Dissector Answers - Nasal Cavity and Pharynx

Learning Objectives:

Upon completion of this session, the student will be able to:

1. Describe the nasal cavity, its general morphology including walls, openings, nasal septum, conchae, meatuses, and its general neurovascular supply.
2. List the paranasal sinuses and where each opens into the nasal cavity.
3. Describe the hard and soft palate.
4. Describe the pharynx and its subdivisions, its muscular and fascial components, its general neurovascular supply, and its anatomical relationships.
5. Describe the location and neurovascular supply of the pharyngeal, palatine, and lingual tonsils.
6. Describe the location of the deep cervical lymph nodes and the general pattern of their afferent and efferent channels.

Learning Objectives and Explanations:

1. Describe the nasal cavity, its general morphology including walls, openings, nasal septum, conchae, meatuses, and its general neurovascular supply. (N37A, N37B, N37C, N42A, N42B, N43, N44, N45, N46, N47, TG7-41, TG7-42, TG7-43A, TG7-43B, TG7-45AB, TG7-45CD)

Walls of the nasal cavity:

• Roof - primarily the cribriform plate of the ethmoid bone.
• Floor - hard palate formed by palatine processes of the maxillae and the horizontal processes of the palatine bones
• Medial wall - nasal septum
• Lateral wall - inferior, middle, and superior concha project from the lateral wall. Beneath each is a space or meatus - inferior meatus, middle meatus, and superior meatus. Above and behind the superior concha is a sphenoethmoidal recess.

Openings: nostrils or nares open onto the face, and choanae open posteriorly into the nasopharynx.

Nasal septum: anteriorly, the septum is cartilagenous; posteriorly, it is bony. The upper bony septum is formed by the perpendicular plate of the ethmoid, which articulates below with the vomer.

Meatuses:

• inferior meatus - receives the nasolacrimal duct (conducting tears from the orbit) anteriorly
• middle meatus - the bulla ethmoidalis projects medially beneath the middle concha, with middle ethmoidal air cells opening on its surface. Below the bulla, a curved groove, the hiatus semilunaris, receives the frontonasal duct from the frontal sinus anterosuperiorly. Posteroinferiorly, it receives the maxillary sinus. Between these openings the anterior ethmoidal air cells empty into the hiatus.
• superior meatus - receives the posterior ethmoid air cells
• sphenoethmoidal recess - receives the sphenoid sinus

Nerve supply: Olfactory epithelium, containing olfactory nerves, is found in and near the roof. Anteriorly, branches of the anterior ethmoidal nerve from ophthalmic division of trigeminal nerve (CN V₁) distribute. Lateral wall - posterior superior and inferior lateral nasal branches. Nasal septum - nasopalatine nerve.

Blood vessels: Sphenopalatine artery supplies most of the nasal cavity via its posterior lateral nasal branches and its septal branches. Branches of the anterior and posterior ethmoidal arteries also reach the anterior and superior portions of the nasal cavity.

2. List the paranasal sinuses and where each opens into the nasal cavity. (N41A, N41B, N41C, N52, N53, TG7-43A, TG7-43B, TG7-44A, TG7-44BC)

Frontal sinus: middle meatus via hiatus semilunaris
Maxillary sinus: middle meatus via hiatus semilunaris
Ethmoid air cells (small air spaces within the ethmoid bone):

• anterior ethmoid air cells - middle meatus via hiatus semilunaris
• middle ethmoid air cells - middle meatus via bulla ethmoidalis
• posterior ethmoid air cells - superior meatus

Sphenoid sinus: sphenoethmoidal recess

3. Describe the hard and soft palate. (N63, N64A, N64B, TG7-23, TG7-24)

The hard palate is formed primarily by the palatine processes of the maxillary bones, with the horizontal processes of the palatine bones forming the posterior third. The soft palate stretches posteriorly. It is a fibromuscular septum that can be moved to close off the nasopharynx.

4. Describe the pharynx and its subdivisions, the action of its musculature during swallowing, and its general neurovascular supply. (WB 235; N 35, 63, 65, 66, 67, N125, 126, 130, TG 7-10A, 7-10B, 7-20, 7-21, 7-22, 7-24)

The pharynx is the multi-purpose chamber that connects the nasal and oral cavities superiorly with the esophagus and larynx inferiorly. It is multi-purpose in that it is the common pipe for food, liquids, and air, and it is the job of the pharynx to see that these invaluable items travel through the right pipe to the proper destination.

The pharynx is the part of the digestive system posterior to the nasal and oral cavities, extending posteriorly and inferiorly past the larynx. It extends to the inferior border of the cricoid anteriorly and the inferior border of C6 posteriorly, where it continues below as the esophagus. The posterior wall of the pharynx lies against the prevertebral layer of deep cervical fascia. The retropharyngeal space is an important potential space behind the pharynx. Infections that gain access to this retropharyngeal space may potentially track down through the neck and into the chest.

In the pharynx the paths of food and air cross. Food travels from the mouth (anterior) to the esophagus (posterior). Air travels from the choanae (posterior) to the trachea (anterior).

The interior of the pharynx is divided into 3 parts:

• nasopharynx, most superior, is behind the nasal cavity and superior to the soft palate. It is strictly respiratory. Air enters the nasopharynx through the posterior openings of the choanae, which are bisected by the posterior edge of the nasal septum. At the upper posterior end of the nasopharynx is the pharyngeal tonsil, which is lymphoid tissue known as adenoids when enlarged. The auditory tube to the middle ear opens into the lateral wall of the nasopharynx. Its opening is covered by the torus tubarius. The salpingopharyngeal fold is a vertical fold of mucous membrane extending inferiorly from the opening of the auditory tube.
• oropharynx, the middle portion of the pharynx, is posterior to the oral cavity and connects with the nasopharynx above and the laryngopharynx below. The dorsum of the tongue is anterior to the oropharynx. The inferior border of the oropharynx is the epiglottis. Anteriorly it is continuous with the oral cavity at the palatopharyngeal folds or arches.
• laryngopharynx, the most inferior part of the pharynx, lies below the oropharynx and posterior to the larynx. It extends from the epiglottis superiorly down to the inferior border of the cricoid at C6. Its posterior and lateral walls are formed by the middle and inferior pharyngeal constrictor muscles. Internally, the walls are formed by palatopharyngeus and stylopharyngeus muscles. The laryngeal inlet connects the laryngopharynx with the larynx. (Aside: Lateral to the laryngeal inlet are the piriform recesses, where foreign bodies can become lodged.) The laryngopharynx is continuous inferiorly with the esophagus.

Structure of the pharynx:

The wall of the pharynx is composed of 6 muscles and associated fascia. Three ring-like constrictor muscles - the superior, middle, and inferior pharyngeal constrictors - contract serially to push the bolus of food down to the esophagus. Three longitudinal muscles - palatopharyngeus, stylopharyngeus, and salpingopharyngeus - elevate the larynx and widen the pharynx to accommodate the bolus during swallowing. The fascia covering the outside of the posterior of the pharynx is the buccopharyngeal fascia, part of the deep cervical fascia called visceral fascia, because it envelopes the viscera of the neck - the pharynx, larynx, and thyroid and parathyroid glands. The pharyngobasilar fascia is a submucosal layer which lies beneath the mucous membrane of the pharynx and adds support in areas where the layer of constrictor muscles is deficient. Behind the pharynx is, logically enough, the retropharyngeal space, lying between the buccopharyngeal fascia and the fascia enveloping the vertebral column and its associated musculature, called the prevertebral fascia. Laterally, the retropharyngeal space is continuous with parapharyngeal spaces on either side. Infections can track into these spaces, and then travel down into the chest as far as the diaphragm. Acute tonsillitis, infections involving the palatine tonsils, are especially capable of spreading infections into the parapharyngeal spaces. Such peritonsillar abscesses are referred to as quinsy.

Innervation of the pharynx:

Motor:
Pharynx muscles are innervated by branches from pharyngeal plexus with 2 exceptions: stylopharyngeus (glossopharyngeal, CN IX) and tensor veli palatini (supplied by mandibular division of trigeminal, V₃). Other than these two exceptions, the vagus is the source of motor innervation to the pharynx. The inferior pharyngeal constrictor also receives innervation from the recurrent laryngeal and external branch of the superior laryngeal (which are also derived from the vagus).

Sensory:
The sensation of the three parts of the pharynx are carried by three different cranial nerves, with considerable overlap of sensory fields. Sensation from the nasopharynx is primarily carried by the maxillary division of the trigeminal nerve V₂, while the oropharynx served by the glossopharyngeal nerve, Cranial Nerve IX. Sensation from the laryngopharynx is primarily through branches of the vagus nerve, CN X.

5. Describe the location and neurovascular supply of the pharyngeal, palatine, and lingual tonsils. (N 35, 63, 65, 66, 67, 125, 126, 130, 7-22, 7-23, 7-30, 7-39)

The pharyngeal tonsil is located on the roof and posterior wall of the nasopharynx. It is often referred to as adenoids when enlarged. It is located immediately above and behind the torus tubarius, the elevation that marks the nasopharyngeal opening of the auditory tube. Enlargement of the pharyngeal tonsil may obstruct the nasal choanae, reducing air flow from the nasal cavity into the nasopharynx. Adenoids may also compress the auditory tube and hinder its function, leading to middle ear infection (otitis media). Some lymphoid tissue, termed a tubal tonsil, may extend inferolaterally behind the opening of the auditory tube.

The palatine tonsil is located below the soft palate and above the tongue, between the palatoglossal and palatopharyngeal folds (a space referred to as the bed of the palatine tonsil or the tonsillar fossa). They are bilateral, and are often referred to as THE tonsils.

The lingual tonsil is located on the root of the tongue, posterior to the sulcus terminalis.

Tonsilectomy is not performed as frequently as it once was, but under certain circumstances, the removal of all three types of tonsillar tissue (tonsil and adenoid removal, sometimes called a "T and A") is necessary.

Arteries supplying the tonsils: The pharyngeal tonsil is supplied by branches of the maxillary artery, such as artery of the pterygoid canal and its pharyngeal branch, as well as the ascending pharyngeal artery from external carotid. The palatine tonsil is primarily supplied by the tonsilar branch of the facial artery, along with its ascending palatine branch, branches of the dorsal lingual artery from lingual, lesser palatine branches from descending palatine artery, and the ascending pharyngeal. The lingual tonsil is supplied by branches of the dorsal lingual artery.

Nerves supplying the tonsils: The pharyngeal tonsil receives sensory innervation from branches of the maxillary division of the trigeminal nerve, which supplies most of the nasopharynx. The palatine and lingual tonsils receive sensory innervation from the glossopharyngeal nerve, which passes forward through the inferior part of the tonsilar fossa to reach the posterior third of the tongue. Glossopharyngeal nerve may be damaged here during tonsillectomy.

6. Describe the location of the deep cervical lymph nodes and the general pattern of their afferent and efferent channels. (N72, TG7-74)

The deep cervical nodes are mostly lateral and posterior to the IJV. The nodes are divided into superior and inferior subgroups at the point where the omohyoid muscle crosses over the IJV. Thus, those deep nodes above this crossing are the superior deep cervical lymph nodes and those below the crossing are the inferior deep cervical lymph nodes. Channels from the inferior deep cervical lymph nodes, also called supraclavicular nodes, join to form the jugular lymphatic trunks, which usually join the thoracic duct on the left side and the right lymphatic duct on the right side (sometimes it will enter the right venous angle directly).

The jugulodigastric node is a relatively large deep cervical node located just below the posterior belly of the digastric. It receives lymph from the naso- and oropharynx and other head structures. It often swells in response to infection in the palatine tonsils.

The juguloomohyoid node is a deep cervical node located near the crossing of the carotid sheath by the omohyoid muscle. It receives lymph mainly from the lips, anterior oral vestibule and cavity, and tongue tip. Cancers in this region, sometimes seen in tobacco users, may track to this node.

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Questions and Answers:

7. Consider the structure and functions of conchae. (N37A, N37B, N37C, N70, TG7-22, TG7-43A, TG7-43B)

The concha are scroll-like in shape. Also called turbinates, they cause inspired air to be turbulent so as to facilitate the warming and humidifying action of the mucous membrane, whose surface area is increased by the conchae.

8. Consider drainage of sinuses and air cells. (N37A, N37B, N37C, N52, N53, TG7-43B, TG7-44A, TG7-44BC)

See above.

9. Where is the lingual tonsil? (N58, N63, TG7-39)

The lingual tonsil is in the submucosa on the superior surface of the root of the tongue just behind the sulcus terminalis. It is a collection of lymphoid nodules that give the posterior one-third of the tongue its warty appearance.