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YuQX
06-19-2006, 12:05 PM
When you isolate and sever glossopharyngeal afferent fibers which supply the carotid sinus, the firing rate of carotid sinus increases or decreases? You will see bradycardia or tachycardia?

md90
06-19-2006, 12:44 PM
When you isolate and sever glossopharyngeal afferent fibers which supply the carotid sinus, the firing rate of carotid sinus increases or decreases? You will see bradycardia or tachycardia?

first, what happens to the carotid sinus normally r/t baroreceptors? Baroreceptors normally sense via stretch of the arterial wall..and sends it to the medulla; for example: hypotension.. less stretch leading to decreased afferent firing...increased stimulation of parasympathetic and sympathetic activity leading to increased HR and BP, vasoconstriction, and increased contractility.

Therefore if that connection from the afferent fibers is "lost", then there is nothing telling the brain that the stretch has decreased, and to decrease the afferent fibers firing rate (increase the rate); will see bradycardia...

But then we have the chemoreceptors that sense changes in relation to the pH, PO2, PCO2..

Please correct, add, comment,..... thank you for the question :p

Billy BA
06-19-2006, 11:16 PM
I think that md90 is off on his explanation by a good bit. Decreased barorecptor activity at the carotid sinus will feedback to the medulla and lead to decreased parasympathetic activity and increased sympathetic activity.

When you sever Hering's nerve (CN IX from the sinus) then there will be no afferent activity transmitted to the CNS leading to increased heart rate, increased TPR, and all the other systemic sympathetic responses b/c the brain is translating this lack of afferent signals as 0 Mean Arterial Pressure.

md90
06-20-2006, 12:15 AM
thank you Billy BA... I'm an IDIOT... totally forgot about the sympathetic effects...

Billy BA
06-20-2006, 05:23 PM
No problem md90, it's easy to overlook even the simpliest of things. I only posted a reply b/c I didn't want people to think the wrong thing when studying for Step 1.

md90
06-20-2006, 09:53 PM
I greatly appreciate that... I would have felt bad if someone made a mistake b/c of what I did or did not tell them... thank you for "watching my back.." :)

YuQX
06-20-2006, 11:34 PM
After I did a very silly mistake on that Qbank question, now I figured out this baroreceptor reflex.
Sever CN IX afferent fibre which supplies carotid sinus------firing rate of carotid sinus decreases------parasympathatic nerve activity decreases and sympathetic nerve activity increases-----tacycardia, hypertension, etc.
Stimulate carotid sinus-------firing rate of carotid sinus increases----parasympathetic nerve activity increases----bradycardia, hypotension, etc.
Baroreceptor on aortic arch is supplied by CN X.

navpreet
06-21-2006, 09:28 AM
:D i really appreciate the effort of u guys, trying to help us all,preparing for step 1.
thanks.

lovetiesto
09-05-2006, 12:45 PM
another easier way to interpret baroreceptor reflex atleast for myself...

Increased Afferent activity(volume load, carotid message, wieghtlessness) => Increased Parasymp. at same time Decrease Symp=> Dec B.P.=> Dec H.R. (Also, another easier way think that if afferent activity increases brain will interpret it as State of hypertesion, so it will inc para stimulation, dec symp, dec H.R., Dec B.P.)


Like wise Decrease afferent activity => dec para at same time increase sympathetic=> inc B.P.=> inc H.R.

Remember afferent activity and parasyp changes in same direction and (sympthetic activity, HR, BP, changes in same direction). this is true in all baroreceptor refelexes.

So, cutting nerve IX(or lying to stand, fluid loss, carotid occulusion) will decrease afferent activity(brain interpretation state of Hypotension)=>dec para and inc symp=> inc H.R..=> inc B.P..


i hope this helps somehow.....







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