YogaGYE
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25. A normal brain is shown. An 80% loss of neurons in the structure labaled X will create a state of disinhibition in wich of the following areas of the brain?
A) Basal forebrain
B) Dentate nucleus
C) Hippocampus
D) Hypothalamus
E) Striatum
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| alb123
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thats hard.. cant figure out where the substantia nigra causes inhibition that would yeild to disinhibition when injured, im assuming the symptoms would be parkonsin-like. I would guess E the striatum because it has dopamine receptors, but i could use some help.
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| sanmatt
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I agree with alb123
Striatum is correct answer. The picture shown is midbrain and pointer is on substantia niagra. The dopamine fibers from substantia niagra project to striatum (Ach neurotransmiter) which consist of D1 and D2 receptors. At D1 receprots (which is direct pathway to thalamus)the dopamine fibers are inhibitory therefore reduced amount of fibers will couse disinhibition at D1 receptor. At D2 receptor(which is indirect pathway to thalamus trough subthalamic nuclei) the dopamine fibers are activating.
hopes it helps
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| Diego Casali
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I agree.
E is the correct answer.
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| Dr.Papez
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This question was discussed twice here. You may find these links useful.
http://www.prep4usmle.com/forum/thread/38533
http://www.prep4usmle.com/forum/comments.php?id=3...
Bye
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| quansar
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No, hypothalamus is the answer.
Dopamine (via D1) activates the Striatum, which will dishibit GP and consequencly disinhibit thalamus for an activating effect.
D1's direct effect on striatum is excitory therefore losing neurons in substantia nigra will be loss inhibition to stiatum, which will not inhibit globius, and then glob's inhitory effect on thalamus dominates, the outcome is lack of motion.
my two cents
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| quansar
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sanmatt, for your info, D1 receptor is coupled to increases in cAMP and is typically excitatory
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| quansar
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sorry, typo
D1's direct effect on striatum is excitory therefore losing neurons in substantia nigra will be loss excitation to stiatum,
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| Revenged
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Ok, I'll put things together a bit...
Parkinson's - Loss of dopamine neurones from substantia niagra to the striatum
This loss of dopamine neurones to the striatum cause increased activation of acetylcholine neurones in the striatum...
This increase in activation of acetylcholine neurones leads to resting tremor you see in parkinson's patients...
Why is this important?
Because you can give a muscarinic antagonist (e.g. atropine) to decrease the activation of acetylcholine neurones from the striatum, which reduces the resting tremour you have in parkinson's...
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