Primary Lab Objectives:
- Bisect the head.
- Examine the interior of the pharynx. Locate and dissect the pharyngeal tonsils. Identify and explore the opening of the auditory tube.
- Identify and uncover the palatoglossus and palatopharyngeus muscles forming the arches around the palatine tonsils.
- Examine the levator and tensor veli palatini muscles. Consider their roles in moving the soft palate.
- Locate the superior and middle constrictor muscles. Trace the stylopharyngeus muscle and follow cranial nerve IX running between the constrictors.
- Remove the palatoglossus, palatopharyngeus, and stylopharyngeus muscles, and examine the inner surface of the three pharyngeal constrictors.
Labs 24 and 25 proceed by examining specific regions of the bisected head in order. Some regions are covered today, including the pharynx, and the nerves and vessels of the hard palate. The next lab covers the tongue, muscles of the soft palate, and specific details of the nasopharynx, such as the conchae, sinuses, and associated nerves and vessels.
1. BISECTION OF THE HEAD
The next instructions entail careful bisection of the head and neck in the mid-sagittal plane, using a scalpel when possible and a hand saw when necessary. You should have already cut the posterior wall of the pharynx in the midline.
- Use a scalpel to divide the uvula and the soft palate in the median plane.
- Use a scalpel to cut through the upper lip just lateral to the midline.
- Use a scalpel to cut through the cartilages of the external nose just lateral to midline.
- Finally, use a scalpel to cut the tongue along the midline.
NOTE: The skull must be sawed just lateral to the median plane so you can see the nasal septum on one side and have a fully exposed surface on the other side.
- Saw through the skull from superior to inferior. Begin lateral to the crista galli and keep the blade close to the nasal septum.
- Cut through the frontal and nasal bones, ethmoid bone, body of the sphenoid (the dorsum sellae), basilar part of the occipital bone, and the hard palate. Stop when the saw has passed into the foramen magnum.
- Use a saw to cut through the mandible.
NOTE: you may have to gently chisel between central incisors in both the maxilla and the mandible to create a space for the saw to pass.
- Use a scalpel to cut through any remaining soft tissue as needed to complete the bisection.
2. INTERIOR OF PHARYNX
- Identify the hard palate, which separates the nasal cavities from the oral cavity.
- Identify the soft palate.
The soft palate functions as a swinging “valve”. It can swing up to block the nasopharynx or down to block the oral cavity. The muscles that control the soft palate are therefore critically important for controlling air and food/fluid flow in the pharynx.
- In the nasopharynx, locate the transected pharyngeal tonsil and the opening of the auditory tube.
- In the oropharynx, view the two arches formed by the palatoglossus and palatopharyngeus muscles (in the wall of the oral cavity behind the tongue).
3. PALATOPHARYGEAL AND PALATOGLOSSAL ARCHES
The palatine tonsils are collections of lymphoid tissue that play an immunological role. The palatine tonsils lie below the soft palate. They lie posterior to the palatoglossal arch that separate the oral cavity from the oropharynx and anterior to the palatopharyngeal arch. The palatine tonsils lie beneath the mucous membrane and encased in a hemicapsule of connective tissue that separates them from nearby muscles and nerves. These are sometimes called faucial tonsils because they lie between the oral cavity and oropharynx in a space called the fauces (similarly the palatoglossal and palatopharyngeal folds are often said to be faucial pillars).
- Using a NEW scalpel blade, carefully remove the mucosal lining of the pharynx, and expose the underlying musculature.
- Remove the palatine tonsil.
HINT: Removing a tonsil effectively from the surrounding capsule is a lengthy process and involves a delicate touch and patience.
- Identify the palatoglossus muscle going from the palate to the root of the tongue, and trace the palatopharyngeus muscle down into the pharynx.
HINT: These muscles are thin and may have been partially removed along with the mucosal lining. The best strategy is to look for their fibers running in the general direction indicated by thier names (i.e. from the palate to the tongue for the palatoglossus; from the palate to the pharynx for the palatopharyngeus).
The so-called palatoglossal arches or palatoglossal folds mark the boundary between the oral cavity and the oropharynx. Make sure you note this division. The palatoglossus runs from the soft palate to the tongue and has an action of raising the posterior tongue. Palatopharyngeus forms a fold or arch behind the palatoglossal fold/arch. The palatopharyngeus originates also from the soft palate, but it goes to the pharynx, where it enters the pharyngeal wall and runs deep to the superior constrictor and then eventually combines with the stylopharyngeus and serves to elevate the pharynx.
4. MUSCLES OF THE SOFT PALATE
- Dissect the muscles that operate on the soft palate and upper pharynx:
To see these muscles, remove the mucosa around the opening of the auditory tube.
- levator veli palatini, which elevates the soft palate
- tensor veli palatini, which tightens the soft palate (like the skin of a drum).
- salpingopharyngeus, which helps to elevate the pharynx during swallowing.
NOTE: These are very small muscles lying just under the mucosa. Make a small incision in the mucosa using your scissors or scalpel. Notice the muscle fibers just deep to the mucosa. Try to follow your incision making sure to cut only through the mucosa and avoiding the muscles as well as you can.
- Display the origins of the levator and tensor veli palatini muscles.
NOTE: This takes time and patience but is well worth it.
The levator veli palatini muscle travels inferiorly into the soft palate. When it contracts, it elevates the palate. The tensor veli palatini muscle follows a similar path, but goes more laterally, passing around the hamulus of the medial pterygoid plate. Thus, it changes its direction of pull to a transverse direction. This muscle tenses the soft palate, making it more rigid so that the levator veli palatini muscle can raise it up. The salpingopharyngeus muscle does not insert directly into the soft palate, but it helps to elevate the palate by pulling on the pharynx below. When raised, the soft palate blocks off the nasal pharynx so that food or liquid passing from the oral cavity to the oral pharynx does not go up into the nasal cavity.
Similar to the salpingopharyngeus muscle, part of the tensor veli palatini muscle attaches to the cartilaginous portion of the pharyngotympanic tube (aka 'auditory tube' or 'Eustachian tube'). When these muscle contract, they pull on the tube, widening the opening, and allowing the pressure between the oropharynx and the middle ear to equalize.
5. STYLOPHARYNGEUS MUSCLE
- Find the stylopharyngeus muscle along with its nerve (CN IX) entering between the superior and the middle constrictor muscles.
HINT: The separation of the constrictors looks great in images drawn by artists, but in reality, the divisions are often vague. You can help yourself to be sure of where each constrictor is by (a) looking for its origin and following fibers back to the raphe and (b) look for muscles and nerves that get into the pharynx between the constrictors.
The stylopharyngeus is a relatively large pharyngeal muscle coming down from the styloid process and slipping between superior and middle constrictors. It joins the palatopharyngeus and runs with it deep to the inferior constrictor down to the pharyngeal wall and thyroid cartilage.
A third muscle of the pharynx—salpingopharyngeus— also joins the palatopharyngeus and stylopharyngeus muscles. It arises near the auditory tube and you will see it in the next lab.
6. PHARYNGEAL CONSTRICTORS
- On one side only, carefully dissect away the longitudinal pharyngeal musculature (palatopharyngeus and stylopharyngeus muscles).
- Remove the palatoglossus muscle, in order to display the inner surface of the pharyngeal constrictors.
- Carefully examine the attachments of the three constrictors in front (anteriorly).
- Investigate their attachments above and below.
The lateral and posterior walls of the pharynx are composed primarily of the three pharyngeal constrictor muscles: superior, middle, and inferior.
- The superior constrictor arises from the posterior edge of the medial wall and hamulus of the pterygoid plate, as well as the pterygomandibular raphe (which is a narrow connective tissue band that runs from the pterygoid hamulus to the mandible, posterior to the 3rd molar), and the mandible.
- The middle constrictor arises from the superior surface of the greater horn of the hyoid as well as the stylohyoid ligament.
- The inferior constrictor arises from the oblique line on the thyroid cartilage and the arch of the cricoid.
The three constrictors fan posteromedially to form a wide insertion at a midline posterior raphe that runs from occiput to the esophagus. This insertion is complex with overlapping fibers that fuse with those above at the midline leaving interesting gaps between constrictors:
- The most superior fibers of the superior constrictor attach to the occiput at the pharyngeal tubercle.
- The uppermost fibers of the middle constrictor fan out, overlap, and fuse with the superior constrictor at the raphe.
- There is a gap between the superior and middle contrictors through which passes: (1) the styloglossus muscle, (2) the glossopharyngeal nerve, (3) the stylopharyngeus muscle.
- The uppermost fibers of the inferior constrictor overlap and fuse with the middle constrictor. The lowermost fibers of the inferior constrictor run down and blend with the esophagus. They are said to constitute a cricopharyngeus muscle.
The motor innervation of the pharyngeal constrictors is carried by the vagus nerve (CN X) and sensory innervation is carried by the glossopharyngeal nerve (CN IX).
Removal of tonsils is performed by dissecting the palatine tonsils from the tonsillar sinuses (fauces). Because of the rich blood supply of the tonsil, bleeding commonly arises from the large external palatine vein or from the tonsillar artery. The glossopharyngeal nerve accompanies the tonsillar artery on the lateral wall of the pharynx and is vulnerable to injury because the wall is thin. The internal carotid artery is especially vulnerable when it is tortuous as it lies directly lateral to the tonsil.
Inflammation of the pharyngeal tonsils (adenoids) is called adenoiditis. This condition can obstruct the passage of air from the nasal cavities through the choanae into the nasopharynx, making mouth breathing necessary. Infection from the enlarged pharyngeal tonsils may also spread to the tubal tonsils, causing swelling and closure of the pharyngotympanic tubes. Impairment of hearing may result from nasal obstruction and blockage of the pharyngotympanic tubes. Infection spreading from the nasopharynx to the middle ear causes otitis media (middle ear infection), which may produce temporary or permanent hearing loss.