Autonomics

A general description of the nervous system is found in Chapter 1, Section 7, and a description of the brain and attached cranial nerves is presented in Chapter 7, Section 2. In addition, a description of each cranial nerve is given as it appears in the various regions of the head. A summary of the cranial nerves is presented in Table 8-4.

TABLE 8-4 Cranial Nerves

Twelve pairs of cranial nerves arise from the brain. The first two nerves are remote from the brain and communicate with the brain via long extensions, or tracts. The remaining ten nerves arise directly from the brainstem.

Cranial nerves may perform one or more functions; possible functional components include (1) somatic afferent (general sensory from body structures), (2) visceral afferent (visceroceptive from glands and viscera), (3) special afferent (special sensory smell, sight, taste, hearing, and balance), (4) somatic efferent (motor to muscles derived from somites), (5) branchial efferent (motor to muscles derived from branchial arches), and (6) visceral efferent (autonomic motor to smooth muscle and glands).

Cranial Nerve I: Olfactory Nerve

Functional Component

The special sensation of smell is the only functional component of the olfactory nerve (Figure 8-7). The olfactory nerve originates from bipolar olfactory cells within the nasal mucosa, where peripheral processes end as specialized smell receptors in the mucosa covering the superior concha and upper nasal septum. Central processes collect as 18 to 20 branches of the olfactory nerve proper. These pass upward through the cribriform plate to the anterior cranial fossa and enter the overlying olfactory bulbs. Here they synapse with mitral cells, and their central processes pass back along the olfactory tract to the olfactory area of the forebrain.

Figure 8-7 Olfactory nerve (cranial nerve I).

Cranial Nerve Test

Each nostril, in turn, is challenged with various common odors. The patient is blindfolded and asked to correctly identify the odor. Lesions of the olfactory system result in loss of smell (anosmia).

Cranial Nerve II: Optic Nerve

Functional Component. The special sensation of sight is the sole functional component of this cranial nerve (Figure 8-8). Classically (but incorrectly) the optic nerve is described as the section that passes posteriorly from the eyeball to the optic chiasma. Actually, the optic nerve proper is contained within the retina of the eye and originates from rod cells (nondiscriminating sight) and cone cells (discriminating sight and color). These receptor cells occupy the most external portion of the retina and receive incoming light. Central processes pass inward to synapse with bipolar cells, which, in turn, synapse with ganglionic cells of the innermost layer. Central processes of the ganglionic cells collect and leave the eyeball as the optic nerve. The nerve, or tract, leaves the orbit through the optic canal, and right and left nerves join at the optic chiasma. Here the fibers originating from the medial (nasal) half of the retina decussate; the fibers of the lateral (temporal) half of the retina do not decussate. The optic tract continues posteriorly from the chiasma, and this ends in the lateral geniculate body of the thalamus, where the optic fibers synapse. Postsynaptic fibers pass posteriorly through optic radiations to the visual cortex in the occipital lobe of the cerebral hemispheres.