Block II: facial nerve

Question 1

the facial nerve comes form? and arises from?

Answer 1

Nerve of the 2nd branchial arch

Arises from the brainstem as two branches:
*branchial motor
*sensory and parasympathetic
(nervus intermedius)

Question 2

explain the trajectory of facial nerve

Answer 2

as ir emerges from the brainstem it enters the internal acoustic meatus and in the petrous portion of temporal bone and then it has the genu and continues in the facial canal and emerges through the stlomastoid foramen

Question 3

which are the components of the Facial nerve and its innervations?

Answer 3

A. Branchial Motor (SVE)
Stapedius, Stylohyoid,
Posterior belly of Digastric,
Muscles of Facial Expression

B. Visceral Motor (GVE)
Lacrimal gland, Submandibular
and Sublingual glands, Mucosal
glands of nose and palate

C. General Sensory (GSA)
Skin of concha of auricle,
small area of skin behind ear,
wall of external acoustic
meatus and external tympanic
membrane

D. Special Sensory (SVA)
Taste from anterior 2/3 of
tongue, and hard and soft
palates

Question 3

where is upper motor neuron and lower motor neuron located (facial nerve) and its terminal branches of the branchial motor component (SVE)

Answer 3

UMN - Motor cortex
LMN - Motor nucleus of CN VII (within pons)

Terminal branches:
N. to stapedius
Posterior Auricular N.
N. to stylohyoid
N. to posterior bellyof digastric
Branches to musclesof facial expression

Question 4

Explain the axon distribution of the upper and lowr motor neurons nuclei of CN VII and how do muscles innervate?

Answer 4

Motor neurons from the cortex send axons to both motor nuclei of CN VII (bilateral input). Neurons in the dorsal half of these nuclei receive input from both sides of the cortex, while those in the ventral half receive input from only the opposite side (contralateral input

Muscles in the upper half of the face are innervated by upper neurons that receive bilateral input from dorsal part of nuclei. Muscles in the lower half of the face are innervated by lower motor neuron that receive contralateral input from ventral part of nuclei only.

This is relevant when interpreting symptoms due to lesions associated with CN VII.

Question 5

explainn the geenral senspry comppnent of the facial nerve general somatic afferent

Answer 5

Cell body of afferent fibers found in the Geniculate Ganglion

Dendrites bring information through nervus intermedius, from:
*skin posterior to ear
*skin of concha of auricle
*wall of external acoustic meatus
*external tympanic membrane

Axons will synapse with neurons in the spinal nucleus of CN V within the brainstem