Question about the ear

[Phloston]

Does anybody know which nerve innervates sensation to the auditory canal just external to the tympanic membrane / tympanic membrane itself?

Is it just the ophthalmic branch of the trigeminal? I had the impression that this may have been an exception and that it could be the facial nerve instead (considering deep ear cleaning can induce lacrimation). I've also read that pre-auricular pain is facial nerve-mediated (USMLE Rx liked that), not trigeminal-, so I'm curious if someone could briefly elaborate here.

Cheers,

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[lrkoehle]

Not sure if this is going to be the level of detail that you're looking for, but I'll try my best based on what I have seen in Kaplan and UW qbanks. To start, most of the ear is innervated by the mandibular division of the trigeminal nerve (V3). This supplies the anterior half of the external auditory canal; however, the posterior half of the auditory canal is the auricular branch of the vagus nerve. On top of that, the inner surface of the tympanic membrane is apparently taken care of by the glossopharyngeal nerve. A fun fact is that apparently the vagal innervated portion can lead to a vasovagal response in some people when stimulated, there by leading to bradycardia and hypotension...anyways, that's basically all I have in my notes about the auditory canal sensory innervation.

 

[JackShephard MD]

Not sure if this is going to be the level of detail that you're looking for, but I'll try my best based on what I have seen in Kaplan and UW qbanks. To start, most of the ear is innervated by the mandibular division of the trigeminal nerve (V3). This supplies the anterior half of the external auditory canal; however, the posterior half of the auditory canal is the auricular branch of the vagus nerve. On top of that, the inner surface of the tympanic membrane is apparently taken care of by the glossopharyngeal nerve. A fun fact is that apparently the vagal innervated portion can lead to a vasovagal response in some people when stimulated, there by leading to bradycardia and hypotension...anyways, that's basically all I have in my notes about the auditory canal sensory innervation.

I was typing out a vagus nerve response but you beat me to it.

 

[loveoforganic]

Additionally, that's why you can get a cough reflex there (arnold's reflex)

I think vagus is the afferent for the vomit reflex you can get there as well

 

[Phloston]

So the outer ~1/2 of the auditory canal is V3, not V1. What about the pinna / external structures then?

If the tympanic membrane has sensation innervated by the glossopharyngeal, and the posterior/inner portion of the canal is Vagus, is the facial nerve not involved at all?

Thanks for the replies btw.

 

[loveoforganic]

I seem to remember the facial having a branch somewhere in there as well. I feel like I remembered it as a weird triad. Never memorized the areas of innervation though

 

[Phloston]

I think part of my own question just clicked for me. If V3 does the outer 1/2 of the auditory canal, considering the corneal reflex / orbital irritation can produce lacrimation (V1-VII), that would explain the V3-VII afferent-efferent there.

However I'd still like to know if facial plays a role in sensation regarding the ear.

 

[loveoforganic]

Doesn't answer your question, but GT says mixed innervation between X and V3 for the external half of the tympanic membrane

 

[liability]

Anterior half of external canal - auriculotemporal V3
Posterior half of external canal - auricular br of vagus
Upper half of auricle C2 lesser occipital
Lower half of auricle C2-3 greater auricular

 

[Phloston]

Doesn't answer your question, but GT says mixed innervation between X and V3 for the external half of the tympanic membrane

Anterior half of external canal - auriculotemporal V3
Posterior half of external canal - auricular br of vagus
Upper half of auricle C2 lesser occipital
Lower half of auricle C2-3 greater auricular

Awesome, cheers,

If anyone else has any info, that would be great.

 

[tjquinn]

Well, the external and middle ear are derived from branchial arch 1 and pouch 1, so the main innervations are going to be via trigeminal, BUT! my favorite muscle in the body is in the ear and is innervated by VII.

Our friend the stapes (smallest bone in the body) plays a role in conducting sound and if suddenly a loud noise caused the stapes to oscillate to rapidly, the result would be pain. So, because the stapes is branchial arch 2, CN VII will innervate the muscle that dampens stapedial oscillation via the stapedius. In a way, CN VII is "sensing" the movement of the stapes to prevent it from shaking too violently.

Why is this the coolest muscle? Did you ever notice that when you speak, you hear your own voice in a particular way, and if you listen to yourself on recording, or watch a video of yourself, the voice sounds somewhat different, perhaps annoying (since you already have an expectation of the voice)? Well, I can't stand hearing my own voice (for instance on recordings, movies, etc.) and my stapedius alters the way that I hear my voice when I speak to prevent it from being overwhelmingly loud, but this also modifies the quality of my own perception of my voice (which is fine with me).

 

[Phloston]

Well, the external and middle ear are derived from branchial arch 1 and pouch 1, so the main innervations are going to be via trigeminal, BUT! my favorite muscle in the body is in the ear and is innervated by VII.

Tjquinn, branchial arch 1 forms the middle ear, but did you mean cleft, not pouch, for the external ear? Pouches are endodermal.

Our friend the stapes (smallest bone in the body) plays a role in conducting sound and if suddenly a loud noise caused the stapes to oscillate to rapidly, the result would be pain. So, because the stapes is branchial arch 2, CN VII will innervate the muscle that dampens stapedial oscillation via the stapedius. In a way, CN VII is "sensing" the movement of the stapes to prevent it from shaking too violently.

The USMLE apparently likes that tid bit. I've encountered questions where they describe someone with loss of facial muscle function (implying CNVII deficit), then they ask about another possible Sx, and ipsilateral hyperacusis is what they shoot for, based on lack of stapedius function.

 

[VisionaryTics]

1st cleft -> External ear
1st & 2nd pouch -> Middle Ear / pharyngotympanic tube

VII innervates stapedius, V3 innervates tensor tympani. Both decrease the gain across the ossicles.

VII also has GSAs of embryologic importance on the external auricle and external surface of TM.

 

[tjquinn]

Tjquinn, branchial arch 1 forms the middle ear, but did you mean cleft, not pouch, for the external ear? Pouches are endodermal.

Whoops, I meant branchial cleft (or groove) forms external ear, branchial arch forms bones of the middle ear and branchial pouch forms the middle ear cavity.

 

[futuredoctor10]

Yep there is a UWorld question about hyperacusis & stapedius!

It's interesting some of the things UW (& presumably Step 1) finds important...

 

[Phloston]

Yep there is a UWorld question about hyperacusis & stapedius!

It's interesting some of the things UW (& presumably Step 1) finds important...

Honestly, futuredoc, it's not even about what's important. It's just that when you do enough questions, there aren't any surprises anymore. That should be a lesson learned for all of us.

 

[loveoforganic]

Yep there is a UWorld question about hyperacusis & stapedius!

It's interesting some of the things UW (& presumably Step 1) finds important...

On that note, based on stapedius lesion = hyperacusis and tensor tympani lesion = hypoacusis, I've made the assumption (but haven't read anywhere) that tensor tympani, in addition to being responsible for attenuating noise intensity, is also responsible for some kind of tonic contraction of the tympanic membrane to allow sound conduction altogether.

Is this actually the case? If not, can someone explain the hypoacusis?

 

[DeadByDawn]

On that note, based on stapedius lesion = hyperacusis and tensor tympani lesion = hypoacusis, I've made the assumption (but haven't read anywhere) that tensor tympani, in addition to being responsible for attenuating noise intensity, is also responsible for some kind of tonic contraction of the tympanic membrane to allow sound conduction altogether.

Is this actually the case? If not, can someone explain the hypoacusis?

I'd like to know this as well. does anyone have an answer???

 

[GTP]

According to gt the inner tympanic membrane/tympanic cavity are supplied by IX. I didn't see that mentioned here yet.

 

[medstudentASY]

Why is this the coolest muscle? Did you ever notice that when you speak, you hear your own voice in a particular way, and if you listen to yourself on recording, or watch a video of yourself, the voice sounds somewhat different, perhaps annoying (since you already have an expectation of the voice)? Well, I can't stand hearing my own voice (for instance on recordings, movies, etc.) and my stapedius alters the way that I hear my voice when I speak to prevent it from being overwhelmingly loud, but this also modifies the quality of my own perception of my voice (which is fine with me).

That is pretty neat. Thanks for this fun fact!

 

[happyfeet123]

FA doesnt have any ear anatomy.but i've heard people get ear questions. Any advice for review stuff on the ear before I take this badboy on Monday? Thanks

 

[Phloston]

FA doesnt have any ear anatomy.but i've heard people get ear questions. Any advice for review stuff on the ear before I take this badboy on Monday? Thanks

BRS Physiology has a little bit in there on the ear.

I think it's a bit odd that FA2012 doesn't have this stuff. I also own the 2009 edition, and there's a full page on it. Why they removed it is beyond my comprehension.