Head and Neck Lab 3B

Palatal structures:

In the previous lab members of your other group identified the palatal arches and their underlying muscles.  Now we’ll identify a pair of muscles that produce movements of the soft palate.  

As part of the swallowing reflex, the soft palate stiffens and moves superiorly to block off the nasopharynx.  If this didn’t happen, food or drink could find its way into the nasal cavity.  

The muscles that stiffen and elevate the soft palate are located in the lateral wall of the nasopharynx.  Strip off the mucosa of the nasopharynx inferior and just anterior to the torus tubarius to find these two muscles.  

The levator veli palatini m. is the muscle that elevates the soft palate.  Superiorly it attaches to the cartilagenous medial end of the pharyngotympanic tube, and inferiorly into the soft palate, so that when it contracts it pulls the soft palate superiorly.  

More lateral and slightly anterior to the levator veli palatini is the tensor veli palatini m.  The tensor has an odd course.  It attaches to the medial pterygoid plate of the sphenoid bone and runs inferiorly, but then turns 90 degrees as it runs around the pterygoid hamulus, so that it enters the soft palate from the lateral aspect of the soft palate.  When the tensor mm. on both sides contract they have the effect of pulling the soft palate taught from its edges, which stiffens it as the levator muscle pulls it superiorly.

The tongue:

Most of the space of the oral cavity is filled with the muscular tongue.  The tongue is composed of two sets of muscles.  The intrinsic muscles of the tongue are those muscles that are attached, at both ends to the tongue itself.  That is, the intrinisic muscles of the tongue do not attach to bone.  The function of the intrinsic muscles of the tongue is to change the shape of the tongue.  The intrinsic muscles of the tongue are named according to the direction of their muscle fascicles: longituindal muscles (run anterior to posterior), transverse muscles (run left to right), and vertical muscles (run superior to inferior).  Through coordinated contractions of these three sets of muscles that tongue can change its shape and contour.

The extrinsic muscles of the tongue attach to bone of the skull, jaw, or hyoid, and when they contract they move the tongue around within the oral cavity.  “glossus” is the latin root for “tongue”.  The extrinsic tongue muscles are typically named for their attachments, so glossus is typically part of their name.  There are 4 extrinsic tongue muscles.

The largest of the extrinsic muscles is the genioglossus m.  From a midline view the genioglossus m. fans out into the tongue from the deep surface of the chin.  The genioglossus may have multiple actions on the tongue (protrusion or depression), depending on what part(s) of the muscle are activated.

Now change to a lateral dissection of the tongue to find the remaining extrinsic tongue muscles.  Pull the tongue medially, and incise the mucous membrane between the tongue and the mandible.  Start at the lingual frenulum and carry the cut back to (but not beyond) the mandibular molar teeth.  Now use forceps to carefully remove the mucous membrane from the depression between the teeth and the base of the tongue.  

As you work in that space you’ll see salivary glands, arteries and nerves, but focus first on identifying the three remaining extrinsic tongue muscles.

Lateral to the genioglossus are the left and right hyoglossus m.  Each hyoglossus m. attaches from the hyoid bone to the tongue, and pulls the tongue posteriorly and inferiorly.

The superior lateral margin of the hyoglossus intermingles with another of the extrinsic tongue muscles that attaches superiorly to the styloid process, the styloglossus m.  The styloglossus pulls the tongue superiorly and posteriorly, and so is important in the initial phase of swallowing.  

The last of the 4 extrinsic tongue muscles is the palatoglossus m., which you revealed as part of dissection of the palatoglossal arch.  The palatoglossus m. also pulls the tongue superiorly and posteriorly.

Paranasal Sinuses:

Understand the paranasal sinuses (you may not be able to see them all in the skull bisection we have done, but will see more in the imaging module). These sinuses are air-filled extensions of the nasal cavity that are located in the:

• Frontal bone - the frontal sinus.  The frontal sinuses are paired, and sometimes connected across the midline

• Sphenoid bone - the sphenoid sinus.  There is a single midline sphenoid sinus that sits in the body of the sphenoid bone, just inferior to the sella turcica and medial to the cavernous sinuses (dural venous sinuses).

• Ethmoid bone - the ethmoidal air cells.  Sinuses are usually single larger spaces.  Air cells are sinuses that are divided into smaller spaces by connective tissue and epithelium.

• Maxillary bone - the maxillary sinus.  Paired sinuses just inferior to the orbits and lateral to the nasal cavity.  You’ll see these when you dissect the lateral wall of the nasal cavity.

The Nasal Septum

The nasal cavity is divided in the midline by the nasal septum. Identify the following in the half of the head that contains the nasal septum.

The choana (posterior nasal aperture) is the posterior opening between the nasal cavity and the nasopharynx.  Each half of the nasal cavity begins at the nostril and ends at the choana.  

The nasal septum is formed from 3 structures:

The perpendicular plate of the ethmoid bone superiorly.

The midline vomer bone below.  The vomer attaches inferiorly to the nasal crest of the maxillary and palatine bones.

The septal nasal cartilage anteriorly.  All of the nasal septum that sticks out from your face is composed of cartilage, with the bone forming the inner (posterior) part of the nasal septum.

Nerves and blood vessels that supply the nasal epithelium of the nasal septum travel between the nasal epithelium and the septum.  Carefully peel away the nasal epithelium from the nasal septum and look for the nerves and blood vessels.  You may only be able to see their impressions in the septum or the epithelium.

The posterior part of the septum is innervated by the nasopalatine n. (a branch of CN V2) and its blood supply is the sphenopalatine a. and v.  The anterior part of the septum is innervated by the anterior ethmoidal n. (a branch of CN V1), and its blood supply is the anterior ethmoidal a. and v.  

Now turn your attention to the lateral wall of the nasal cavity.  To increase the surface area of the nasal epithelium (which filters and humidifies inhaled air) there are 3 nasal conchae on the lateral wall.  Each concha has a core of thin bone, covered by nasal epithelium.  There is a space between each of the conchae and the lateral wall of the nasal cavity.  That space is called the meatus.

The inferior concha is a separate bone (not part of the ethmoid bone).  It’s posterior end is about 1 cm from the opening to the auditory tube.  The inferior meatus is the space between the inferior concha and the lateral nasal wall.

The middle concha is part of the ethmoid bone, and the middle meatus is the space between the middle concha and the lateral nasal wall.

The superior concha is also part of the ethmoid bone.  The superior concha is just anterior to the sphenoid sinus, and is covered by the olfactory epithelium (contain the olfactory receptors).  The superior meatus is the space between the superior concha and the lateral nasal wall.

Now use scissors to cut away the inferior nasal concha.  In the rostral (toward the nose) part of the inferior meatus look for the opening of the nasolacrimal duct (tear duct).  Tears drain from the medial canthus of the eye, through the nasolacrimal duct, and empty onto the nasal epithelium that lines the inferior meatus.  

Now cut away the middle nasal concha.  In the middle meatus you’ll see a curved slit, the hiatus semilunaris (or semilunar hiatus).  The maxillary sinus communicates with the nasal cavity through the hiatus semilunaris.  At the anterior margin of the hiatus, look for an additional opening that connects the frontal sinus to the nasal cavity.  

Posterior to the hiatus semilunaris is a raised structure, the ethmoidal bulla.  The ethmoid air cells are just lateral to the bulla, and the bulla has small holes in it that allow communication between the ethmoid air cells and the nasal cavity.  

Finally, look for an opening from the sphenoid sinus into the most superior part of the nasal cavity, the sphenoethmoidal recess.

Now peel away the remaining mucus membrane from the lateral nasal wall, posterior to the middle and inferior conchae.  Posterior to the conchae, but anterior to the torus tubarius, look for a raised region of translucent bone that runs vertically, toward the junction of the hard and soft palate.  That thin bone is the medial wall of the palatine canal, which contains the greater and lesser palatine nn., which arise from the pterygopalatine ganglion at the top of the canal.  

Use forceps or rongeurs to break through the thin bone covering the canal.  The contents of the canal (nerves and ganglia) are covered in a periosteal sheath.  Carefully cut the sheath to reveal the palatine nn.  Work your way superiorly along the canal to find the pterygopalatine ganglion (parasympathetic) at the top of the canal.  

The greater and lesser palatine nn. give branches off to the nasal mucosa that covers the lateral wall of the nasal cavity, and then pass through the greater palatine foramen and lesser palatine foramen.  The greater palatine n. supplies the mucus membrane of the roof of the mouth anterior to the palatine foraminae, and the lesser palatine n. supplies the mucus membrane of the roof of the mouth posterior to the palatine foraminae.  The nerves are accompanied by the greater palatine a. and v., and the lesser palatine a. and v.

Remove the remaining mucosa from the lateral wall of the nasal cavity, and break through that thin bone into the maxillary sinus.  Open the medial wall of the sinus broadly to allow a full view of the sinus.  Realize that the roof of the maxillary sinus is the floor of the orbit.  Within the thin bone of the roof of the maxillary sinus look for a channel (similar to the the palatine canal) that runs from posterior to anterior, the infraorbital canal.  The infraorbital n, a., and v. run in the infraorbital canal.  Open the floor of the canal with forceps, and trace the nerve back to the foramen rotundum.  The infraorbital n. , a., and v. divide to form anterior, middle, and posterior superior alveolar nn., aa., and vv., which supply sensory innervation and blood supply to the maxillary teeth.  Look at the floor of the maxillary sinus, you may see roots of the maxillary teeth.  The infraorbital n. continues through the infraorbital foramen to supply general sensory innervation to the skin of the face (dissected in a previous lab).