Facial Nerve

Facial Nerve

Introduction

Mixed nerve

 Functional component :

SVE-  Muscles of face and scalp, stapedius muscle, posterior belly of digastric and stylohyoidmuscles    

GVE-  Secretomotor fibers to Submandibular  sublingual salivary glands, the lacrimal gland, and glands of nose and palate

SVA-  Taste from anterior two-thirds of tongue, from floor of mouth and palate

GSA- carry general sensation from concha

Facial Nerve Nuclei

 Main motor nucleus:

Lies in the lower part of the pons

The part of the nucleus that supplies the muscles of the upper part of the face receives corticonuclear fibers from both cerebral hemispheres

part of the nucleus that supplies the muscles of the lower part of the face receives only corticonuclear fibers from the opposite cerebral hemisphere

 parasympathetic nuclei –

They are the superior salivatory and lacrimal nuclei

 lie posterolateral to the main motor nucleus.

  sensory nucleus-

is the upper part of the nucleus of the tractus solitarius

taste travel through the peripheral axons of nerve cells situated in the geniculate ganglion

The central processes of these cells synapse on nerve cells in the nucleus

Efferent fibers cross the median plane and ascend to the ventral posterior medial nucleus of the opposite thalamus

Course

consists of a motor and a sensory root

 The fibers of the motor root first travel posteriorly around the medial side of the abducent nucleus

They then pass around the nucleus beneath the colliculus facialis in the floor of the fourth ventricle and, finally, pass anteriorly to emerge from the brainstem

 Sensory root (nervus intermedius) is formed of the central processes of the unipolar cells of the geniculate ganglion

 It also contains the efferent preganglionic parasympathetic fibers from the parasympathetic nuclei

two roots of the facial nerve emerge from the anterior surface of the brain between the pons and the medulla

They pass laterally in the posterior cranial fossa with the vestibulocochlear nerve and enter the internal acoustic meatus

On reaching the medial wall of the tympanic cavity, the nerve expands to form the sensory geniculate ganglion

 At the bottom of the meatus, the nerve enters the facial canal and runs laterally through the inner ear

descends behind the pyramid, and emerges from the stylomastoid foramen

Distribution

Facial nerve lesion

a lesion involving the upper motor neurons, only the muscles of the lower part of the face will be paralyzed

a lower motor neuron lesion—all the muscles on the affected side of the face will be paralyzed

Ramsay hunt syndrome

 Bell Palsy

is a dysfunction of the facial nerve, below the stylomastoid foramen; it is usually unilateral.

all the muscles on the affected side of the face will be paralyzed .

Loss of transverse wrinkle in the forehead

 lower eyelid will droop, and the angle of the mouth will sag.

Tears will flow over the lower eyelid, and saliva will dribble from the corner of the mouth

Food accumulate in the vestibule & dribble out between paralysed lip

The patient will be unable to close the eye and will be unable to expose the teeth fully on the affected side