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Old 04-26-2012
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Default Horner's ryndrome question

Guys, why there is a miosis in horner?

For example, if there is an aneurism or uncal herniation or apical lung tumor, whatever causes the III nerve palsy, I understand that there is a loss of CNIII function (which constricts the pupil) so there should be midrisas?

can someone explain?

Thank you.
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Default It's other way around

Sympathetic fibers through CNIII supply dilator pupillae via cervical symp ganglion which is damaged in Horneres >>>>there is unoppased action of sphincter pupillae leading to miosis.
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Miosis is because you can have an interruption of the superior cervical ganglion which is sympathetic.
-Source is page 413 FA 2011
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Horner's Syndrome is characterized by -

1) Miosis - pupil constriction
2) Ptosis - drooping of the eyelids
3) Anhidrosis - no sweating

Basically you can have a central lesion (in the descending hypothalamic pathway) or a peripheral lesion (in the superior cervical ganglion - via Sympathetic innervation; T1 to L2)

The sympathetics control the Radial Dilator muscle which contracts and causes mydriasis. If there is no Sympathetic innervation to that muscle (blockade OR a peripheral lesion in the sup. cervical ganglion) then that would lead to relaxation of the muscle leading to miosis.
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Miosis bcs of unopposed action of parasymp. System
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Quote:
Originally Posted by Sadde View Post
Miosis bcs of unopposed action of parasymp. System
In this case what will be unopposed?

The parasymp club is III, VII, IX, X.

CNIII is a constrictor.

The sympathetic system dilates the pupil.

So if there is a loss of parasymp contraction, it means that sympathetic system must take over and dilate.
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horners syndrome results from interruption of sympathetic supply to the eye
we know that the sympathetic nervous system is responsible for mydriasis(the radial muscle which has alpha 1 receptors)
miosis results because of the loss of this mydriasis( as it is under the control of sympathetic system)
the parasympathetic is left unapposed (parasym causes miosis thru the M receptors in sphincter pupillae)
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Default Correction

Quote:
Originally Posted by DocSikorski View Post
In this case what will be unopposed?

The parasymp club is III, VII, IX, X.

CNIII is a constrictor.

The sympathetic system dilates the pupil.

So if there is a loss of parasymp contraction, it means that sympathetic system must take over and dilate.
Symp fibers for sup cervical ganglion pass via > short cilliary nerve to reach dilator pupillae

sup cervical ganglion is damaged in Horners>>un-opposed parasympathetic activity parasympathetic innervation is via CNIII to sphicter pupillae>> miosis
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Nice! I am getting there!

Thank you guys!

Now its clear that there is a damage to sympathetic trunk and/or superior cervical ganglion which is a part of sympathetic pathway, affected are:
-dilator pupil mucle
-superior tarsal (Muller's) muscle of the eyelid.

=========

Here is another deal:
If parasympathetic pathway is taking over, I understand - there is miosis, cuz CNIII is a constrictor. But! CNIII is also elevates (!) the eylid through levator palpebrae
so why there is a ptosis then? (dropping of the eyelid)
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because superior tarsal muscle also help elevate the eyelid but its sympathetically innervated. so there is drooping of eyelid in horners
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Quote:
Originally Posted by pathophysio1 View Post
because superior tarsal muscle also help elevate the eyelid but its sympathetically innervated. so there is drooping of eyelid in horners
You need two opposite systems to elevate 1 eyelid? - doubtful!
What muscle drops the eyelid and how is it innervated?
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Quote:
Originally Posted by DocSikorski View Post
If parasympathetic pathway is taking over, I understand - there is miosis, cuz CNIII is a constrictor. But! CNIII is also elevates (!) the eylid through levator palpebrae
so why there is a ptosis then? (dropping of the eyelid)
Superior tarsal muscle, a part of levetor palpebrae is paralyzed in Horners leading to partial ptosis.. CNIII injury there will be complete ptosis along with Squint..
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Quote:
Originally Posted by Rookie View Post
Superior tarsal muscle, a part of levetor palpebrae is paralyzed in Horners leading to partial ptosis.. CNIII injury there will be complete ptosis along with Squint..
appreciate!
this is really helpful
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