Introduction

In this lab, you will explore the muscles and vasculature of the neck and face. These muscles allow us to express emotions from happiness to sadness, surprise to anger. The structures discussed in this lab have a range of clinical implications, from the scalene muscles placing pressure on neurovascular structures to vascular compromise that can be fatal.

Lab Activity 1: Visible Body – Muscles and Vasculature of the Neck

Use the Visible Body app on the iPad to observe the muscles and vasculature of the neck.

Muscles of the Neck

• In the iPad Atlas App, go to the Regions tab and click on 1. Head and Neck. Now, remove all of the systems (lymphatic, nervous, circulatory…etc.) except for the skeletal and muscular from the sidebar.
• First, click on the Platysma muscle and hide it (you will learn about it as a muscle of facial expression later in the lab). Just deep to the platysma, you can observe the sternocleidomastoid muscle. This muscle runs from the sternum and clavicle to the mastoid process of the temporal bone. It is primarily innervated by CN XI, the accessory nerve. When only one side contracts, it causes rotation of the head to the opposite side of the muscle that is contracting. Try palpating your sternocleidomastoid muscles and rotate your head from side to side. The more you rotate your head to the opposite side, the more this muscle becomes prominent in the anterolateral portion of your neck. Bilateral contraction contributes to flexion of the neck.
• Rotate the images, so you are looking at a posterior view of the neck. Click on the Trapezius, hide it, & observe the splenius capitis. Bilateral contraction of this muscle causes extension of the neck. Unilateral contraction (contraction of this muscle on only one side) can cause lateral flexion of the neck to the same side or rotation to the same side.
• Rotate the image to an anterolateral view and observe the anterior, middle, and posterior scalene muscles. To get a better view of these muscles, you may want to hide the sternocleidomastoid muscle. The scalene muscles run from the cervical vertebrae to the first and second ribs. Their primary action occurs with breathing. They act to elevate the ribs during forced inspiration. Unilateral contraction of these muscles also contributes to lateral flexion of the neck to the same side and rotation of the neck to the opposite side.
• Rotate the image to a lateral view and observe the hyoid bone. This bone is inferior to the mandible within the neck. The hyoid is suspended within the neck by muscles and provides an important site of attachment for them.
• Now rotate the image to a more anterior view and observe the infrahyoid muscles. As the name implies, these muscles are located inferior to the hyoid. The names of these muscles indicate the attachment points for these muscles. Together these muscles anchor the hyoid and depress both the hyoid and larynx during swallowing and speaking.
  • Observe the omohyoid. This muscle is digastric, meaning that it has two muscle bellies. Observe the short, intermediate tendon between the superior and inferior muscle bellies. This tendon is held to the clavicle by a fascial sling. The word part “omo” means scapula, and this muscle runs from the scapula to the hyoid bone.
  • View the sternohyoid. This muscle runs from the sternum to the hyoid.
  • Two additional muscles of this region are deep and visible when you hide the platysma, sternocleidomastoid, omohyoid, and sternohyoid. The sternothyroid and thyrohyoid run from the sternum to the thyroid cartilage and thyroid cartilage to the hyoid bone, respectively. We will discuss the thyroid cartilage with the larynx later in this unit, but you can highlight this cartilage superior to the trachea.

• Move the image so you can see under the chin (view from inferior to superior) and observe the suprahyoid muscles. These muscles are superior to the hyoid, and all have an attachment site on the hyoid. As a group, these muscles form much of the floor of the mouth and elevate the hyoid and larynx in swallowing and speaking.
  • Observe the digastric muscle. Note, don’t confuse this with the omohyoid, despite their similar appearance. The anterior belly of the digastric runs from the mandible to the hyoid bone, and the posterior belly of the digastric runs from the hyoid bone to the temporal bone (near the mastoid process).
  • Superior to the posterior belly of the digastric, observe the stylohyoid. This muscle travels from the styloid process of the temporal bone to the hyoid.
  • The mylohyoid can be seen just inferior and medial to the mandible. This muscle runs from the mandible to the hyoid and forms the anterior floor of the mouth.
  • In order to observe the geniohyoid, you will have to hide the mylohyoid. This muscle runs from the mandible to the hyoid bone as well, but it is smaller and sits deep to the mylohyoid. You may need to rotate the image slightly posteriorly to observe this muscle.

From the home screen in the Visible Body Atlas, click on the Systems tab and then go to Circulatory System Views and click on 5. Carotid and Jugular to show the arteries of the head and neck:

• In a right anterolateral view, observe how the brachiocephalic trunk divides into the subclavian and common carotid arteries (you may want to fade or hide brachiocephalic, internal jugular and subclavian veins). On the left side of the body, these two arteries branch directly off the aortic arch. Follow the subclavian artery laterally for a short span and observe the vertebral artery. This artery travels superiorly through the transverse foramen of the cervical vertebrae to supply the brain. You have already viewed this artery as it comes together to form the basilar artery when you studied the circle of Willis.
• Now observe the common carotid artery. This artery travels superiorly through the neck and branches into the internal and external carotid arteries. You will want to hide the mandible to see these arteries better. The internal carotid artery continues superiorly without branching in the neck, travels through the skull, and provides the majority of the blood supply to the brain.
• The external carotid artery supplies blood to the scalp, the face, and some structures of the neck. Six arteries branch from the external carotid artery before it terminates and divides into two arteries. To observe several of these arteries through their whole path, you will need to rotate the image back and forth. You may also want to zoom in on the branches. Observe the following arteries as they branch from the external carotid arteries, in order from inferior to superior:
  • Ascending pharyngeal artery: This is not visible in the app, and you will not be asked to identify it on the exam. This artery ascends to supply the pharynx, middle ear, and cranial meninges.

• • Superior thyroid artery: Runs inferiorly to supply the thyroid gland and larynx.
  • Lingual artery: Observe how this artery runs medially to supply the tongue.
  • Facial artery: This artery branches just superior to the lingual artery. In fact, sometimes the facial and lingual arteries branch from the external carotid artery as a common trunk before dividing. It travels along the inferior aspect of the mandible and then wraps around the middle portion of the mandible and ascends through the face. It supplies the submandibular gland, lips, and muscles of the face.
    • Angular artery: This terminal branch of the facial artery runs along the nose to the medial corner of the eye.
  • Occipital artery: This artery arises from the posterior aspect of the external carotid artery and travels superiorly and posteriorly to supply the posterior scalp and neck.
  • Posterior auricular artery: This artery arises from the posterior aspect of the external carotid artery just superior to the occipital artery. It ascends just anterior to the mastoid process of the temporal bone and posterior to the ear, and it supplies muscles of this region, the parotid gland, and part of the scalp.
  • Superficial temporal artery: The external carotid artery terminates as it divides into the superficial temporal artery and maxillary artery. The superficial temporal artery travels superiorly to supply part of the scalp and superolateral face.
  • Maxillary artery: This is the primary artery supplying the deep structures of the face. It travels anteriorly and medially and gives branches that supply parts of the external ear, the cranial cavity, the scalp, the mouth (including the cheek, teeth, upper and lower jaw, palate, and gums), and the inferior portion of the orbit.

Go back to the home screen in the Visible Body Atlas and click on the Systems tab, then Circulatory System Views and click on 5. Carotid and Jugular to show the veins of the head and neck:

• Now click on the external jugular vein, which empties into the subclavian vein. This vein drains part of the lateral aspect of the head.
• The internal jugular vein ultimately drains the majority of the blood from the head and neck. The internal jugular vein joins with the subclavian vein to form the brachiocephalic vein. Unlike the arteries of the same name, this happens on both the right and left side. This is because they both need to carry their blood toward the midline to reach the superior vena cava. However, for the arteries on the left side, the arch of the aorta already travels towards the left, positioning the subclavian and common carotid arteries in the appropriate place where they would normally branch.

**Note: All of these muscles are innervated by the facial nerve (CN VII) except for levator palpebrae superioris, which is innervated by the oculomotor nerve (CN III).

^This is the longest name of a muscle in the body.

Use the Navigator to observe the structures described above and listed in the list of terms. Use the presets and observe the vasculature. Then use the advanced view window to add or remove muscles and vessels from the image. This tool can be very helpful for viewing the muscles and vasculature from different angles as well as for isolating the muscles and vasculature. DO NOT save any pre-sets.

If you are having difficulty seeing the vessels, you can change the background color of the Navigator screen. Click on File and then Preferences. Here you can choose a lighter background color.

Lab Activity 4: Plastinated tissue

Observe the muscles of the face and neck and hyoid bone on the head and neck and respiratory plastinated tissue.

On the head and neck plastinate:

• First observe the hyoid bone. It is difficult to see, but part of it can be seen/palpated just deep and inferior to the mandible. You can notice that several muscles are inserting into it from superior and inferior directions.
• Now observe the sternocleidomastoid. While its origin is not present in this model, the bulk of the muscle and its insertion at the mastoid process are visible.
• On the posterior aspect, observe the splenius capitus.
• Laterally, observe the anterior, middle, and posterior scalenes.
• Now look at the suprahyoid muscles. The anterior and posterior bellies of the digastric can be easily observed, with the common middle tendon being held to the hyoid bone. Mylohyoid sits just deep to the anterior belly of the digastric. Stylohyoid is very skinny and sits just deep to the posterior belly of the digastric. The geniohyoid is not visible here because it is deep to the mylohyoid.
• Now look at the infrahyoid muscles. Only the superior belly of the omohyoid is visible here. Sternohyoid is also visible, but it is cut before it reaches the sternum. However, you can tell it is the sternohyoid because it runs past and does not insert into the thyroid cartilage. Thyrohyoid and sternothyroid are visible, but they are better seen on the respiratory plastinate.
• Observe the muscles of facial expression on this plastinate. Not all muscles are visible. For example, the occipitofrontalis may have some visible fibers, but part has been cut, and the epicranial aponeurosis is not visible. However, you should be able to identify most of them. Be sure to observe the direction of the muscle fibers and think about the actions that these muscles perform.

On the respiratory plastinate:

• The thyrohyoid is more easily visible on this model. Several other muscles described above can be seen here as well.
• Observe the muscles of facial expression that are visible on this specimen. Again, not all of them will be visible, but you should be able to identify most of the muscles of facial expression between the two specimens.