Lab 1A
Face and Posterior Neck

Removing the skin from the face

Be careful removing the skin of the face. The muscles of facial expression, which are very thin, lie directly underneath and are attached to the skin and thus are easily damaged. Take your time.

However, even with careful dissection you are unlikely to be able to identify more than a few of the numerous muscles of facial expression.

You should remove the skin from the face and the scalp.

There will be significant variation in the definition and therefore the “dissectability” of the facial muscles among the cadavers. Find as many muscles as possible. Do not expect to find every muscle on the diagram. The listed muscles are those you are most likely to find. Take some time to tour other tables with an eye toward seeing additional muscles of facial expression.

• Frontal belly of the occipitofrontalis m. (1)

• Orbicularis oculi m. (3)

• Zygomaticus major m. (7)

• Zygomaticus minor m. (8)

• Orbicularis oris m. (10)

• Depressor anguli oris m. (13)

• Mentalis m. (15)

• Buccinator m. (16)

As you work to clean up the muscles take care to preserve any arteries, veins, and nerves you come across. We’ll deal with those structures in the next few pages.

Arteries and veins of the face:

As you carefully dissect the face and work to define some of the muscles of facial expression, you will also see the larger arteries and veins of the face.

Hopefully you identified the facial a. during dissection of the superior neck. 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.

Somatic sensory (general sensory) innervation of the skin of the face, as well as the deep structures of the face, is by the trigeminal n. (CN V). The trigeminal (literally “three twins”) nerve has 3 main divisions, which are referred to as V1, V2, and V3, for the first, second and third branch of V. You’ll also see them listed as V¹ or V₁. They also have proper names, V1 = ophthalmic n., V2 = maxillary n., and V3 = mandibular n.

Cutaneous nerves of these 3 main branches emerge from foramina of the skull:

• V1 from the supraorbital foramen

• V2 from the infraorbital foramen

• V3 from the mental foramen

You will look for the largest of these branches. They are cutaneous nerves, so finding more than the main stumps of the nerves will be challenging. While you will only see some subset of the nerves listed here, make sure you understand the pattern of innervation. Note that the posterior aspect of the scalp, and the neck, get their sensory innervation by branches of the cervical plexus.

You’ll need to scissor-spread through soft tissue on the face to get down to the foramina in the bone and find the cutaneous branches of CN V.

The cutaneous branches of V1 you will see are the supraorbital n. and the supratrochlear n., which exit the supraorbital foramen and supratrochlear foramen of the skull just superior to the orbit. The supratrochlear n. is smaller than, and medial to, the supraorbital n. These two nerves, along with a few more even smaller nerves, provide sensory input from the forehead to the superior part of the orbit, and the median strip of skin on the nose.

The infraorbital n. is the main cutaneous branch of V2. It exits the infraorbital foramen and provides sensory input from the inferior part of the orbit to the upper lip and laterally out to the cheekbone.

The largest cutaneous branch of V3 is the mental n., which exits the mental foramen and provides sensory input from the lower jaw and superiorly to the anterior part of the external ear.

As you can see from the figures, there are multiple smaller branches of CN V that emerge from smaller foramina in the skull. We’re focusing on the 4 largest branches, because we have the best chance of actually finding them, and because they provide examples of cutaneous branches of V1, V2, and V3. But be aware that the infraorbital n. is not the only cutaneous branch of V2, and the mental n. is not the only cutaneous branch of V3.

Also realize that the deeper parts of the trigeminal nerve branches provide somatic sensory information from the nasal and oral cavities. For example the superior and inferior alveolar nerves carry general sensation from the teeth of the upper and lower jaws. When you get some small particle in your nose, you’re aware of that due to a branch of V2 that provides general sensation from the nasal cavity.

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.

You may have already seen evidence of the final structure we’ll search for in the parotid region, the facial n. (CN VII). The facial n. provides motor innervation to muscle of facial expression. The facial n. exits the skull through the stylomastoid foramen (a hole between the styloid process and the mastoid process) and as it passes through the substance of the parotid gland it branches into 5 main branches (or groups of branches), and those branches are named according to the region of the face they travel to:

• Temporal branch(es) of the facial n.

• Zygomatic branch(es) of the facial n.

• Buccal branch(es) of the facial n.

• Mandibular branch(es) of the facial n.

• Cervical branch(es) of the facial n.

The mnemonic to remember these is
To Zanzibar By Motor Car
Like most mnemonics, it’s kind of stupid , but effective.

As these branches travel from the parotid gland out onto the face they become very thin, so many of the terminal branches may have been destroyed during your dissection of the face. Within the parotid gland, however, the branches are typically large enough to identity. Carefully scissor-spread and dissect your way down into the parotid gland, and try to find large branches of the facial n., and the main stem of the facial n.

Note that the sensory and motor innervation of the face are from different cranial nerves. The trigeminal nerve carries general sensation from the superficial and deep parts of the face. The facial nerve provides motor innervation to the muscles of facial expression.

Triangles of the neck...

The neck is often divided into a series of “triangles”. There is a lot of stuff in the neck, and dividing it into pieces and then subdividing those pieces even further may be a useful tool in order to “divide and conquer” the anatomy.

We will define and use the triangles of the neck as an organizational tool. You are likely to hear references to the triangles clinically, as many clinicians use the terminology e.g., to describe where a tumor is palpable or where an incision should be made. However you will not be held responsible (on an exam) for the borders or contents or even names of any of the triangles. If they’re helpful as an organizing or study tool please do use them, but we will not test you on them.

Brachial plexus and the scalene muscles in the posterior triangle of the neck:

Concentrate on cleaning up the investing fascia and any other connective tissue or cutaneous nerve branches that obscure your view of the posterior triangle of the neck.

Work your way into the inferior part of the posterior triangle (down toward the clavicle, or where the clavicle used to be) and find a large nervous system structure, the brachial plexus. The brachial plexus consists of the ventral rami of C5-T1. They form a bundle as they exit the neck and move laterally and inferiorly toward the root of the upper limb. We will work out the details of the brachial plexus during dissection of the limbs, but for now the plexus serves as a convenient landmark for identifying muscles in the posterior triangle of the neck.

The brachial plexus emerges between two of the three scalene muscles:

• Just anterior to the brachial plexus is the anterior scalene m. The phrenic n. typically lies on the surface of the anterior scalene m.

• Posterior to the brachial plexus is the middle scalene m.

• The posterior scalene m. is posterior and slightly inferior to the middle scalene m.

The final muscle found in the posterior triangle of the neck is actually only half of a muscle, the inferior belly of the omohyoid m. The omohyoid m. consists of two bellies separated by a tendon in the middle of the muscle. The inferior belly attaches to the scapula and runs superomedially. The intermediate tendon is fixed in place by connective tissue. The superior belly runs from the intermediate tendon superiorly, and attaches to the hyoid bone. The SCM covers the middle part of the omohyoid, but parts of both bellies can be seen with the SCM in place

As we continue to move posteriorly we come to muscles of the posterior triangle that are better seen from a posterior view (turn the cadaver prone and place a wooden block under the chest). Posterior and slightly superior to the middle scalene m. is the levator scapulae m., which you first saw during dissection of the back and shoulder region. The spinal accessory n. (CN XI) typically lies on the surface of the levator scapulae m., as it courses out to innervate the trapezius m. A clear view of the levator scapulae can be had by putting the cadaver in the prone position and fully reflecting the trapezius muscle, as on the right side of the figure below.

Medial to the levator scapulae m. is another long, straight muscle, the splenius capitis m., which runs from the spinous processes of the cervical vertebrae to the skull.

The final muscle found in the posterior triangle of the neck is actually only half of a muscle, the inferior belly of the omohyoid m. The omohyoid m. consists of two bellies separated by a tendon in the middle of the muscle. The inferior belly attaches to the scapula and runs superomedially. The intermediate tendon is fixed in place by connective tissue. The superior belly runs from the intermediate tendon superiorly, and attaches to the hyoid bone. The SCM covers the middle part of the omohyoid, but parts of both bellies can be seen with the SCM in place.

Overview

We’ll get started on brain removal today by performing the cervical laminectomy. You did a thoracic laminectomy during the thorax block.

Brain removal will continue in the next lab.

Cervical laminectomy: you will expose the cervical spinal cord by removing the lamina of the cervical vertebrae.

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.

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.