Facial Nerve and Parotid Gland Anatomy: Lecture Notes

 Dr. Doaa Abo ElKhair Lecturer of Anatomy & Embryology Faculty of Medicine, Menoufia University Facial nerve ▪ It’s the seventh cranial nerve. ▪ Type: Mixed nerve (has sensory, motor & parasympathetic fibres). ▪ Exit from the brain: Exits at the junction between the pons and the me...

 Dr. Doaa Abo ElKhair Lecturer of Anatomy & Embryology Faculty of Medicine, Menoufia University Facial nerve ▪ It’s the seventh cranial nerve. ▪ Type: Mixed nerve (has sensory, motor & parasympathetic fibres). ▪ Exit from the brain: Exits at the junction between the pons and the medulla oblongata. Arises by 2 roots: - Motor root: large and contains motor fibres. - Nervus intermedius: small and contains both sensory and parasympathetic fibres. ▪ Course: A) Intracranial part of the facial N.: - The 2 roots of facial nerve enter the internal auditory meatus and unite at the bottom of the meatus. - The facial nerve enters the facial canal which takes a winding course through the petrous part of temporal bone. - It emerges from the skull through the stylomastoid foramen. B) Extracranial part of the facial N.: - After exiting from the stylomastoid foramen, it runs forwards to pierce the parotid gland. - Within the substance of the parotid gland, it lies superficial to the retromandibular vein and the external carotid artery. - Finally, it divides into its terminal branches which emerge from the anterior border of parotid gland and radiate across the face.  Branches of facial nerve Branches within the facial canal Terminal branches Branches after exit from the stylomastoid Greater Nerve to foramen superficial Chorda Tympanic stapedius petrosal tympani branches nerve Nerve to Posterior Nerve to Posterior belly of Stylohyoid auricular nerve digastric muscle. muscle. ▪ Branches: A) Branches within the facial canal: 1- Greater superficial petrosal nerve: - Joins the deep petrosal nerve to form the nerve of the pterygoid canal. - It transmits: Taste fibres: from the soft palate. Parasympathetic fibres: to the lacrimal, nasal and palatine glands (after relay in the pterygopalatine ganglion). 2- Chorda tympani: - Arises from facial nerve a short distance above the stylomastoid foramen. - Joins the lingual nerve a short distance below the skull. - It transmits: Taste fibres: from anterior 2/3 of tongue. Parasympathetic fibres: to the sublingual & submandibular salivary glands (after relay in the submandibular ganglion). 3- Tympanic branches: to the tympanic plexus. 4- Nerve to stapedius muscle: of the middle ear. B) Branches after exit from the stylomastoid foramen: 1- Posterior auricular nerve: supplies occipital belly of occipito-frontalis muscle. 2- Nerve to Posterior belly of digastric. 3- Nerve to Stylohyoid muscle. C) Terminal branches: Temporal – Zygomatic – Buccal – Mandibular – Cervical. These terminal branches supply: Frontal belly of occipito-frontalis muscle, facial muscles and platysma. ▪ Lesion: The lesion may be located at any level along the course of the facial nerve: Lesion of the facial nerve at the stylomastoid foramen is called “Bell's palsy”→ There is only motor loss of the same side of the face. ▪ Signs of Bell’s Palsy on the same side of the face: 1. Paralysis of the frontalis: inability to raise the eyebrow. 2. Paralysis of the orbicularis oculi: inability to close the eye or blink. 1 3. Paralysis of the buccinator: accumulation of food in 2 vestibule of the mouth. 3 4. Paralysis of the orbicularis oris: inability to whistle. 4 5 Saliva and food escape from the corner of the mouth. 5. Paralysis of the levators of the angle of the mouth: drooping of the angle of the mouth. Parotid gland ▪ Shape: The largest salivary gland. Nearly Mastoid pyramidal in shape. process ▪ Site: lies in a space which is bounded by: Anteriorly → the ramus of the mandible. Posteriorly → the mastoid process. styloid process Medially → the styloid process. Ramus of Superiorly → the external auditory mandible mastoid process meatus. stylomandibular Inferiorly → the stylomandibular ligament. ligament ▪ Relations: The parotid gland has: Base ✓ 3 surfaces → Parotid duct lateral – anteromedial – posteromedial. Posterior ✓ 2 borders → Anterior border border Apex anterior – posterior. Anteromedial surface Posteromedial surface ✓ 2 poles → upper (base) – lower (apex). Lateral surface A) Surfaces: Accessory 1- The lateral (superficial) surface: related to lobe Superficial parotid Parotid Skin duct lymph nodes Masseter Sternomastoid Superficial fascia containing platysma Great auricular nerve muscle and great auricular nerve. Anteromedial surface Superficial parotid lymph nodes. Medial pterygoid 2- The anteromedial surface: related to Ramus of mandible Ramus of the mandible & its attached Masseter muscles (Masseter, Medial pterygoid).  Internal jugular vein Styloid process 3- The posteromedial surface: related to Internal carotid artery Mastoid process and its attached Facial nerve muscles (Sternomastoid – posterior belly of digastric). Styloid process and its attached Mastoid process muscles (Stylohyoid – styloglossus – stylopharyngeus). Carotid sheath and its contents. B) Borders: 1- The anterior border: A convex border lying on masseter muscle. Come out of it (from above downwards): - Zygomatic branch of facial nerve. - Transverse facial artery. - Parotid duct and accessory lobe. - Buccal branch of facial nerve. - Mandibular branch of facial nerve. 2- The posterior border: A straight border parallel to the anterior border of sternomastoid muscle. C) Poles: 1- The upper pole (base): Concave upwards, surrounds the lower surface of external auditory meatus. Come out of it: - Temporal branch of facial nerve. - Superficial temporal vessels. - Auriculotemporal nerve. 2- The lower pole (apex): Tapering. Come out of it: - External carotid artery. - Anterior & posterior divisions of retromandibular vein. - Cervical branch of facial nerve. ▪ Structures within the substance of parotid gland: (arranged from deep to superficial): 1. The external carotid artery. 2. The retromandibular vein. 3. The facial nerve. ▪ Division: it is subdivided into: Superficial lobe → superficial to the facial nerve. Deep lobe → deep to the facial nerve. Accessory lobe → above the duct of the gland. Accessory lobe ▪ Nerve supply: 1- Sensory: The capsule → the great auricular nerve. The parenchyma → auriculotemporal nerve. 2- Parasympathetic (secretomotor): Otic ganglion Glossopharyngeal nerve → tympanic branch → tympanic plexus → lesser petrosal nerve → Otic ganglion → Postganglionic fibers to the gland. 3- Sympathetic (vasomotor): Nerve plexus around the ECA From the nerve plexus around the external carotid artery. ▪ Lymphatic drainage: 1- Superficial nodes (pre-auricular nodes): Lie superficial to the capsule of parotid gland. Drain into L.N. along the external jugular vein. 2- Deep nodes: Lie in the substance of parotid gland. Superficial nodes Drain into L.N. along the internal jugular vein. Deep nodes ▪ Parotid duct (Stensen's duct): Beginning: Appears at the anterior border of the parotid gland. Course: 5cm It runs forwards over the masseter muscle. At the anterior border of masseter, it curves medially piercing the buccal pad of fat, buccinator muscle and oral mucosa. Termination: It opens in the vestibule of the mouth, opposite the upper 2nd molar tooth. Surface anatomy: It is represented by the middle 1/3 of a line drawn from the tragus of the ear to a point midway between the ala of the nose and the angle of the mouth.  Clinical Notes: The facial nerve passes through the substance of the parotid gland; damage to the gland leads to paralysis of the muscles of expression on the same side of the face. Acute mumps is a viral disease affecting parotid capsule the parotid gland. Pain from the swollen gland is severe because it is enclosed by a tense non stretchable parotid capsule derived from the deep cervical fascia.  Clinical Notes: A stone lodged in the parotid Pain originating from the parotid gland is duct is another cause of often referred to the ear, temple or painful swelling of the gland. temporomandibular joint by the auriculotemporal branch of trigeminal nerve. Temple