8: Systemic Anatomy of the Head and Neck

Chapter 8 imageSystemic Anatomy 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).

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.

DRAINAGE OF SPECIFIC STRUCTURES AND AREAS

4 Cranial Nerves and Cranial Autonomics

CRANIAL NERVES

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.

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.

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.

Jan 5, 2015 | Posted by in General Dentistry | Comments Off on 8: Systemic Anatomy of the Head and Neck
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