(A) Intracranial part:
Facial nerve has 3 nuclei:
- Motor nucleus lies in pons.
- Superior salivatory nucleus: in pons, parasympathetic secretomotor to lacrimal, submandibular, and sublingual glands.
- Nucles solitarius: in medulla, sensory, carries taste sensation from the tongue.
Motor fibers form the motor root, while parasympathetic and sensory fibers join to form the sensory root (nervus intermedius).
The 2 roots emerge on the side of the brain stem, at junction between pons & medulla to cross CPA to I.A.M. Controlled by pyramidal & extrapyramidal fibers.
(B) Cranial (intratemporal) part:
- 37-45mm.
- Labyrinthine segment: runs in the I.A.C superior to VIII & anterior to superior vestibular nerve, runs laterally to medial wall at geniculate ganglion.
- Tympanic (horizontal) segment: starts at geniculate ganglion, curves to form 1st genu, runs backwards in medial wall till the posterior wall.
- Mastoid (vertical) segment: Runs inferiority (2nd genu), lies antero inferior to lat. SCC, then vertically downwards to leave skull at stylomastoid foramen.
(C) Extra cranial part:
Enters parotid gland >> divides into terminal motor branches.
Branches of Facial nerve
(1) In temporal bone.
a) Greater superficial petrosal: arises at geniculate ganglion >> secreto motor parasympathetic to lacrimal, nasal, palatine glands.
b) Nerve to stapedius: motor supply to stapedius.
c) Chorda tympani: exit just above stylomastoid foramen to enter ME >> carries taste from ant. 2/3 of tongue & secretomotor parasympathetic to sub lingual and sub mandibular glands.
(2) After exit from skull:
Two motor branches to stylohyoid & post belly of digastric.
Posterior auricular nerve: motor to occipital belly of occipitofrontalis.
(3) Five terminal branches in parotid:
Temporal, zygomatic, buccal, mandibular & cervical supply muscles of scalp, face, auricles & platysma.