Muscles and Nerves: Trigeminal Nerve Quiz

Superficial Face Anatomy

• The superficial face is comprised of facial features, muscles of facial expression, perfusion and drainage patterns, the parotid gland, and its innervation.
• Skin landmarks include the glabella, philtrum, nasolabial folds, mentolabial folds/sulcus, labial commissure, oral fissure, and nasal ala.

Learning Objectives

• List the muscles of facial expression and describe their actions: Understand the significance of these muscles in controlling orbital, nasal, and oral openings, and the role of the SMAS.
• Detail the trigeminal nerve's divisions: Describe the axons, foramina traveled through, branches supplying sensation to the superficial face. Also, note their relationships with other structures.
• Define trigeminal and geniculate ganglia: Understand their specific functions and definitions.
• Describe the pathway of the facial nerve through the skull: Outline its path from the brain, its exit from the skull, and the naming of its branches to the face.
• Describe the external carotid artery branches and internal jugular tributaries: Describe their branching patterns and contributions to facial blood supply and venous drainage.
• Identify the parotid gland and duct: Determine the location of these structures and, importantly, the structures that pass through the gland, along with the autonomic innervation.

Facial Features overview

• Facial features and fascia
• Muscles of facial expression
• Perfusion and drainage patterns
• Parotid gland
• Innervation

Facial Muscles of Expression

• Lie within superficial fascia.
• Originate from bone (or deep fascia) and insert into skin (or other facial muscles).
• Anchored to skin via SMAS.
• Exhibit emotion and control facial openings (sphincters).
• Innervated by branches of the facial nerve.
• Organized into groups: epicranial, circumorbital & palpebral, nasal, and buccolabial.

Muscles of Facial Expression (specific groups)

• Epicranial group: occipitofrontalis & temporoparietalis.
• Circumorbital & palpebral group: orbicularis oculi, corrugator supercilii & levator palpebrae superioris.
• Nasal group: procerus, nasalis & dilator naris anterior.
• Buccalabial group: elevators, evertors, depressors of the lips, orbicularis oris & buccinator.
  • Zygomaticus major, zygomaticus minor, risorius, depressor anguli oris and depressor labii inferioris, mentalis.
• Buccinator muscles: chewing/expelling air from cheeks during activities like blowing or chewing, and speaking
• Platysma

Additional Facial Muscles (not facial expression)

• Masseter
• Temporalis

Parotid Gland

• Largest salivary gland.
• Location: anterior to the external ear, superficial to the masseter muscle/ramus of the mandible, extends between zygomatic arch & angle of mandible.
• Structures passing through the parotid gland: facial nerve proper & its branches, auriculotemporal nerve, external carotid artery, superficial temporal vessels, transverse facial vessels, maxillary vessels, and retromandibular vein.
• Salivary gland neoplasms account for 2-6% of head & neck neoplasms. Most (80-90%) are benign. Treatment is typically parotidectomy (total or partial).

Mumps

• Viral infection affecting major salivary glands.
• Initial symptoms similar to the flu, swelling of the glands is the key symptom.
• Prevention via MMR vaccine (~86% effective).

Parotid Duct

• Also called Stenson's duct.
• Travels over the masseter muscle.
• Opens into the oral cavity at the parotid papilla.

Facial Blood Supply and Venous Drainage

• Blood Supply: Predominantly from branches of the external carotid artery (ECA). Includes superior thyroid, ascending pharyngeal, lingual, facial, occipital, posterior auricular, maxillary, and superficial temporal arteries, some contributions from internal carotid artery (ICA).
• Branches of Facial A.: Superior & inferior labial arteries, angular artery.
• Superficial temporal artery and transverse facial artery.
• Venous Drainage: Facial vein continues as angular vein, joining with ophthalmic veins (entering the cavernous sinus). The retromandibular vein merges with the superior and inferior divisions. Retromandibular vein empties into the internal jugular or external jugular regions.
• Danger Triangle: Region on the face that if infected, cavernous sinus infection is possible. Covers area from upper lip to bridge of nose.

Facial Nerve Innervation

• Key concept: provides motor innervation to muscles of facial expression (SVE).
• Arise from pons/geniculate ganglion.
• 6 main branches; Posterior auricular, Temporal, Zygomatic, Buccal, Mandibular, and Cervical.
• Posterior Auricular: does NOT enter parotid gland
• Temporal branches: Frontalis, orbicularis oculi, corrugator supercilii
• Zygomatic branches: Orbicularis oculi, Zygomaticus major & minor
• Buccal branches: Orbicularis oris, buccinator, risorius.
• Mandibular branches: Mentalis, depressor labii inferioris, depressor anguli oris.
• Cervical branches: Platysma.

Trigeminal Nerve

• Largest cranial nerve (CN V) found pons; trigeminal (semilunar) ganglion in middle cranial fossa.
• Sensory components: involved in sensation of face (GSA), & motor in mastication (SVE)
• Three divisions from the ganglion; Ophthalmic V1, Maxillary V2, and Mandibular V3.
• Ophthalmic V1: exits via superior orbital fissure, branches include nasociliary, frontal, and lacrimal.
• Maxillary V2: exits via foramen rotundum, branches include zygomatic nerve (zygomaticofacial and zygomaticotemporal), and infraorbital nerve.
• Mandibular V3: exits via foramen ovale, branches include mental nerve, buccal nerve, and auriculotemporal nerve.
• no direct parasympathetic fibers.

Glossopharyngeal Nerve

• Arise from the medulla exits via jugular foramen.
• Functional components: GSA, GVA, SVE, GVE, SVA.
• GVE originates as fibers from inferior salivary nucleus.
• Innervates, the parotid gland.
• Lesser petrosal nerve: travels through foramen ovale; carries preganglionic parasympathetic fibers to the otic ganglion; postganglionic fibers innervate parotid gland.
• Preganglionic sympathetic nerves from lateral horn of T1-T2 hitchhike on ECA branches to reach the gland.
• Important branches include lesser petrosal, tympanic, lingual and pharyngeal nerves