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Home , Frontalis muscle, Occipitalis muscle, Occipitofrontalis muscle

FACE AND , MUSCLES OF FACIAL EXPRESSION, AND PAROTID GLAND (Grant's Dissector [16th Ed.] pp. 244-252; 254-256; 252-254)

TODAY’S GOALS: 1. Identify the parotid gland and parotid duct 2. Identify the 5 terminal branches of the facial (CN VII) emerging from the parotid gland 3. Identify muscles of facial expression 4. Identify principal cutaneous branches of the trigeminal nerve (CN V) 5. Identify the 5 layers of the scalp 6. Identify the , retromandibular vein, and external carotid within the parotid gland 7. Identify the auriculotemporal nerve and superficial temporal vessels

DISSECTION NOTES: General comments: Productive and effective study of the remaining lab sessions on regions of the head requires your attention to and study of the osteology of the . The opening pages of this section in Grant’s Dissector contains images and labels of the skull and parts thereof. Utilize atlases as additional resources to learn the osteology. Couple viewing of these images with an actual skull in hand (available in the lab) to achieve mastery of this material. Incorporate the relevant osteology to a synthesis of the area being covered.

This lab session introduces you to the face and scalp, the major cutaneous (branches of the trigeminal nerve [CN V]) that supply the skin of the face and scalp, and important muscles of facial expression. Some helpful overview comments to consider as you begin this study include: • The skin of the face is quite thin and mobile except where it is firmly attached to the nose and • Muscles of facial expression are located within the superficial • Muscles of facial expression act as sphincters and dilators around the mouth, eyes, and nostrils • Muscles of facial expression are innervated by terminal branches of the facial (CN VII) nerve: temporal, zygomatic, buccal, marginal mandibular, cervical • The parotid gland is the largest salivary gland and lies just in front of the and is drained by the parotid duct • Terminal branches of the facial nerve pass through the substance of the parotid gland and emerge along its borders

I. BONY LANDMARKS – Anterior View of the Skull for today’s lab (See Fig. 7.16, Dissector p. 245) - supraorbital foramen (notch) Maxilla - infraorbital foramen Zygomatic bone and zygomatic arch Mandible - mental foramen

Skin Incisions. Refer to Figs. 7.19 and 7.25 (Dissector pp. 248 and 255) for making skin incisions on the face and scalp (extend the midline cut “A” in Fig. 7.19 to “A” in Fig. 7.25 and make the cut from A to D in Fig. 7.25). Use a sharp scalpel and reflect only the dermis. Deep to the dermis, the superficial fascia is variable in thickness and contains fat, loose connective tissue, and the muscles of facial expression. Exercise care in removing the skin over the . It is the thinnest in the body. Refer to Fig. 7.21 (Dissector p. 250) to identify the general pattern of facial musculature before proceeding to dissect these muscles.

11 II. PAROTID GLAND, PAROTID DUCT, AND TERMINAL BRANCHES OF FACIAL NERVE – 5 major terminal branches (See Fig. 7.20, Dissector p. 249) Before getting too far along in today’s session you should first identify one or two terminal branches of the facial nerve so you get an idea of how large (or small) they are. Then, using blunt dissection with scissors and forceps, carefully remove fat and loose CT to identify muscles and branches of CN VII. The terminal branches of the facial nerve emerge from the borders of the parotid gland. The external surface of the parotid gland is triangular in appearance with its base located just inferior to the zygomatic arch and its apex extending into the neck below the angle of the mandible. The outer surface of the gland is covered by tough, deep fascia [investing fascia]. A portion of the gland overlays the (one of the ). Find the parotid duct emerging from its anterior border about 2 cm inferior to the zygomatic arch and follow it medially. Probe above or below the duct for the buccal branch(es) of VII that course medially to the muscles in the central part of the face. Trace these nerves back toward the parotid gland. Where they emerge from the gland, dissect the gland tissue superficial to these branches to expose them more clearly. The facial nerve divides the gland into a superficial and deep lobe.

Locate the terminal branches emerging from the parotid gland. • Temporal br – crosses the zygomatic arch in the direction of the • Zygomatic br – crosses the zygomatic bone toward the lateral corner of the eye to orbicularis oculi • Buccal br – may consist of a few branches that course medially superficial to the masseter muscle to muscles in the central part of the face in company with the parotid duct • Marginal Mandibular br – courses along the lower border of the mandible and superficial to the facial artery and vein as they ascend onto the face. Supplies the muscles of the lower lip and chin. • Cervical br – descends near the angle of the mandible into the neck to supply platysma

Remove the buccal fat pad (anterior and medial to the masseter and overlying the ) and observe the parotid duct. Follow it to where it pierces the buccinator muscle to enter the oral cavity. While probing through this fat, you may encounter the long buccal nerve (this is a sensory branch of the mandibular division of the trigeminal nerve that supplies the skin and mucosal lining of the cheek).

III. FACIAL ARTERY (branch of the external carotid) AND FACIAL VEIN These vessels appear on the face by crossing the lower border of the mandible at the anterior border of the masseter muscle. The facial vein should be observed just posterior to the artery. The artery has a tortuous appearance. Both vessels course superficial and deep to muscles in their ascent to the medial angle of the eye. In its course, the facial artery gives rise to inferior and superior labial (to lower and upper lips, respectively) and lateral nasal branches before ending as the angular artery.

IV. MUSCLES OF FACIAL EXPRESSION (Fig. 7.21, Dissector p. 250) Focus your dissection on the following muscles by identifying their location in an atlas and then carefully remove connective tissue overlying these delicate muscles: The platysma and buccinator have already been identified.

Muscles of the Mouth/Lips Muscles of the Eyelid Orbicularis oris Orbicularis oculi (orbital and palpebral parts) Zygomaticus major Depressor labii inferioris Depressor anguli oris Buccinator See clinical note on facial nerve and Bell’s palsy (Dissector p. 251)

12 V. LOCATION OF MAJOR SENSORY NERVES OF THE TRIGEMINAL NERVE SYSTEM The trigeminal nerve (CN V) supplies most of the skin of the face and scalp. The trigeminal nerve has three divisions, V1, V2, and V3. Each division supplies sensory innervation to specific portions of the face (see Fig. 7.22, Dissector p. 251). The cell bodies of these sensory neurons are located in the trigeminal (semilunar, Gasserian) ganglion within the middle cranial fossa.

Divisions of CN V Major Cutaneous Nerves Supplying the Face V1 = Ophthalmic V2 = Maxillary Infraorbital nerve V3 = Mandibular Mental nerve Identify these nerves where they exit foramina of the same name as follows (refer to a skull or illustration on p. 245, Fig. 7.16):

• Supraorbital nerve, artery, and vein – Make a 3 inch long horizontal incision down to the bone about two inches above the medial half of the bony orbit. Then, make two vertical incisions at each end of the horizontal incision that are directed to the medial end and midpoint, respectively, of the bony orbit. Reflect this inverted “U”-shaped flap inferiorly and observe the supraorbital neurovasculature exiting its foramen or notch. • Infraorbital nerve, artery, and vein – Identify the levator labii superioris muscle and palpate the sharp inferior orbital margin. Place a probe beneath the LLS at its attachment just below the orbit and cut down to the probe. Reflect the muscle inferiorly to reveal the foramen and its neurovasculature exiting. • Mental nerve, artery, and vein – Make a full thickness cut through the midline of the lower lip and chin and another full thickness cut through the corner of the mouth. Cut through the mucosal attachment to the mandible and draw this flap inferiorly to expose the neurovasculature exiting the mental foramen.

VI. SCALP The scalp consists of 5 layers: Skin, subCutaneous tissue, Aponeurotic (containing the frontal and occipital bellies of the ), Loose connective tissue, and Periosteum (the soft tissue membrane covering bone). Attempt to find these layers: Skin – thick and firmly attached to the underlying superficial fascia Subcutaneous tissue or superficial fascia – tough, coarse tissue that contains abundant collagen fibers that attach to the external surfaces of blood vessels in this layer. These fibers hold the vessel open when cut, which explains the profuse bleeding by lacerations to the scalp. The nerve and blood supply to the scalp course in this layer. (See Fig. 7.27, Dissector p. 256) – the frontalis muscle consists of two bellies (see Fig. 7.26, Dissector p. 255) that attach anteriorly to the skin of the and and posteriorly to the epicranial (galea) aponeurotica, the tough connective tissue sheet that connects the frontal and occipital bellies. The also consists of two bellies that attach to the superior nuchal line posteriorly. The first three layers are tightly fused and move as a single unit over the 4th layer of loose connective tissue. Loose connective tissue – contains less dense connective tissue and may be a source of spread of infectious materials or blood that enters this space; for this reason, it is often referred to as the “danger zone.” Periosteum – the outer soft tissue covering of the calvarium.

VII. DEEP RELATIONSHIPS WITHIN THE PAROTID GLAND/PAROTIDECTOMY

DISSECTION NOTES: General comments: The external surface of the parotid gland is triangular in appearance, however, the gland is actually wedge-shaped gland and extends posterior and deep to the ramus of the mandible. The focus of the next phase of dissection is to preserve the terminal branches of the facial nerve previously 13 identified and to remove the remainder of the parotid gland in a piece-meal fashion to identify the retromandibular vein and external carotid artery that course within the substance of the gland. A thorough “cleaning” of the parotid bed is essential preparation for the next lab study of the infratemporal region. Familiarize yourself with the relevant osteology of this region before proceeding with the dissection.

I. Osteology of Parotid Region (Dissector p. 252, Fig. 7.23) A. Bony landmarks 1. • External auditory meatus • Mastoid process • Styloid process • Stylomastoid foramen • Mandibular fossa 2. Mandible • Head • Neck • Ramus • Angle B. Boundaries of parotid bed • Posteriorly: Mastoid process and posterior • Anteriorly: Ramus of mandible; masseter (laterally); medial pterygoid (medially) • Medially: Styloid process; stylopharyngeus, stylohyoid, and muscles • Superiorly: Undersurface of external auditory meatus and capsule of temporomandibular joint

II. Dissection Instructions and Structures to Locate A. Piece-meal parotidectomy – First, identify and protect the parotid duct and branches of the facial nerve. Follow these structures into the gland and remove overlying gland tissue in a piece- meal fashion using scissors and forceps. Then, proceed to remove the deeper portions of the gland. The facial nerve should appear as a single nerve structure where it emerges from the stylomastoid foramen. Deep to the facial nerve find the retromandibular vein and the external carotid artery.

B. Identify within the gland: (Dissector p. 253, Fig. 7.24) • Facial nerve • Retromandibular vein: Formed by union of the maxillary and superficial temporal veins • External carotid artery: Terminates near the neck of the mandible by dividing into the maxillary and superficial temporal arteries

• Auriculotemporal nerve (branch of CN V3) – emerges between the external auditory meatus and head of the mandible. It ascends into the scalp on the side of the head by crossing the root of the zygomatic arch. This nerve is located posterior to the superficial temporal vessels. It provides sensory innervation to the temporomandibular joint, the anterior portion of the ear, and the scalp over the temporal region. It also conveys postganglionic parasympathetic fibers to the parotid gland.

14 PEER TEACHING GUIDE: 1. Demonstration of the parotid gland and the parotid duct. 2. Demonstration of the 5 terminal branches of the facial nerve emerging from the borders of the parotid gland. 3. Demonstration of the listed muscles of facial expression. 4. Demonstration of the location and major cutaneous branches of the trigeminal nerve (CN V). 5. Demonstration of the 5 layers of the scalp. 6. Demonstration of the boundaries and relationships of the parotid bed. 7. Demonstration of the facial nerve within the parotid bed. 8. Demonstration of the retromandibular vein and external carotid artery and their terminal branches. 9. Demonstration of the auriculotemporal nerve.

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