Give the course if facial nerve in a flow chart manner
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Here is a detailed flowchart of the course of the facial nerve (CN VII), built from authoritative textbook sources:
Course of the Facial Nerve (CN VII) - Flow Chart
ORIGIN
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ NUCLEI IN THE PONS │
│ • Motor nucleus (lower pons) │
│ • Superior salivary nucleus (parasympathetic) │
│ • Nucleus tractus solitarius (taste/sensory) │
└─────────────────────────┬───────────────────────────────────────┘
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ SEGMENT 1: INTRACRANIAL SEGMENT (17-24 mm) │
│ • Exits ventrolateral pons │
│ • Travels through CEREBELLOPONTINE ANGLE (CPA) │
│ alongside CN VIII (vestibulocochlear nerve) │
│ and nervus intermedius │
│ • Blood supply: Anterior Inferior Cerebellar Artery (AICA) │
└─────────────────────────┬───────────────────────────────────────┘
│
▼
Enters INTERNAL AUDITORY CANAL (IAC)
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ SEGMENT 2: MEATAL SEGMENT (8-10 mm) │
│ • Runs in anterosuperior quadrant of the IAC fundus │
│ • Lies on superoanterior surface of CN VIII │
│ • Nervus intermedius lies between motor division & CN VIII │
│ • No major branches │
└─────────────────────────┬───────────────────────────────────────┘
│
▼
Enters MEATAL FORAMEN → FACIAL (FALLOPIAN) CANAL
⚠ Narrowest & most susceptible to inflammation
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ SEGMENT 3: LABYRINTHINE SEGMENT (4 mm) [SHORTEST] │
│ • Runs anterolaterally ABOVE the labyrinth │
│ • Almost at right angles to petrous pyramid │
│ • Reaches ► GENICULATE GANGLION │
│ (contains sensory perikarya of nervus intermedius) │
│ │
│ BRANCH: Greater Superficial Petrosal Nerve (GSPN) │
│ Exits at apex of geniculate ganglion │
│ → Travels under gasserian ganglion │
│ → Enters vidian canal → joins deep petrosal nerve │
│ → Forms VIDIAN NERVE │
│ → Pterygopalatine (sphenopalatine) ganglion (synapse) │
│ → Postganglionic → Lacrimal, nasal, palatine glands │
└─────────────────────────┬───────────────────────────────────────┘
│ 1st GENU (bend)
▼
┌─────────────────────────────────────────────────────────────────┐
│ SEGMENT 4: HORIZONTAL / TYMPANIC SEGMENT (11 mm) │
│ • From geniculate ganglion → 2nd genu │
│ • Runs backward, below & medial to │
│ horizontal (lateral) semicircular canal │
│ • Passes above oval window niche │
│ • No major branches │
└─────────────────────────┬───────────────────────────────────────┘
│ 2nd GENU (posterior bend inferiorly)
▼
┌─────────────────────────────────────────────────────────────────┐
│ SEGMENT 5: MASTOID / VERTICAL SEGMENT (13 mm) │
│ • From 2nd genu → stylomastoid foramen │
│ • Runs inferiorly through mastoid bone │
│ • Blood supply: middle meningeal artery (superficial branch) │
│ + stylomastoid branch of posterior auricular artery │
│ │
│ BRANCHES: │
│ ① Nerve to Stapedius muscle (near upper end) │
│ → Stapedius muscle (dampens sound/prevents hyperacusis) │
│ │
│ ② Chorda Tympani │
│ → Joins lingual nerve (CN V3) │
│ → Submandibular ganglion (synapse) │
│ → Submandibular & sublingual glands (secretomotor) │
│ → Taste: anterior 2/3 of tongue │
│ → Afferents → Nucleus tractus solitarius │
└─────────────────────────┬───────────────────────────────────────┘
│
▼
EXITS via STYLOMASTOID FORAMEN
│
▼
┌─────────────────────────────────────────────────────────────────┐
│ NEAR STYLOMASTOID FORAMEN (Extratemporal - proximal branches)│
│ │
│ BRANCHES: │
│ ③ Posterior Auricular Nerve │
│ → Occipitalis, posterior auricular, │
│ transverse & oblique auricular muscles │
│ │
│ ④ Digastric Branch │
│ → Posterior belly of digastric muscle │
│ │
│ ⑤ Stylohyoid Branch │
│ → Stylohyoid muscle │
└─────────────────────────┬───────────────────────────────────────┘
│
▼
Enters substance of PAROTID GLAND
│
▼
PES ANSERINUS
("goose's foot" - bifurcation)
┌────────────┴────────────┐
▼ ▼
UPPER (TEMPOROFACIAL) LOWER (CERVICOFACIAL)
DIVISION DIVISION
│ │
┌─────────┴──────┐ ┌─────────┴──────────┐
▼ ▼ ▼ ▼
① Temporal ② Zygomatic ③ Buccal ④ Marginal ⑤ Cervical
Branches Branches Branches Mandibular Branch
│ │ │ Branch │
Frontalis, Orbicularis Muscles of Depressor Platysma
corrugator, oculi, the upper lip anguli oris,
procerus lower lid & cheek lower lip
Summary of Key Segments
| # | Segment | Length | Key Landmark | Key Branch |
|---|---|---|---|---|
| 1 | Intracranial | 17-24 mm | CPA, IAC entry | - |
| 2 | Meatal | 8-10 mm | IAC fundus | - |
| 3 | Labyrinthine | 4 mm (shortest) | Geniculate ganglion | GSPN |
| 4 | Tympanic (Horizontal) | 11 mm | Medial to lateral SCC | - |
| 5 | Mastoid (Vertical) | 13 mm | Stylomastoid foramen | Stapedius nerve, Chorda tympani |
| 6 | Extratemporal | Variable | Parotid/pes anserinus | 5 terminal branches |
Branches - Mnemonic for Terminal Branches
"To Zanzibar By Motor Car"
- Temporal
- Zygomatic
- Buccal
- Marginal mandibular
- Cervical
Clinically Important Points
- Narrowest point = Meatal foramen (labyrinthine segment) - most vulnerable to inflammatory compression (e.g., Bell's palsy, Ramsay Hunt syndrome)
- Upper face bilateral innervation: Upper motor neuron lesions spare the forehead; lower motor neuron lesions affect the entire hemiface
- Lesion localization by testing: GSPN (lacrimation) > Stapedius nerve (hyperacusis) > Chorda tympani (taste) > Stylomastoid foramen (motor only)
- Blood supply: AICA (intracranial) → middle meningeal artery (intrapetrosal) → stylomastoid/posterior auricular arteries (extracranial)
Sources: Localization in Clinical Neurology 8e, p. 777-779; K.J. Lee's Essential Otolaryngology, p. 422
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