Just the facial nerve (CN VII)

Question 1

Facial nerve pathway

Answer 1

Passes through the internal accoustic meatus and passes through the petrous portion of the temporal bone.

Question 2

What are the motor branches of the facial nerve?

Answer 2

• The posterior auricular branch to supply the occipitals and muscles that move the ear.
• the five terminal branches of facial expression
• The temporal branch; frontalis and obiqularis occuli muscles
• Zygomatic branch; supplies obiqularis occuli and zygomaticus major muscle
• the Buccal branch ; levator labiai m, the buccinator m, obiqularis oris m,
• Marginal mandibular branch; supplies depressor labiai inferioris, Depressor angli oris and mentalis m
• Cervical branch supplies the platysma muscles

Question 3

What are the 5 motor branches of facial nerve?

Answer 3

• Temporal
• Zygomatic
• Buccal
• Marginal mandibular
• cervical

Question 4

Whats the pathway of the greater superficial petrosal nerve and what is its function? (The first intracranial branch)

Answer 4

• It arises at the initial bend around the geniculate ganglion and contains presynaptic parasympathetic axons as well as a few taste fibers as well.
• it then re-enters middle cranial fossa through a small opening known as the hiatus of the facial canal; it runs antromedially inferiorly to the trigeminal ganglion
• The G. petrosal nerve dives into the foramenal serum containing the internal coratid artey and combines with the deep petrosal nerve which contains post ganglionic post sympathetic fibers branching from the superior cervical ganglion.
• The fused branch now contains both sympathetic and parasympathetic axons and courses through the pterygoid canal within the medial pterygoid plate to enter the pterygopalatine fossa

That is why this branch is known as the nerve to the pterygoid canal.

Question 5

What kind of neurons are found in the sphenopalatine ganglia?

Answer 5

Postsynaptic parasympathetic cell bodies stemming from the facial nerve.

Question 6

What happens every time we cry in terms of innervation?

Answer 6

=Preganglionic parasympathetic fibers originate from the superior salivatory nucleus in the brain stem; then course through the facial and greater petrosal nerve (through the pterygoid canal); Into the sphenopalatine ganglia where they synapse with postganglionic cell bodies then hop on the maxillary division of the trigeminal nerve and finally through the zygomatic nerve to the lacrimal nerve and then THE LACRIMAL GLAND.

Question 7

What is the pathway and function of the second intracranial branch the chordae tympani?

Answer 7

• Lateral branch of the facial nerve appearing right before the nerve exits through the stylomastoid foramen and it runs in a recurrent faction towards the middle ear. The nerve turns anteriorly between maleus and incus against the inner surface of the tympanic membrane.
• Though it is associated with the tympanic membrane physically (Right on it) it provides no innervation to it or any other structure in the middle ear.
• The chordae tympani then dives into petrotympanic fissure to emerge into the infratemporal fossa.
• in the depths of the infratemporal fossa, the chordae tympani emerges and infuses with the lingual nerve and travels to terminate in the submandibular ganglion as well as in the mucosa of the anterior 2/3 of the tongue.
• off the mucosa of the tongue, the chordae tympani brings special sensory information in the form of specialized chemo-receptors ( the fucking taste buds).
• The chemoreceptors then send the message back to the chordae tympani to be perceived as taste.

Question 8

What happens when we salivate?

Answer 8

• The superior salivatory nucleus in your brain stem sent a signal through parasympathetic through the facial nerves which jump off at the level of the chordae tympani; fuse with the lingual nerve and pass to the submandibular ganglion to synapse with postganglionic cell bodies these then project into the submandibular and lingual glands and increases saliva production.
• These glands also receive sympathetic innervation from fibers branching from the superior cervical ganglion and travelling with the lingual arteries.

Question 9

What is some nerve seven neuropathy (Bell’s Palsy)?

Answer 9

1/65 people will experience some sort of facial nerve neuropathy which is commonly referred to as bells palsy.

• The causes are still not very well understood even though it’s very prevalent.
• the condition is also more prevalent in diabetics and pregnant women which suggests there might be an endocrine or metabolic component.
• The condition may also be acute and temporary as it happens with an improperly placed nerve block for dental surgery.
• Since the facial nerve is responsible for facial expression then a damage to the nerve will result in inhibition of facial expression.

Question 10

What are the symptoms if the damage is external to the stylomastoid foramen?

Answer 10

-maybe due to mechanical trauma or parotid gland tumor; symptoms will be limited to a general motor.

Question 11

What are the symptoms are to the distal region of the facial canal?

Answer 11

• the chordae tympani might also be infected; in this case the patient might describe a change in taste perception and possibly dry mouth on the affected side.
• As well as possible motor dysfunction

Question 12

What if the damage is more proximal than the distal region of the facial canal?

Answer 12

• aside from the other motor and taste loss symptoms; the individual might also be sensitive to loud noises.
• This is due to a damage to the nerve to stapedius which causes the stapedius to contract to partially disarticulate the intrinsic bones within the middle ear to help buffer sound. without the activity of the stapedius muscle, the individual will be more susceptible to loud noises.
• As well as the damage from the more anterior portions.

Question 13

What if the damage is very proximal then what are more symptoms?

Answer 13

-the patient may experience eye irritation secondary to tear production to coat the anterior surface. The person will be prescribed an eye patch until symptoms resolved to stop drying out of the surface of the eye.

Question 14

If there is a damage anywhere in the facial nerve would there be problems with general sensation of the face? How is that important to differentiate between stroke or bells palsy?

Answer 14

No that is a function of the trigeminal nerve. This is important feature to differentiate Bell’s palsy from stroke which often presents with hemifacial paralysis
-Stroke would also be associated with some degree of paresthesia which is not seen with bells palsy.