Head and Neck Lab 1B

Lab 1B: Parotid Region and Infratemporal Fossa

Learning objectives

Identify major arteries and veins of the face.
Locate and identify the 4 main muscles of mastication and temporomandibular joint (TMJ).
Understand the sensory territories of the nerves in the infratemporal fossa.

Short List of Structures - 1B

Removing the Skin from the Face and Scalp

Use a scalpel to remove the skin from the face and the scalp. The guide on the right shows the minimum area of skin you will need to remove to complete this lab, but eventually all of the skin will need to be removed.

You should include the external ear in the removal of the skin.

Take special care to remove only the skin. Realize that the muscles of facial expression attach to the skin of the face, making it very easy to remove these muscles with the skin.

Inferiorly, remove the skin of the mandible all the way down to where you stopped removing skin from the neck.

Laterally, remove the skin all the way to the posterior border of the ear, you can remove the ear if you wish.

Superiorly, remove the skin of the forehead and continue to remove the skin of the scalp as far back as you can at this time. Later in the lab you will turn the cadaver prone and remove the skin from the posterior part of the skull and the back of the neck.

Arteries and Veins of the Face

As you carefully dissect the face you will see the larger arteries and veins of the face.

Identify the facial a. which is a branch of the external carotid a. Follow its torturous (twisty) course into the face. Also look for the facial v., which follows the same general course as the facial a., but does not typically run in tandem with it.

The transverse facial a. is another branch of the external carotid. The transverse facial artery typically runs along a course from the ear toward the nose.

The superficial temporal a. is the last part of the external carotid a. It emerges anterior to the ear and travels superiorly and anteriorly to cover the temple region.

Arteries and veins of the face.

Arteries and veins of the face. 1 is the transverse facial artery and vein, 2 is the superficial temporal artery and vein, and the facial artery and vein are seen coming over the edge of the mandible.

Parotid Gland

Now we’ll move laterally and focus on the parotid region of the face.

The parotid salivary gland sits just anterior and inferior to the ear. Secretions from the parotid gland travel through the parotid duct, which pierces the buccinator muscles to empty into the oral cavity. The duct looks like a vein or an artery, and may have smaller pieces of glandular tissue along its length.

Two of the four large muscles of mastication (chewing) are visible adjacent to the parotid region, the masseter m. and the temporalis m. Both of these muscles have a big role in elevation of the jaw, which when done forcefully is the motion that powers chewing.

The masseter m. runs from the cheekbone down to the angle of the mandible. The parotid gland will lie over some of this muscle.

The temporalis m. attaches to a broad portion of the skull in the temporal region, and attaches to the mandible deep to the cheekbone and the masseter. The temporalis m. is broad and flat and lies deep to temporal fascia. You’ll have to reflect the temporal fascia to see the muscle beneath.

The muscles of mastication are innervated by the V3 branch of the trigeminal n., which also provides sensory innervation from the inferior part of the face.

The parotid region.

Main branches of the facial n.

Infratemporal fossa

Finally, we will dissect into the space that is deep to the ramus of the mandible; the infratemporal fossa. This will allow you not only to see the remaining muscles of mastication (pterygoids), but to better see terminal branches of the external carotid artery, and several branches of cranial nerves.

You should do this dissection on both sides of the head, but reflect the lateral pterygoid m. on one side only.

To begin, use blunt dissection and scissor spreading around the parotid gland to reveal both lateral borders of the masseter m., then cut this muscle superiorly where it attaches to the zygomatic arch so it can be reflected in the next step. You can do this by outlining the zygomatic arch with a scalpel.

Note that you do not need to cut the parotid duct as it says in the photo to the right, but you can if you find it is in the way.

Once the masseter m. has been cut, reflect it inferiorly and be sure to scrape its attachment off of the mandible until you can see bone (image on the right)

Then use a scalpel to finish superficially outlining the zygomatic arch, as shown with black dotted lines (image on the right)

You will then cut the zygomatic arch with a bone saw, as shown by the red dotted lines (image on the right).

You’ll make 3 cuts through the mandible as shown in the (both images on the right):

Through the coronoid process. The temporalis muscle attaches to the coronoid process.
Through the neck of the mandibular condyle.
Cut HALF WAY THROUGH the ramus of the mandible. Take care when making this cut to not cut all the way through, as the inferior alveolar n. runs along inside of the ramus of the mandible before entering the bone through the mandibular foramen. You will then break off this piece of bone with the Ronguer's (they look like pliers).
- This is very important, it is very easy to cut the inferior alveolar nerve with a bone saw cut that is too inferior or too deep
- Be sure to make the cut through the ramus of the mandible superiorly to help ensure that you don’t cut the inferior alveolar n. 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).

Structures in the superficial part of the infratemporal fossa.

Lateral pterygoid muscle removed to show structures in the deep part of the infratemporal fossa.

Once you’ve identified the lateral pterygoid m. you need to remove it from the infratemporal fossa to view deeper structures. Do this on one side of the head, and keep the lateral pterygoid intact on the other side. 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. One large nerve is 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.

The maxillary a. is the last branch of the external carotid a., and supplies blood to structures in the infratemporal fossa. One of the first branches of the maxillary a. is the middle meningeal a. The deep temporal aa. run with the deep temporal nn., and supply blood to the temporalis m. The inferior alveolar a. runs with the inferior alveolar n. and provides blood to the mandibular teeth.

Finally, have a look at the temporomandibular joint (TMJ). Cut away any remaining muscle tissue from the joint capsule, and make an incision in the joint capsule to reveal its contents. Sitting between the mandibular condyle and the articular area of the temporal bone is a thick fibrocartilagenous pad, the articular disk of the temporomandibular joint.

Clincal Correlations

Trigeminal Neuralgia (TN) or tic douloureux:

The trigeminal nerve (CN V) brings somatic sensation from the face, and provides somatic motor innervation to the muscles of mastication (but NOT facial expression, that’s the facial nerve, CN VII).

Trigeminal neuralgia is a condition in which nociceptive (pain) fibers within the trigeminal nerve fire and cause excruciating facial pain. These bouts of pain may last for seconds, minutes, or for several hours. In some cases the pain is associated with “trigger spots” on the face, and may be induced by very light touch or even air currents. In other cases the pain occurs spontaneously, with no apparent trigger. TN may have a devastating effect on the sufferer’s lifestyle, as they curtail normal daily activities for fear of initiating an episode.

The cause of the pain is currently thought to be pressure on the trigeminal nerve from an adjacent artery where the nerve exits the brainstem. It’s thought that TN may become worse through time as the pressure first causes pain due to simple compression, but with prolonged progression demyelination may occur that makes the pain episodes more frequent and longer-lasting, and less likely to be reversible. Therefore it’s thought that prompt treatment is critical to decrease the extent of the disease.

Sensory territories of the main sensory branches of CN V.

Intracranial course of CN V.

Bell’s Palsy:

Bell’s palsy is defined as an idiopathic paralysis of some or all of the muscles of facial expression, which makes it a disease that effects the facial nerve (CN VII). If facial paralysis is observed and a cause can be found (virus, trauma) the condition is no longer considered Bell’s palsy, because it is no longer idiopathic. Therefore Bell’s palsy is a diagnosis of exclusion; there is no definitive test for Bell’s palsy, but if no cause for the facial paralysis can be found the diagnosis is Bell’s palsy.

Symptoms typically occur rapidly, often showing up overnight, such that one wakes up and part or all of the face is paralyzed. Unilateral (one-sided) paralysis is most common. Even without treatment most Bell’s palsys improve. Return of function usually begins within 3 weeks, and complete return of function is typical.

Bell’s palsy is thought to occur due to inflammation of the facial nerve where it passes through a relatively long and narrow passage through the temporal bone. Inflammation in that tight space is thought to cause compression of the nerve, resulting in a temporary loss of function of the nerve.

Major branches of CN VII

CN VII passes through the petrous part of the temporal bone before emerging from the stylomastoid foramen.

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:

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

Lateral view of the left TMJ.

Lateral view of the left TMJ, showing the movements that occur during jaw opening.

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