Q.9
The facial nerve :
A. Arises from the Medulla
B. Traverses through parotid Gland
C. Supplies Muscles of Mastication
D. Caries no taste Fibers
Explanation :
Anatomically, the course of the facial nerve can be divided into two parts:
- Intracranial – the course of the nerve through the cranial cavity, and the cranium itself.
- Extracranial – the course of the nerve outside the cranium, through the face and neck.
Intracranial
The nerve arises in the pons, an area of the brainstem. It begins as two roots; a large motor root, and a small sensory root (the part of the facial nerve that arises from the sensory root is sometimes known as the intermediate nerve).
Still within the temporal bone, the roots leave the internal acoustic meatus, and enter into the facial canal. The canal is a ‘Z’ shaped structure. Within the facial canal, three important events occur:
- Firstly the two roots fuse to form the facial nerve.
- Next, the nerve forms the geniculate ganglion (a ganglion is a collection of nerve cell bodies).
- Lastly, the nerve gives rise to:
- Greater petrosal nerve – parasympathetic fibres to mucous glands and lacrimal gland.
- Nerve to stapedius – motor fibres to stapedius muscle of the middle ear.
- Chorda tympani – special sensory fibres to the anterior 2/3 tongue and parasympathetic fibres to the submandibular and sublingual glands.
The facial nerve then exits the facial canal (and the cranium) via the stylomastoid foramen. This is an exit located just posterior to the styloid process of the temporal bone.
Extracranial
After exiting the skull, the facial nerve turns superiorly to run just anterior to the outer ear.
The first extracranial branch to arise is the posterior auricular nerve.
It provides motor innervation to the some of the muscles around the
ear. Immediately distal to this, motor branches are sent to the
posterior belly of the digastric muscle and to the stylohyoid muscle.
The main trunk of the nerve, now termed the motor root of the facial nerve, continues anteriorly and inferiorly into the parotid gland .
Within the parotid gland, the nerve terminates by splitting into five branches:
- Temporal branch
- Zygomatic branch
- Buccal branch
- Marginal mandibular branch
- Cervical branch
These branches are responsible for innervating the muscles of facial expression
