Lab 4A
Oral cavity, Infratemporal fossa

This dissection is of the oral cavity and the deep structures of the jaw in the infratemporal fossa. This is a great opportunity to connect the nerves and vessels in the oral cavity with their origins in the infratemporal fossa.

Palatal structures:

We’ve seen the hard and soft palates, and followed the palatal nn., aa. and vv.  During the pharynx lab you 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.

At this point it will be helpful to review a couple of the suprahyoid muscles that you identified during dissection of the neck, the mylohyoid m. and the anterior belly of the digastric m.  Deep to the mylohyoid m. and now visible in the section of the tongue is another muscle of the floor of the oral cavity, the geniohyoid m.  The geniohyoid runs from the inner margin of the chin to the hyoid bone, and elevates the hyoid and thus the tongue during the initial stage of swallowing.  

Two salivary glands are visible.  The submandibular salivary gland curls around the inferior border of the mandible.  You saw the more superficial part of the gland during dissection of the face, and now you can trace it around the mandible to the deeper part of the gland that sits between the mandible and the tongue.  As you sort through nerves and vessels you may also find the submandibular salivary duct.  It looks similar to the parotid salivary duct, only smaller.  Also look for the more superior and anterior sublingual salivary gland.

The main artery you’ll find in this area is the lingual a.  The lingual a. is a branch of the external carotid a., and you should have found the more superficial part of it during an earlier lab.  The lingual a. gives off multiple branches to the muscles of the tongue, with the two main branches being the deep lingual a. and the sublingual a.  

Finally, there are two big nerves to identify.  You’ve already seen the hyopoglossal n. (CN XII) during your dissection of the neck and face.  Find it again externally, and then follow it into the tongue.  The hypoglossal n. is the motor n. to the tongue.  

Running superior to the hypoglossal n. is the lingual n., a branch of CN V3.  The fibers from V3 supply general sensation from the anterior 2/3 of the tongue.  Running along with the fibers from V3 is the chorda tympani n., a branch of the facial n. that carries taste fibers from the anterior 2/3 of the tongue.  Look for the submandibular ganglion hanging from the lingual n.  Preganglionic parasympathetic neurons in the chorda tympani n. (a branch of CN VII) enter the submandibular ganglion and synapse there with postganglionic parasympathetic neurons, which provide secretomotor (visceral motor) input to the sublingual and submandibular salivary glands.

On the surface of the tongue look for the large vallate papillae that form a V-shape.  Just posterior to the vallate papillae is the terminal sulcus, which separates the anterior 2/3 of the tongue from the posterior 1/3 of the tongue.  The posterior 1/3 of the tongue is covered by the lingual tonsils.

To begin, remove the bulk of the parotid gland to reveal the full extent of the masseter m.  Take care to preserve branches of the facial n. as you trim away the parotid gland.  

Reflect the masseter m. from the zygomatic arch and reflect it inferiorly.  Again, preserve branches of the facial n.

Now remove as much of the zygomatic arch as you can.  This will give you access to the mandible.  

You’ll make 3 cuts through the mandible.

1. Through the coronoid process.  The temporalis muscle attaches to the coronoid process.  Once you cut through the coronoid process you’ll be able to reflect the temporalis muscle superiorly.

2. Through the neck of the mandibular condyle.

3. Through the ramus of the mandible.  Take care when making this cut, as the inferior alveolar n. runs along inside of the ramus of the mandible before entering the bone through the mandibular foramen.  After you make the first two cuts, and before you make the third cut, try to work a blunt probe or a pair of forceps into the space between the inside of the mandible and the infratemporal fossa, and scrape the periosteum away from the bone.  This will help ensure you don’t cut the inferior alveolar n. when you cut through the mandible.  Also make your cut fairly superior.  After you remove the piece of mandible try to find the inferior alveolar n. and safeguard it as you make a more inferior cut in the ramus of the mandible to open the infratemporal fossa more broadly.  

Once you’ve removed the bone, use forceps to clean and clarify the dissection field of the infratemporal fossa.  Identify the two remaining muscles of mastication, the medial pterygoid m. and the lateral pterygoid m.  The lateral pterygoid is the more lateral of the two, and its muscle fascicles run from anterior to posterior (recall that it protracts the jaw, or pushes it forward).  You’ll see the medial pteryogoid m. emerging from beneath the inferior border of the lateral pterygoid, and its fascicles run superior to inferior (it’s mainly a jaw elevator).

Once you’ve identified the lateral pterygoid m. you need to remove it from the infratemporal fossa to view deeper structures.  While you are removing the muscle take care to preserve arteries and nerves that run through the fossa. The safest way to do this is to remove the muscle piece-meal, which means ripping or cutting out chunks of the muscle a little bit at a time.  If you try to take too much of the muscle at once you’re likely to damage nerves or arteries.

As you’re removing the muscle, look for the following structures:

Multiple branches of CN V3 run through the infratemporal fossa.  You’ve seen one in the oral cavity, the lingual n.  Another large one is the one you’ve (hopefully) successfully guarded from the saw, the inferior alveolar n.  The deep temporal nn. run along the bone of the skull and deep to the temporalis m. (they innervate the muscle).  The auriculotemporal n. runs posteriorly, ultimately providing sensory innervation to the skin on the side of the head around the ear.

Temporomandibular joint (TMJ) dysfunction, or TMJD, or TMD, is a broad term that covers pain and dysfunction of the muscles of mastication or the TMJ itself.  The current view of TMD is that it is not a single disorder, but a cluster of related disorders with multiple common and variously overlapping symptoms.  This is reflected in the variable definitions and terminologies used by physicians to discuss TMD.

The joint-space of the TMJ is divided by the articular disk, so that there are functionally two joints, an upper joint between the articular disk and the temporal bone, and a lower joint between the head of the mandible and the articular disk.

The initial phase of jaw opening occurs within the lower joint, as the head of the mandible rotates against the articular disk.  

But this rotation can only open the jaw so far, and the later phase of jaw opening involves the upper joint, as the head of the mandible and the articular disk translate (slide) forward on the temporal bone.  This movement also involves protrusion of the jaw, and is mainly due to the action of the lateral ptergoid m.  Abnormal movement of the articular disk is the cause of the “popping” or “clicking” sound that is characteristic of many types of TMD

The three most consistent and agreed-upon signs and symptoms of TMD are:

1. Pain and tenderness of the muscles of mastication and/or the TMJ.  Pain is typically both on palpation and during movement of the joint.  Pain is the defining feature of TMD.  The pain may originate from the muscles of mastication or from the joint.  Muscle pain is typically a result of abnormal/hyperactive muscle function, and is often accompanied by clenching of the jaw while awake, and grinding the teeth at night (bruxism).  Joint pain is most often due to degenerative joint changes (arthritis) or instability of the joint due to abnormal movement of the bones and/or articular disk.

2. Limited range of mandibular movement.  Due to pain and derangement of the joint (see below).

3. Noises from the joint during movement.  Noises may include clicking, popping, or a grating/grainding noise called crepitus.  Clicking and popping noises are most often due to derangement of the joint, which means the articular disk has moved into an abnormal position, and then “popped” back into normal position to allow a movement to occur.  Clicking/popping is usually heard during opening and closing, and most often toward the end of the movement, as the disk moves back into place.  If the disk does not move back into position it may cause the jaw to lock.  Crepitus is typically heard as a result of arthritic changes to the joint, and may be heard at any time during the chewing cycle. 
   Other, less common signs are headache, referred pain to the teeth, neck or shoulder, tinnitus (ringing of the ears), dizziness, and hearing loss.