The oral vestibule is a narrow space between the labii & cheeks and the teeth. The oral vestibule communicates with the external environment via the oral fissure, and is continuous with the oral cavity proper posterior to the 3rd molars.

The oral vestibule contains the:

• • buccal surfaces of the teeth, alveolar processes, and associated gingivae,

  • papillae & openings of the parotid (Stensen’s) ducts,

  • openings of numerous minor salivary glands,

  • frenulum of upper lip, and

  • frenulum of lower lip.

The oral cavity proper is continuous with the oropharynx (via the oropharyngeal isthmus, the space between the palatoglossal arches). The oral cavity proper technically also contains the sublingual space, but this region is often conceptualized separately. 

The oral cavity proper (exclusive of the sublingual space) contains the:

• • lingual surfaces of teeth, alveolar processes, and associated gingivae,

  • tongue (body),

  • lingual frenulum

  • sublingual caruncles & openings of the submandibular (Wharton’s) ducts,

  • sublingual folds & openings of the sublingual ducts, and

  • openings of numerous minor salivary glands.

2. What are the contents and relationships of the sublingual space?

The sublingual (fascial) space is the area between the mucosa of the floor of the oral cavity proper and the mylohyoid m. Posterior to the margin of the mylohyoid m., the sublingual space is continuous with the submandibular fascial space (inferiorly) and lateral pharyngeal fascial space (posteriorly). Infections (mandibular odontogenic, or other) may spread from the sublingual space to adjacent spaces (submandibular, lateral pharyngeal, retropharyngeal, and beyond). Cellulitis (and related edema) in the sublingual, submandibular, and sometimes also the submental spaces may endanger the airway and require immediate intervention. This is known as Ludwig’s angina, and it is life-threatening.

The sublingual space contains:

• • sublingual glands (& associated ducts),

  • submandibular ducts,

  • lingual aa. (& brs.),

  • lingual vv. (& tributaries),

  • lingual nn. (& associated submandibular ganglia)

  • hypoglossal nn. (& vena comitantes)

  • deep lobe of submandibular gland.

 Of the three types of major salivary glands, the sublingual glands are the smallest. They are located superior to the mylohyoid m. and when covered with mucosa, form the sublingual folds. These glands drain via numerous small ducts along the sublingual folds. The deep, smaller part of the submandibular gland is also located in this area and is closely associated with the posterior end of the sublingual gland. 

The mylohyoid line of the mandible is formed by the attachment of the mylohyoid m. The two salivary glands in this region are associated with this line: sublingual gland superior, and submandibular gland inferior.

The lingual a. is typically the second branch of the external carotid a. that leaves the external carotid anteriorly. Passing between the hyoglossus m. and the middle pharyngeal constrictor m., the lingual a. supplies the floor of the oral cavity and the tongue. The lingual a. produces several branches, chiefly:

• • Dorsal lingual brs. - arise medially to the hyoglossus m.; supplies the posterior tongue, soft palate, and palatine tonsil,

  • Sublingual a. - arise anteriorly to the hyoglossus m.; supplies the sublingual gland, and muscles and tissues of the floor of the oral cavity, and

  • Deep lingual a. - the terminal br. of the lingual a. - lies along the inferior margin to the tip of the tongue; supplies the anterior tongue.

Nearly all of the lingual a. branches anastomose with their contralateral paired artery along the midline.

Deep to the mucosa in the oral cavity proper, the lingual n. and submandibular duct cross. The lingual n. descends into the oral cavity and loops under (‘cradles’) the submandibular duct to provide general sensory innervation to the anterior 2/3rds of the tongue.

The submandibular (Wharton’s) duct traverses the space between the submandibular gland and sublingual caruncle. The duct is located between the hypoglossal n. and lingual n. in association with the hyoglossus m. The lingual n. passes deep to the duct about midway in the oral cavity.

The lingual n. is an afferent branch of the posterior trunk of V3. It traverses the infratemporal fossa medial to the inferior alveolar n., where it is joined by the chorda tympani (branch of facial n., CN VII). Chorda tympani carries presynaptic parasympathetic fibers to the submandibular gland and taste to the body of the tongue (excluding the vallate papillae). The lingual n. enters the oral cavity superior to the mylohyoid m., and enters the tongue to provide sensory innervation to the body of the tongue and the floor of the oral cavity.

The submandibular ganglion is delicately associated with the lingual n. and is superior to the deep portion of the submandibular gland. This ganglion is one of four named peripheral parasympathetic ganglia (ciliary, pterygopalatine, submandibular, and otic). The submandibular ganglion receives preganglionic parasympathetic fibers from the chorda tympani, a branch of the facial n. (CN VII). Postganglionic parasympathetic fibers leave the ganglion to innervate the submandibular and sublingual glands, among other smaller glands (e.g. anterior lingual) by means of the lingual n., a branch of V3.

The vena comitans of hypoglossal n. is a tributary of the lingual v. This vein accompanies the hypoglossal n. (CN XII) inferiorly along the hyoglossus m.

3. Describe the innervation of the following: cheeks, teeth, and gingivae.

Cheeks (skin, buccinator m., and mucosa) are afferently innervated by the (long) buccal nn. (V3).

Teeth are innervated by alveolar nn. Maxillary teeth are innervated by superior alveolar nn. The superior dental plexus is composed of contributions from the superior alveolar brs. Posterior superior alveolar (PSA) brs. come directly from the maxillary n. (V2) in the pterygopalatine fossa. These branches descend deep to the mucosa of the maxillary sinus and afferently serve the maxillary molars. The middle superior alveolar brs. come from the infra-orbital n., and afferently innervate portions of the maxillary sinus and maxillary premolar teeth. The middle superior alveolar (MSA) brs. are frequently absent. Anterior superior alveolar (ASA) brs. also come from the infra-orbital n., and afferently serve the maxillary incisors and canines. Mandibular teeth are innervated by the inferior alveolar n. (IAN) and its brs.

Gingivae (gums) of the maxillary dental arch are innervated by brs. of V2, whereas gingivae of the mandibular dental arch are innervated by brs. of V3. See tables below for a summary.

4. Name the intrinsic and extrinsic muscles of the tongue and their origins, insertions and innervation.

Intrinsic tongue muscles: There are four types of intrinsic muscles of the tongue:

• • superior longitudinal,

  • inferior longitudinal,

  • transverse, and

  • vertical.

Intrinsic tongue muscles independently (and in unison) alter tongue shape and perform smaller, more precise movements. Intrinsic tongue mm. are innervated by the hypoglossal n. (CN XII).

Extrinsic tongue muscles: Extrinsic tongue muscles attach elements of the tongue to the skull and hyoid bone to affect gross movements of the tongue. Extrinsic tongue muscles are innervated by the hypoglossal n. (CN XII).

5. Describe the regions of the tongue, and the nerves and modalities serving these regions.

The tongue has dorsal (superior) and ventral (inferior) surfaces.

Dorsal surface:

The dorsal (superior) surface of the tongue is divided by paired terminal sulci into the body (presulcal/oral part) and root (postsulcal/pharyngeal part). A median sulcus runs superficial to a fibrous septum which runs the full length of the tongue, but the median sulcus ends in convergence with the terminal sulci. Where the three sulci converge is an indentation called the foramen caecum, an embryonic remnant of the thyroid diverticulum and thyroglossal duct. An outline of the three sulci resembles an arrow, pointing towards the root of the tongue and beyond. Just anterior to the inverted ‘V’ of the terminal sulci are two rows of vallate papillae, each running parallel to its adjacent terminal sulcus. The lateral end of each terminal sulcus extends to the palatoglossal arch. Thus, the body of the tongue rests roughly in the oral cavity proper, whereas the root of the tongue rests in the oropharynx. The root of the tongue extends from the terminal sulci (and associated palatoglossal arches) posteriorly to the epiglottic valleculae, where it is attached to the epiglottis via three folds: a median glosso-epiglottic fold (which separates the valleculae) and paired lateral glosso-epiglottic folds. The root of the tongue is devoid of papillae, but has a rugosa appearance due to submucosal collections of lymphatic nodules, collectively known as the lingual tonsil.

Ventral surface:

The ventral surface of the tongue is connected to the mucosa of the floor of the oral cavity via the lingual frenulum. It may be highly variable in size and attachment. In some individuals a shortened and thickened lingual frenulum may limit the mobility of the tongue, a condition known as ankyloglossia (‘tongue-tie’). Ablation of the lingual frenulum (frenulotomy) is less frequently performed to aid in difficulties with speech, but it may increase success of latching for breast feeding.

Sublingual folds laterally flank the lingual frenulum, and are formed by the sublingual glands and ducts of the submandibular glands shaping the mucosa. Along these folds are the bilateral openings of the sublingual ducts.

The sublingual caruncle is situated at the confluence of the sublingual folds and the lingual frenulum. The sublingual caruncle is the location where the submandibular (Wharton’s) ducts secrete saliva into the oral cavity proper.

Fimbriated folds flank the lingual frenulum on the ventral surface of the tongue. Typically, the lingual veins are visible deep to the inferior surface mucosa between the lingual frenulum and the fimbriated folds.

Innervation:

With the exception of the palatoglossal m. (vagus n.), the tongue is efferently innervated entirely by the hypoglossal n. (CN XII).

Afferently, the tongue has both general somatic and special visceral (taste) afferent innervations. An important landmark for the afferent innervation of the tongue are the vallate papilla (not the terminal sulci). In terms of somatic afferents:

• • areas anterior to the vallate papillae are innervated by the lingual n. (V3), whereas

  • areas posterior to the vallate papillae are innervated by the glossopharyngeal n.

There is a slight overlap of somatic afferent innervation in the posteromedial root of the tongue, which is innervated by both the glossopharyngeal n. and vagus n (via the internal br. of the superior laryngeal n.).  The vallate papillae also demarcate the two sources of special visceral afferent (taste) serving the taste buds:

• • anterior to the vallate papillae, taste is modulated via the facial n. (chorda tympani ← lingual n.), whereas

  • posterior to the vallate papillae, taste is modulated via the glossopharyngeal n.

6. Describe the various papillae of the tongue.

The lingual papillae consist of four types (from anterior to posterior):

• • Filiform papillae are small, conical eruptions covering the dorsal anterior two-thirds of the tongue. Filiform papillae are not associated with taste buds, but rather are important for the tactile sensation and manipulation of food items.

  • Fungiform papillae are moderately sized, mushroom-shaped eruptions interspersed throughout the filiform papillae. Fungiform papillae host taste buds innervated by the axons from chorda tympani (facial n.) by way of the lingual n. (V3).

  • Foliate papillae are found in trenches on the lateral margins of the tongue. Taste buds associated with foliate papillae are in greatest density during childhood, and often diminish with age.

  • Vallate papillae (sometimes referred to as circumvallate papillae) are located on the posteriormost border of the oral part of the dorsal tongue, just anterior to the terminal sulci and foramen caecum. These papillae are the largest of the lingual papillae. Vallate papillae host taste buds innervated by the axons from the glossopharyngeal n. (CN IX), even though they lie on the presulcal side of the tongue.

7. Describe the boundaries, muscles, fascia, vasculature, and innervation of the pharynx, and the boundaries of the retropharyngeal space.

BOUNDARIES:

The pharynx is a common space for the conductive pathways of the respiratory (gases) and digestive (food and drink) systems. As such, the pharynx shares borders with the nasal cavity (choanae), oral cavity (faucial isthmus), larynx (laryngeal inlet), and esophagus (entrance to esophagus).

The pharynx is divided into three regions, which reflect the above borders. They are the:

• • Nasopharynx (choanae; soft palate),

  • Oropharynx (soft palate; faucial isthmus; superior margin of epiglottis & pharyngo-epiglottic folds),

  • Laryngopharynx (superior margin of epiglottis & pharyngo-epiglottic folds; inferior margin of cricoid cartilage).

 MUSCLES:

The muscular wall of the pharynx consists of two layers: an outer layer of predominantly circular-oriented constrictors, and an inner layer of longitudinally oriented muscles that shorten and widen the pharynx. 

The three pharyngeal constrictor muscles in the external layer of the pharynx surround the pharynx, and meet along a posterior midline pharyngeal raphe. When activated, the pharyngeal constrictor mm. serially constrict the lumen of the pharynx.

The superior pharyngeal constrictor m. consists of four parts, each arising from a distinct location (associated by name), and coalescing posteriorly to the superior portion of the pharyngeal raphe. The four distinct parts (and their anterior attachments) include the:

• • pterygopharyngeal part (pterygoid hamulus & occasionally the posterior aspect of the medial pterygoid plate),

  • buccopharyngeal part (pterygomandibular raphe),

  • mylopharyngeal part (posterior portion of mylohyoid line of the mandible), and the

  • glossopharyngeal part (posterolateral tongue). 

The middle pharyngeal constrictor m. originates on the hyoid bone (greater and lesser horns) and the stylohyoid ligament, and inserts on the pharyngeal raphe.

The inferior pharyngeal constrictor m. consists of two parts. These parts (and their attachments) include the:

• • thyropharyngeal part (thyroid cartilage of the larynx), and the

  • cricopharyngeal part (cricoid cartilage of the larynx).

The three longitudinal muscles of the inner layer have a less coordinated anatomical arrangement than the constrictor muscles.

Stylopharyngeus m.

Palatopharyngeus m.

Salpingopharyngeus m.

NEUROVASCULATURE:

The pharyngeal constrictor mm. are innervated by the pharyngeal (neural) plexus, which receives efferent (motor) fibers from the vagus nn. (CN X) and afferent (sensory) fibers from the glossopharyngeal nn. (CN IX). The cricopharyngeal part of the inferior pharyngeal constrictor m. receives dual innervation from the pharyngeal (neural) plexus and the vagus n. (CN X) via the recurrent laryngeal n. and the superior laryngeal n. When activated, the pharyngeal constrictors serially constrict the lumen of the pharynx. Some fibers of the middle pharyngeal constrictor mm. can also act as an elevator of the pharynx. The plexus also receives autonomic fibers from the vagus n. (parasympathetic) and superior cervical ganglion (sympathetic).

The pharyngeal constrictor mm. are primarily supplied by the ascending pharyngeal a., a branch of the external carotid artery. Branches from the inferior thyroid a. also may supply the inferior pharyngeal constrictor m. Both superior and middle pharyngeal constrictor mm. may be partially supplied by tonsillar br. of the facial artery (also a branch of the external carotid a.). The superior pharyngeal constrictor m. may also receive blood from the ascending palatine a. (a br. of the facial a.).

The pharyngeal constrictor muscles are drained of blood by the pharyngeal venous plexus, which drains into the internal jugular vv.

FASCIA:

The pharynx is supported by two associated bodies of fascia: pharyngobasilar fascia and buccopharyngeal fascia. The pharyngobasilar fascia (the deep investing/epimysial layer of the external pharyngeal mm.) suspends the superior pharyngeal constrictor m. from the basilar part of the occipital bone and the adjacent temporal bone. The pharyngobasilar fascia is closely associated with the pharyngeal raphe at the pharyngeal tubercle. The buccopharyngeal fascia (the superficial investing/epimysial layer of the external pharyngeal mm.) consists of a thickened epimysium of the superior pharyngeal constrictor that extends anteriorly from the pharyngeal raphe to the superficial surface of the buccinator m. (of the cheek). A condensed band of the buccopharyngeal fascia that extends from the pterygoid hamulus to the posterior end of the mylohyoid line of the mandible is the pterygomandibular raphe. The pterygomandibular raphe connects the buccinator m. to the superior pharyngeal constrictor m.

RETROPHARYNGEAL SPACE:

The retropharyngeal space is a potential space posterior to the muscular wall of the pharynx (and its investing buccopharyngeal fascia), anterior to the prevertebral fascia, and spanning the distance between the base of the skull and the mediastinum (within the thoracic cavity). The retropharyngeal space is actually comprised of two potential spaces, separated by the alar fascia:

• • anterior, the “true” retropharyngeal space, and

  • posteriorly, the “danger space.”

The retropharyngeal space communicates laterally with the parapharyngeal spaces. Clinically, the retropharyngeal space is important, because it represents a potential pathway for metastasis of disease between the head & neck and the thorax.

8. Describe the neurovascular (arteries and nerves) that serve the larynx.

The larynx is exclusively innervated by the vagus n., specifically by means of the:

• Superior laryngeal n.:

  • External br.

    • Efferent to cricothyroid m. (intrinsic laryngeal muscle)

  • Internal br.

    • Afferent from laryngeal mucosa proximal to vocal folds

• Recurrent laryngeal n.:

  • Efferent to all intrinsic laryngeal mm. (except cricothyroid m.)

  • Afferent from laryngeal mucosa distal to vocal folds

Blood supply to the larynx comes from two major sources:

• Superior laryngeal a. (External carotid a. → Superior thyroid a. → Superior laryngeal a.)

  • Accompanied by the internal br. of the superior laryngeal n. through the thyrohyoid membrane.

• Inferior laryngeal a. (1st part of SCA → Thyrocervical trunk → Inferior thyroid a. → Inferior laryngeal a.)

9. Describe the laryngeal cartilages, membranes, muscles. Describe how the intrinsic muscles of the larynx affect either the positions of the vocal ligaments, or vocal pitch.

CARTILAGES:

The cartilaginous laryngeal skeleton is comprised of nine major cartilages. Three cartilages makeup the bulk of the laryngeal skeleton. They are the:

Thyroid cartilage:

• Most prominent cartilage

• Formed from two laminae, united anteriorly along the midline (posteriorly, the cartilage is incomplete)

• Suspended from the hyoid bone by the thyrohyoid membrane

• Superior horns loosely articulate with the greater horns of hyoid

• Inferior horns form the cricothyroid joint with the cricoid cartilage

• Cricothyroid joint allows for thyroid cartilage to ‘tip’ forwards

Cricoid cartilage:

• Forms a complete ring around the airway

  • Most robust posteriorly

Epiglottic cartilage: 

• Leaf-shaped cartilage

• Sits posterior to thyroid cartilage

• Forms the epiglottis

  • Forms a lid to cover the laryngeal inlet during deglutition (swallowing)

Three pairs of cartilages also help to support the structure and function of the larynx. They are the:

Arytenoid cartilages:

• Pyramid-shaped

• Sit atop the cricoid laminae (posterior)

• Vocal process (attaches to vocal ligament)

• Muscular process (allows for muscle attachment)

• Capable of either rotation or gliding

  • For either abduction, or adduction of vocal cords

Corniculate cartilages:

• Sit atop the arytenoid cartilages

• Extend the structure provided by the arytenoids posteromedially

  • Posterior portion of the laryngeal inlet

Cuneiform cartilages:

• Within the ary-epiglottic fold 

• Lateral portions of laryngeal inlet

MEMBRANES:

Two sheets of fibro-elastic connective tissue help to give shape to the walls of the larynx and laryngeal features: the quadrangular membrane and the conus elasticus. 

The quadrangular membrane is a poorly defined fibro-elastic sheet spanning the space between the lateral margins of the epiglottis and the arytenoid cartilages. The inferior-most extent of the quadrangular membrane forms the vestibular ligaments. 

The conus elasticus is a fibro-elastic sheet that shapes the walls of the larynx as a funnel between the thyroid and cricoid cartilages. The superior-most aspects of the conus elasticus are the vocal ligaments and the walls of the laryngeal ventricle. The anteromedial aspect of the conus elasticus is the (median) cricothyroid ligament, the connective tissue pierced during a cricothyrotomy.

INTRINSIC MM.:

Muscles that connect adjacent cartilages of the larynx are known as the intrinsic mm. of the larynx. These muscles either directly or indirectly affect the vocal ligaments, and therefore affect phonation (speech).

10. How is the sympathetic nervous system structured? What are the four basic pathways of pre-ganglionic sympathetic neurons? What are the major sources of sympathetics to the head & neck?

The sympathetic division of the autonomic nervous system consists of pre- and postganglionic fibers which typically (but not always) synapse in ganglia of the sympathetic trunk. Preganglionic fibers travel from the intermediolateral (IML) nucleus (lateral horn) of the spinal cord, out via the ventral roots of spinal nerves to the ventral primary rami (VPR), and then leave the spinal nerves via white rami communicantes (at levels T1-L2) to the sympathetic trunk. Once in the trunk, preganglionic fibers may:

• synapse at that level of the sympathetic trunk,

• leave the trunk as part of a splanchnic nerve (without synapsing), 

• ascend the sympathetic trunk (and then either synapse, or leave the trunk), or

• descend the sympathetic trunk (and then either synapse, or leave the trunk).

From the synapse, postganglionic fibers carry signals back to the VPR of the spinal nerve via gray rami communicantes. These fibers can then be distributed by the VPR. While white rami communicantes are restricted to the T1-L2 levels, the sympathetic trunks extend the entire length of the spinal cord, and gray rami communicantes conduct postganglionic fibers back to VPRs at every level of the cord. In the neck, there are typically 2-3 sympathetic ganglia, whereas in the thorax there are typically sympathetic ganglia at every spinal level (T1-T12).

Splanchnic nerves (collections pre-ganglionic fibers that pass through the sympathetic trunk without synapsing), typically synapse in the pre-aortic ganglia of the abdominopelvic cavity.