Random Neuro facts

[Sir Elroy]

Fascinating idea. CNs I, II, and V are sensory, and CN II obviously responds to light, so it would be nice to be able to have CN II serve as a direct input to the photosnutatory reflex...but wouldn't the "motor" limb involve CN VII rather than CN V? CN V has has motor output, but this involve branchiomeric musculature. CN VII carries parasympathetic output that seems more involved in the reflex. The nasolacrimal discharge needn't be the "trigger" for the sneeze, though I think it is. It could just be an epiphenomenal component of this protective reflex.

I'm not aware of any proven link between CN II and CN V. And if there is, I don't see how the response (sneeze) would be any faster by virtue of having to go from CN II to CN V (and from thence presumably to CN VII) instead of following a different more direct path from V to VII.

Nick

My understanding of the theory (and granted, I think I'm basically over my head as a med student) is that a II-V or II-V-VII response would be faster than needing nasolacrimal discharge to tickle mucosa and trigger a sneeze, which may not fit with the speed observed.

I guess there's one thing I don't quite yet understand about a direct V-VII pathway: what exactly is causing the sneeze trigger, if not mucosal irritation? If the sneeze is just an epiphenomenon to the protective reflex, doesn't that make it a II-V-VII reflex, since II triggers the appropriate V nerve reactions to light?

I wish I had immediate access to the few journal articles on the reflex, but it seems I'll have to go to the library to read them. There is some theoretical discussion online, but most of it (like Wikipedia or the following link) just summarizes thoughts from the articles, and I've no way of knowing if that info is current.

http://loin.free.fr/john/medical_articles.html (Photic sneeze article list, information and some theoretical discussion)

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[neurodoc]

My understanding of the theory (and granted, I think I'm basically over my head as a med student) is that a II-V or II-V-VII response would be faster than needing nasolacrimal discharge to tickle mucosa and trigger a sneeze, which may not fit with the speed observed.

I guess there's one thing I don't quite yet understand about a direct V-VII pathway: what exactly is causing the sneeze trigger, if not mucosal irritation? If the sneeze is just an epiphenomenon to the protective reflex, doesn't that make it a II-V-VII reflex, since II triggers the appropriate V nerve reactions to light?http://loin.free.fr/john/medical_articles.html (Photic sneeze article list, information and some theoretical discussion)

It may be that the nasolacrimal discharge at "triggers" the sneeze, in which case it would be a II-V-VII reflex. I don't know for sure. It's certainly interesting.

 

[Sir Elroy]

It may be that the nasolacrimal discharge at "triggers" the sneeze, in which case it would be a II-V-VII reflex. I don't know for sure. It's certainly interesting.

Yup, it certainly is. I personally think it's great just to finally be able to put a name on and understand something I've done all my life. (I'm one of those weird sun-sneezers myself. I can get three or four sneezes with some bright lights, if I try.)