PROCEDURE - ORAL CAVITY
1.
PRE-WORK
(before lab) review
the mandible and
oral cavity
region of the human skull from your atlas or a skull in the
lab.
(Netter011)
(Netter013)
(Netter015)
Mandible - The body of the mandible extends laterally and posteriorly to each side forming a horseshoe-like shape holding the inferior teeth. On the inside of the mentum (tip of the chin) are several attachment points for muscles
These are the genioglossus forming much of the tongue, and the roughly central geniohyoid, anterior belly of the digastric, as well as the wider mylohyoid extending along the inside or the mandible to each side. We'll examine these below
Palate - On the base of the skull between the rows of upper teeth is the horizontal process of the palatine bone and the palatine process of the maxilla.
These contributes to the anterior roof of the oral cavity and the floor of the nasal cavity.
Pharynx - The pharynx is a shared air and food space subdivided into the nasopharynx (region posterior to the nasal cavity), oropharynx (region posterior to the oral cavity, and laryngopharynx (region posterior to the larynx).
2. Fold back the blue drape and unzip/open the body back, but do not unclip the inner plastic covering the donor.
These donors are under dissection by the Dental program and the inner layers should remain covering the donors to prevent dehydration while we are working.
3. Remove the hemi-head from the translucent organ box under the table and use one of the trays to form a surface on top of the donors covered legs as your work area.
Note, the nasal passages have been disected by the MS2 students in their airways sessions. Thus, you will not see intact nasal passages and the region will be open to the maxillary sinus. The nasal passages are a region you will study in the respiratory section of the MS2 CRP course.
4. Observe the tongue, part of which forms the anterior wall of the oropharynx.
(Figure778)
(Netter077)
(Netter071)
The anterior 2/3rd of the tongue is the oral region (typically called the body), the posterior 1/3rd is the pharyngeal region (typically called the root).
The pharyngeal part of the tongue forms the anterior wall of the oropharynx.
The division between the anterior 2/3rd and posterior 1/3rd is marked by a lateromedial groove, the terminal sulcus.
In the midline of the dorsum of the tongue, separating the tongue into left and right, is the shallow groove of the median sulcus.
This is not visible in the hemi-head as the centerline cut passes through the median sulcus. It is visible if a lab member protrudes their tongue (or you use a mirror later) to observe the median sulcus in the living.
The tongue surface is covered by papillae. The anterior 2/3rd contains filiform and fungiform papillae, while the sulcus terminalis groove has a row of circumvallate papillae.
5. Identify at midline the cut surface of the mandible and the cut surface of the
hyoid bone.
(Photo7084)
(Netter077)
Since the hyoid bone is quite small, palpating for a hard bony point in a line posterior to the mandible should locate it.
While the airways are continuous from oral/nasal to the lungs, the level of the hyoid bone demarcates the boundary level for the oropharynx superiorly and laryngopharynx inferiorly.
6. Gently dissect the superficial fascia deep to the skin inferior to the
mandible and identify the cross-section of the thin mylohyoid muscle.
(Photo7084)
(Netter077)
The mylohyoid is the most superficial muscle spanning from the mandible to the hyoid bone at the midline and extends laterally forming the floor of the mouth.
The anterior belly of the digastric muscle is superficial to the mylohyoid muscle, but at a slightly more lateral position. Thus, at the midline the digastric muscle is not yet visible.
7. Dissect gently deep to the mylohyoid muscle for fibers of the geniohyoid
muscle which span from the mandible to the hyoid bone.
(Photo7084)
(Netter077)
The fibers of the geniohyoid muscle blend into the genioglossus muscle of the tongue along the superior aspect, however, they are defined by whether they insert onto the hyoid bone. If the fibers insert onto the hyoid bone they are part of the geniohyoid. Contraction pulls the hyoid bone anteriorly.
8. Observe the muscle fibers of the genioglossus muscle which originate at the
mandible and arch 'fan-like' to make up most of the body of the tongue.
(Photo7084)
(Netter077)
The genioglossus muscle has a single bony attachment to the inside of the mandible. The other ends of the muscle anchor into the connective tissue of the tongue. Fibers of the genioglossus muscle constitute the majority of the mass of the tongue.
The genioglossus muscle can flatten and protrude the tongue by pulling the body of the tongue anteriorly towards the mentum, which extrudes the tip of the tongue past the lips.
All the muscles that have a bony anchor and insert into the connective tissue framework of the tongue are the extrinsic muscles of the tongue. These have glossus, meaning 'of the tongue', in their name (genioglossus, hyoglossus, styloglossus and palatoglossus muscles).
The only extrinsic muscle of the tongue not innervated by the hypoglossal nerve (XII) is the palatoglossus muscle, which receives innervation from branches of the Vagus nerve (X).
9. Examine the dorsal and anterior (tip) of the tongue where muscle fibers are
with orientations are intermixed.
(Netter077) (Netter068)
(Photo7084)
These are fibers of the intrinsic muscles of the tongue which originate and insert within the connective tissue of the tongue (i.e. they have no bony attachments).
The muscles consist of interwoven small fascicles of muscle and are not easily identifiable as discrete muscles at the gross level.
The intrinsic muscles are the vertical, transverse, superior longitudinal, and inferior longitudinal fascicles (named by their direction).
The four intrinsic muscles of the tongue (vertical, transverse, superior longitudinal, and inferior longitudinal fascicles) and three of the four extrinsic muscles of the tongue (genioglossus, hyoglossus, and styloglossus muscles) are all innervated by the hypoglossal nerve (XII).
10. Examine the base of the tongue just posterior to the terminal sulcus for a
series of bumps or 'roughening' of the surface.
(Figure778)
(Figure729)
(Netter071)
(Netter077)
These bumps are the dispersed nodules of the lingual tonsils. The lingual tonsils typically have a less defined arrangement and smaller individual size than the palatine tonsils, often consisting of a singular midline patch of tissue.
11. Depress and retract the body of the tongue medially so
that you can examine the lateral wall for the palatoglossal and palatopharyngeal
arches.
(Figure729a)
(Netter065)
(Netter072) (Photo7135)
Palatoglossal arch - The palatoglossal arch is the more anterior arch formed by the mucosa 'bump' over the palatoglossal muscle. As the name implies, this spans from the posterior palate inferiorly into the tongue.
Palatopharyngeal arch - The palatopharyngeal arch is the more posterior arch formed by mucosa over the palatopharyngeal muscle. This runs from the palate inferiorly into the pharynx, acting to lift the pharynx during swallowing.
12. Examine the region between the palatoglossal and
palatopharyngeal arches for a lump like structure of the palatine tonsils.
(Figure729a)
(Netter065)
(Netter072) (Photo7135)
Note, in the age group of our donors when they were children it was standard of care in tonsillitis to frequently perform a tonsillectomy. Thus, it is likely that in many/most of our donors the bulk or entirety of their palatine tonsils have been removed and only some small mucosal folds (scar tissue) may be present.
If you have a distinct tonsil, show nearby tables so that they may review a palatine tonsil if their donor does not have one.
Due to the deep cleft arrangement of the palatine tonsil microstructure, the palatine tonsils more readily entrap food/bacteria compared to other tonsils. Thus, the palatine tonsil is the most likely to become infected causing tonsillitis.
13. Using a blunt probe, identify the extent of the hard
palate (bony) located in the anterior roof of the mouth and the soft palate
(muscular) located at the posterior roof of the mount.
(Netter065)
(Netter077) (Photo7084)
The centerline of the soft palate ends in a variably sized protrusion of mucosa covered muscle (musculus uvulae) collectively called the uvula. The function of the soft palate and uvula are to close off the nasal passages during swallowing.
The soft palate is tensed and elevated during swallowing by a pair of small muscles called the tensor veli palatini and the levator veli palatini respectively. These are within and lateral to the palate and not observable.
14. Examine the cut midline edge of the posterior
pharyngeal wall and observe the posterior wall is formed by a layer of muscle fibers.
(Figure732b)
(Netter077) (Netter078)
These are the constrictor muscles forming the outer layer of pharyngeal muscle. These muscles are designated superior, middle, and inferior constrictors based upon relative location. However, these are essentially a continuously muscular wall with no gaps between these muscles (other wise food would escape!).
Inferior to the larynx the constrictor muscles become contiguous with the muscle wall of the esophagus.
Although not apparent in a hemi-head, the left and right side constrictor muscles meet at the a midline raphe. Raphe is a general term for a union of similar tissues, usually muscle, that connect without the presence of an intermediate tendon or aponeurosis.
We will not examine the inner layer of pharyngeal muscles (palatopharyngeus, salpingopharyngeus, and stylopharyngeus). These inner vertically orientated pharyngeal muscles lift the pharynx to close of the larynx during swallowing, while the outer circular muscles of the constrictors primarily propel food inferiorly into the esophagus.
15. Follow the posterior wall of the phaynx superiorly to
the most posterosuperior recess where the nasophayrngeal tonsils are located.
(Figure729) (Netter077)
This posterosuperior recess houses the nasopharyngeal tonsils (also known as the adenoids) in the posterior wall of the pharynx. Unless inflammed, these tonsils are not visually distinct.
16. Work inferiorly to a mucosal bump and opening located
just posterosuperior to the soft palate.
(Figure729) (Netter077)
This bump is the torus tubarius formed by the cartilage of the eustachian tube. The tubal tonsils are located in the mucosal wall just posterior to the opening of the eustachian tube.
17. Return to the base of the tongue and examine infeirorly
on the anterior wall of the laryngopharynx for the
curved 'paddle' of the epiglottis.
(Netter065)
(Netter077) (Photo7084)
During swallowing the epiglottis is pressed over the opening of the larynx to prevent food or liquids from entering the trachea.
18. Push your finger over the top of the epiglottis down to
the lateral side where food is diverted into the piriform recess before
continuing into the esophagus.
(Netter079) (Photo7136)
The piriform recess is a common location for sharp items ingested to become lodged in the pathway (e.g. fish bones).
PROCEDURE - RETROPHAYRNGEAL
19. Starting slightly inferior to the level of the skull, push a blunt probe into the fascia between the posterior wall of the naso- and oropharynx and the anterior surface of the vertebral bodies.
(Figure732a)
(Netter072)
(Netter078)
(Photo7087)
This separates the posterior wall of the pharynx (containing from inside to outside, the mucosal surface, a band of constrictor muscles, and the buccopharyngeal fascia against the posterior side of the constrictor muscles) from the prevertebral fascia surrounding the musculoskeletal pedestal of the neck (vertebrae and neck muscles).
20. Work the probe inferiorly along the anterior surface of
the vertebral bodies separating the posterior wall of the pharynx all the way to
the inferior cut surface of the hemi-head.
(Figure732a)
(Netter072)
(Netter078)
(Photo7087)
These layers separates very easily forming a 'gap' between them which is the retropharyngeal space.
The retropharyngeal space is a potential space bounded anteriorly by the buccopharyngeal fascia (against the posterior side of the constrictor muscles) and posteriorly by the prevertebral fascia (against the vertebral bodies).
The retropharyngeal space is continuous from the base of the skull into the mediastinum. Thus, serious oral infections (e.g. a tooth abscess) that enters the retropharyngeal space can readily spread inferiorly into the mediastinum.
Some texts will describe an alar fascia layer as a separate layer just anterior to the prevertebral fascia. However, the nuances of fascial layers of this region of the neck are for specialists.
21. With the retropharyngeal space opened, dissect
away part of the fascia against the posterior wall of the pharynx to find branches of a nerve
plexus.
(Figure737)
(Netter089) (Netter082)
(Photo7088)
These are nerve fibers of the pharyngeal plexus that is formed by branches of the vagus, glossopharyngeal, and sympathetic chain.
Anterior to the pharyngeal nerve plexus lie the pharyngeal muscles innervated by branches from the plexus.
22. Search further into the retropharyngeal space to the
lateral side of the pharynx where there will be superior to inferior oriented
elements of the sympathetic chain.
(Figure736)
(Netter141)
(Photo7089)
The cervical sympathetic trunk lies against the anterior side of the prevertebral muscles and the posterior side of the pharynx close to the internal carotid artery. If you are careful you may observe nerve branches emerging from the sympathetic chain into the buccopharyngeal fascia to join the pharyngeal plexus.
The trunk consists of a superior, middle, and inferior cervical ganglia, however, only the superior cervical ganglion will be dissected in this lab (typically the middle and inferior ganglia are more inferior than the hemi-head cut through the neck).
Superior cervical ganglia: The superior cervical ganglion is the largest and lies on the level of C2. It is shaped like an elongated or flattened football and can be as large as 2-4cm in length.
Middle cervical ganglia: The middle ganglion at approximately C6 is small and in some cases absent.
Inferior cervical ganglia: The inferior ganglion at approximately C7, on or in close proximity to the neck of the first rib, is also small and is frequently fused with the ganglion of T1 (the fused ganglia is then called the cervicothoracic or stellate ganglion).
Branches arising from the superior cervical ganglia spread out following the external carotid artery branches onto the face (to blood vessels and sweat glands) and other branches follow the internal carotid artery into the skull (to deeper head structures such as blood vessels and the dilator pupillae of the eye)
The cervical sympathetic ganglia also give rise to the three cardiac branches of the sympathetic trunk (superior, middle, and inferior cardiac nerves) that descend into the thorax to distribute fibers to the cardiac plexus and heart.
PROCEDURE - SUPRAHYOID
23. Turn the hemi-head over so that you can work on the lateral side.
24. Remove skin and superficial fascia (including the platysma) from the lateral neck.
A useful guide to depth is to follow the anterior surface of the sternocleidomastoid and also to continue from the facial incision line along the mandible inferiorly removing skin over the lateral neck.
The platysma muscle is one of the muscles of facial expression and consists of a thin sheet of muscle fibers oriented superior to inferior 'draping' from the mandible down to the clavicle.
The muscle functions to tighten/wrinkle the skin of the neck during speech or head/neck movement and has a minor role in opening the jaw.
This muscle frequently becomes less distinct with age, contributing to the looser skin tone of elderly individuals. Thus, in our donors there may only be residual fibers present in the subcutaneous tissue.
25. The subdivision of the anterior triangle of the neck
associated with the floor of the mouth is the suprahyoid region.
(Figure746)
(Netter036)
The suprahyoid region is everything between the hyoid bone and the mandible.
In some texts you will see this region divided into the submental triangle (a midline triangle bounded by the anterior digastric muscles) and the submandibular triangle (a triangle located between the digastric muscles and the mandible). This has no clinical relevance.
26. Start at the midline inferior to the mandible and clean
fascia to expose the anterior end of the anterior belly of the digastric muscle.
(Figure750)
(Figure773) (Netter035)
(Netter036)
(Photo7022)
Trace the anterior belly of the digastric muscle inferiorly to where it becomes tendinous just superior to the hyoid bone.
This tendinous region hooks through a ligament attached to the hyoid bone and then becomes a muscle again continuing superolaterally.
This superolateral extension is the posterior belly of the digastric muscle. It attaches posteriorly to the mastoid process of the skull (follow it posteriorly only as far as approximately the angle of the mandible at this time).
Note, the posterior belly is straddled/crossed by another muscle, the stylohyoid muscle, which we will not be examining in detail.
Thus, the digastric muscle consists of two muscle bellies (anterior and posterior) connected by a tendinous region.
27. Superior to the hyoid bone at the midline and deep to
the anterior belly of the digastric muscle lies the mylohyoid muscle.
(Figure750)
(Figure773) (Netter035)
(Netter036)
(Photo7022)
The mylohyoid muscle is flat and triangular arising from the entire length of the mylohyoid line along the inside of the mandible coursing inferomedially to attach to the hyoid bone. This forms the floor of the mouth.
Keeping the anterior belly of the digastric muscle intact, clear fascia working medial to lateral so you can see the flat inferior surface of the mylohyoid muscle.
28. As you approach the posterior edge of the mylohyoid
muscle observe the C-shaped submandibular gland.
(Figure773)
(Netter039)
(Netter036)
(Photo7022)
The gland overlaps the posterior edge of the mylohyoid muscle such that part of the gland is inferior to the muscle edge and part of the gland superior.
The facial artery passes over, or through, part of the submandibular gland before passing over the edge of the mandible onto the superficial face.
In the vicinity of the submandibular gland are numerous lymph nodes receiving lymphatic's from the oral cavity. These nodes continue inferiorly posterior to the submandibular gland following the cervical lymph node chain coursing with the carotids on each side of the neck.
These lymph nodes may be palpable if they are inflamed. Unless your donor had an oral/pharyngeal infection at the time of their passing, these lymph nodes will not be apparent.
29. Using a blunt probe mobilize the inferior aspect of the
gland of the submandibular gland such that it can be retracted.
(Figure773)
(Netter039)
(Netter036)
(Photo7022)
The submandibular gland will vary in size between individuals. If the gland is large, in steps below parts of the submandibular gland inferior to the mylohyoid can be dissected away as needed.
30. Return to the tendinous hook of the digastric muscle
and observe the stylohyoid and posterior belly of the digastric muscle directed
posterosuperior from the hyoid bone.
(Figure773)
(Netter039)
(Netter036)
(Photo7022)
At this stage in dissection without seeing the skull originations it is not always easy to determine the stylohyoid muscle from the posterior belly of the digastric muscle as the trajectory of the muscles are near parallel.
The stylohyoid muscle attaches to the hyoid bone and extends posteriorly to attach to the styloid process of the skull while the posterior belly of the digastric attaches to the mastoid process.
Expose the muscles posteriorly to as far as approximately the angle of the mandible at this time.
31. Blunt dissect into the fascia in the space formed by
the posterior edge of the mylohyoid and the anterior edge of the posterior belly
of the digastric muscle to find the hypoglossal (XII) nerve.
(Netter039)
(Netter041)
(Photo7023)
The hypoglossal nerve courses anterior to the carotid arteries and deep to the posterior belly of the digastric muscle immediately superior to the tip of the greater cornu (horn) of the hyoid bone.
If the hypoglossal nerve is not apparent between the digastric and mylohyoid, look slightly posterior and deep to the posterior belly of the digastric muscle for where the hypoglossal nerve courses anteriorly past the carotid artery.
This may be easier after the step below where the tendon of the digastric is cut and reflected.
Due to the morbidity associated with hypoglossal nerve damage (the inability to control the tongue on the affected side), protecting this nerve is a high priority in any neck surgery.
32. Transect the tendon of the posterior belly of the digastric and stylohyoid muscles (be careful not to also cut the hypoglossal (XII) nerve) and reflect the muscles laterally.
PROCEDURE - CAROTID
33. The next subdivision of the neck is the carotid
triangle.
(Figure746)
(Netter036)
(Netter039)
The vascular compartment of the neck courses on each side of the neck deep to the sternocleidomastoid muscle and lateral to the trachea and esophagus.
The vessels are surrounded by the carotid sheath, a thin, tube-like, layer of fascia enclosing the common carotid artery, internal jugular vein and associated deep cervical lymph nodes. Inside the sheath between and posterior to the two vessels is the vagus nerve.
Immediately posterior and outside of the sheath is the sympathetic trunk you observed in the retropharyngeal dissection above.
34. Use scissors to open the carotid sheath at the cut surface of the hemi-head low in the neck, reflecting the sternocleidomastoid muscle as needed.
35. Open the sheath and observe the vagus nerve as it
courses within the carotid sheath.
(Figure752)
(Netter039)
(Netter041)
(Photo7025)
The vagus nerve lies between the carotid artery and internal jugular vein and slightly posterior to them. You may need to retract the vessels to see the vagus nerve.
The vagus gives off branches to the pharynx and larynx as it passes those structures. The vagus is the major neural control for vocal communication of the laynx as well as the function of the pharynx during swallowing.
36. Continue opening the sheath working superiorly to the
bifurcation of the internal and external carotid arteries.
(Figure753)
(Netter041)
(Netter147)
(Photo7025)
The common carotid artery bifurcates into the internal and external carotid arteries at approximately the level of the superior edge of the thyroid cartilage.
In some individuals the bifurcation can occur high in the neck making it difficult (or near impossible) to see all of the arterial branches of the external carotid in the steps below. If that is the case observe as much as you can (any tissue posterior to the carotid arteries may be removed to open your field of view).
37. Observe a slight swelling or dilation in the diameter
of the common carotid artery at the bifurcation.
(Figure753)
(Netter041)
(Netter147)
(Photo7025)
The dilation in the vessel here is the carotid sinus which is sensitive to pressure changes in arterial blood. The size of the swelling is quite variable and often indistinct.
In the crotch between the two vessels is a small mass of tissue within the vessel wall, the carotid body (not visible to the naked eye). The carotid body is primarily sensitive to oxygen content of the blood.
While the carotid body does contribute to respiratory drive, the strength of this drive is limited. The major driving force for respiration is via central chemoreceptors in the brainstem that are highly sensitive to carbon dioxide level in the blood.
38. Follow the external carotid artery superiorly to
where you may observe several anteriorly directed arteries arising from the
external carotid artery.
(Figure753)
(Netter041)
(Netter147)
(Photo7026)
(Photo7027)
(Photo7028)
These anteriorly directed vessels will be the lingual artery and the facial artery (in approximately 20% of people the lingual and facial arteries arise from a common trunk). We will not follow these to their final destinations as it is difficult to gain access at this location due to the mandible.
If you observe an artery turning inferiorly, that vessel is the superior thyroid artery. The lingual and facial arteries arises just superior to the superior thyroid artery.
Lingual Artery: The lingual artery passes deep to the mylohyoid sending branches entering the tongue and supplying the floor of the mouth.
Facial Artery: The facial artery arises anteriorly and courses over or through part of the submandibular gland in a tortuous path (coiled/weaving). The artery passes across the mandible where the constant pulsing of the artery over the lifetime causes a small notch to form on the mandible (about 1/3 of the distance from the ear to the chin). At that location, it is possible to feel the facial pulse in the living.
Post-Lab Daily Clinical Review Cases
Each lab has several multiple choice practice cases to reinforce understanding of the material within the lab and associated lectures. These are optional to review at home for consolidating and testing understanding.
CHECKLIST
Skeletal Structures
Mandible
Hard Palate
Hyoid Soft Structures
Soft Structures
Spaces
Nasopharynx
Oropharynx
Laryngopharynx
Piriform recess
Retropharyngeal
space
Mylohyoid muscle
Geniohyoid muscle
Genioglossus muscle
Intrinsic muscles of the tongue (as a group)
Lingual tonsils
Palatine tonsils
Palatoglossal arch
Palatopharyngeal arch
Soft palate
Uvula
Constrictor muscles
Epiglottis
Sympathetic chain
Superior cervical
ganglia
Submandibular gland
Hypoglossal nerve
Vagus nerve
Anterior belly of the digastric muscle
Posterior belly of the digastric muscle
Common carotid artery
Internal
carotid artery
Carotid sinus
External carotid artery