CRANIAL NERVE VII: FACIAL NERVE

Three Main Functions:

• Innervate the Muscles of Facial Expression
• Supply special sense of taste to anterior 2/3 of tongue, via Chorda Tympani Nerve.
• To innervate all facial glands (salivary, nasal, lacrimal), EXCEPT the Parotid.
• There is also a small area of somatic sensation carried by the facial nerve, around the ear canal ear drum.
• The GENICULATE GANGLION houses the cell bodies for all fibers of the Facial Nerve. It has no synapses.

PATHWAYS OF THE FACIAL NERVE:

1. Motor Fibers of Facial Expression (SVE):They all bend downward and all head out the Stylomastoid Foramen and then pass through the Parotid Gland (but they do not innervate it). Then they divide into five branches.
• All of these muscles are derived from the second branchial arch.
• TO ZANZIBAR BY MOTOR CAR:

1. TEMPORAL BRANCH -- Frontal Muscles

2. ZYGOMATIC BRANCH -- Orbicularis Oculi

3. BUCCAL BRANCH -- Buccinator, Orbicularis Oris, Zygomaticus

4. MANDIBULAR BRANCH -- Orbicularis Oris, Depressor Labii Inferiores

5. CERVICAL BRANCH – Platysma

2. Parasympathetic Secretomotor Fibers (GVE): They split into the Chorda Tympani and Greater Petrosal nerves, and head in two different directions.

1. PATHWAY OF CHORDA TYMPANI: Through Middle Ear ------> Out the Petrotympanic Fissure ------>Joins up with the Lingual Nerve ------> Submandibular Ganglion, where it synapses ------> Sublingual and Submandibular Salivary Glands

· So ultimate innervation is secretomotor innervation to Submandibular and Sublingual glands.

2. PATHWAY OF GREATER PETROSAL: Middle Ear ------> Out the Greater Petrosal Hiatus ------> back in through the foramen lacerum ------> Join with sympathetics from Deep Petrosal Nerve to form the Nerve of Pterygoid Canal ------> Pterygopalatine Ganglion, where it synapses ------> Nasal mucosa and Lacrimal Glands.

· So, ultimate innervation is secretomotor innervation to lacrimal glands and nasal mucosa.

BELL'S PALSY: "Paralysis of the Facial Nerve for no obvious reason." Or, loss of SVE motor innervation of the Facial Nerve.

• Commonly occurs if the nerve gets impeded or inflamed at the Stylomastoid Foramen.
• Facial paralysis results on the side affected. Patients will be unable to close eyelids, they will drool, and they will have a contorted face due to unopposed muscles on other side.
• An injury here would not affect parasympathetic secretomotor innervation (those are given off before the Stylomastoid foramen) -- it would only affect muscles of facial expression.
• Loss of buccinator muscle can lead to difficulty eating.
• Inability to close eyelid results in damage to cornea due to dryness of the eye, due to no innervation of palpebral part of orbicularis oculi.
  

Category: Anatomy Notes