EKBio1001 Nervous system questions

[basophilic]

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Question 277: you absorb a toxin that blocks acetylcholine; what's the consequence?
B) CNS neuronal degenration and death
C) respiratory muscle paralysis
D) rapid heart rate and dehydration

C doesn't make sense because lungs can still respond to SNS hormones like epinephrine
B makes sense because lack of neuronal transmission WILL cause neurons to feel useless and die
D makes MOST sense because lack of stimulation from vagus nerve should allow heart to be in default state of 100+ beats/min

Question 412: What must be true about muscle cell with following properties?
Resting potential = -90 mV
depolarization ion = Na
AP duration = 5 ms
thin filament = actin G
AP spread = T-tubules

Answer choices with my reasoning:
B) the cell is hyperpolarized at -110 mV --> saw this is incorrect b/c question says "must be" and the cell NEED not have -110, but it MUST BE something less than -90
C) it's a voluntary controlled cell --> saw this as correct because depolarization ion is only Na, and everything else fits criteria of skeletal muscle
D) it's a cardiac muscle cel --> saw this as incorrect b/c I remember cardiomyocytes depolarization involves Ca as well as Na

 

[sc4s2cg]

Hi, can you post the official answers too please?

Edit: and also what you are confused about as well.

 

[basophilic]

Hi, can you post the official answers too please?

Edit: and also what you are confused about as well.

Oops my bad.
Answers in the book are C for 277 and B for 412. I described my reasoning above for D (for 277) and C (for 412). Thanks.

 

[sc4s2cg]

277:

B) so this is talking specifically about the CNS, and you may remember that Ach is usually emitted by either interneurons or the parasympathetic nervous system. Ach is not limited to only the CNS as the Peripheral NS also has it. This answer is too specific. Furthermore, neurons will degenerate and die because of lack of stimulation, which can be provided through Ne/E.

C) in this case the lungs are no longer effected by the parasympathetic NS, so like you said they will have Ne/E stimulation. Ne/E is released by Sympathetic, so the lungs are constantly stimulated to increase respiration. Eventually this causes paralysis.

D) Actually I'm not clear on why D is wrong here. I think I remember that only the vagus nerve goes to the heart parasympathetic-wise, but I will get back to you after some research. Do the answers say anything?

412:

B) I would pick B purely on elimination, but I'm not sure why they are implying that the cell must be hyperpolarized at -110. Is there any reasoning in the answers?

C) You are correct that everything leads to skeletal muscle, but also remember that there is some skeletal muscle that is involuntary. Like. Furthermore, T-Tubules exist in cardiac and smooth muscle as well.

D) Yes, you are correct in this reasoning.

 

[basophilic]

277:

B) so this is talking specifically about the CNS, and you may remember that Ach is usually emitted by either interneurons or the parasympathetic nervous system. Ach is not limited to only the CNS as the Peripheral NS also has it. This answer is too specific. Furthermore, neurons will degenerate and die because of lack of stimulation, which can be provided through Ne/E.

C) in this case lungs are no longer effected by the parasympathetic NS, so like you said they will have Ne/E stimulation. Ne/E is released by Sympathetic, so the lungs are constantly stimulated to expand. This causes paralysis.

D) The heart is interesting in that it receives

Sent from my SCH-I545 using Tapatalk

C) epinephrine stimulation would increase respiratory rate, not only lung expansion, so how can that paralyze the lung? as far as i know epinephrine only affects the smooth muscle in lung which is around the bronchi/bronchioles - increased epinephrine would just cause bronchodilation

 

[sc4s2cg]

I updated my post, had to switch from mobile to PC.

Regarding C: I'm not sure of the details, but this is something that's been hammered in my head throughout undergrad. I'll get back to you on this one.

 

[amy_k]

http://forums.studentdoctor.net/threads/nervous-system-question-ek-bio-1001-277.753636/

 

[amy_k]

I think this is the original question for 277

 

[amy_k]

My opinion is that C is the BEST answer since respiratory paralysis leads to death before dehydration occurs. There would likely be respiratory paralysis and rapid heart rate and death shortly after unless the toxin effects were reversed. Rapid heart rate and dehydration seem less significant than C.

 

[amy_k]

@sc4s2cg and here is the full q for #412 http://forums.studentdoctor.net/threads/ek-1001-biology-answer-error.395478/

 

[amy_k]

I think OP's reasoning for answer C in #412 is correct and the thread i posted regarding the same question came to the same conclusion. This is most likely a skeletal muscle, but that the cell is hyperpolarized at -110mV is the more obvious answer.

 

[amy_k]

C doesn't make sense because lungs can still respond to SNS hormones like epinephrine

specifically responding to this comment from OP, Ach and Ep work antagonistically on smooth respiratory muscle, if Ach is blocked then smooth respiratory muscles cannot contract, therefore the relax response is useless and suffocation still occurs.

 

[basophilic]

http://forums.studentdoctor.net/threads/nervous-system-question-ek-bio-1001-277.753636/

Oops, I should have done my research of past threads before asking here. Thanks for posting the links.
But to your last response, I agree that lack of Ach can prevent bronchial muscle from constricting; but presence of primarily epinephrine can't cause "constriction" - if anything, bronchodilation should facilitate breathing; also you'll breathe faster

 

[amy_k]

I am imagining that the diaphragm is also paralyzed, so this is fundamentally preventing the person from taking in any air even if the broncho passages were dilated due to ep.

 

[amy_k]

Anyway, this kind of toxin is a real life situation (google botulinum toxin) which is known to pose the threat of death by suffocation due to flaccid paralysis as a result of blocking ach and the effects of this reaching respiratory muscle. So this question is correct.

 

[amy_k]

https://books.google.co.uk/books?id...laccid paralysis botulism suffocation&f=false

Not sure if you can see this link.

 

[RH8448]

I just have some dissonance with some of these answers.

For the first one it is respiratory paralysis. We need to contract our diaphragm and intercostals to allow air to fill our lungs. These skeletal muscles are acted on by Acetlycholine. I'm not sure what the background is about but epinephrine doesn't seem to be involved. D is correct, because once the vagus nerve is "cut" heart rate spikes because the vagus nerve slows down the heart rate by maybe 25beats/min. I'm not sure about dehydration so I choose B.

For the second one: Na+ doesn't depolarize muscle cells. Na+ depolarizes neurons and releases Acetlycholine at the synapse. That neurotransmitter causes Ca2+ to depolarize the myocyte. I reasoned that what must be true is that all myocytes must be polarized (in order to be depolarized and useful). My concern for this question would be whether all muscle cells have T tubules and actin which I think they do. The length of the action potential can vary between different types of muscle cells (heart, skeletal). Does this make sense or am I missing something?

 

[ChrisMack390]

I think a lot of you are overthinking these questions.

The first one is C because when you read that question you should instantly be thinking "ok, no acetycholine, there is going to be some kind of muscle paralysis" and then only choice C has anything to do with that.


For the second one, if that cell is at -110, it MUST BE hyperpolarized, because it isn't supposed to be at -110, it is supposed to be at -90. Sure, if it was at -108 or -115 or -92 it would also be hyperpolarized, but no where did they say that -110 was the only possible value at which it is hyperpolarized, they just say that if the cell IS at -110, then it IS hyperpolarized.

Remember the MCAT is usually not testing specialized minutia, they are frequently just testing your critical thinking and process of elimination.