Two questions on muscle

[AZFutureDoc]

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Hey guys, I have two questions in EK biology, page 165.

Number 182: Cardiac is excited by:
A: Parasympathetic nervous excitation.
B: Constriction of T-tubules.
C: Increased cutosolic sodium concentration.
D: Increased cytosolic calcium concentration.

My answer was D. Sodium slowly leaks into muscle cells to cause a contraction. Their answer is C. Why is C any better than D? Is this just a dumb question, or is D really not true?

Next, 184: In the cold, just before frostbite, sudden vasodilation occurs manifesting in flush skin. This vasodilation is most likely the result of:
A: paralysis of smooth muscle in the vascular walls
B: paralysis of skeletal yscle surrounding the skeletal walls
C: sudden tachycardia with a resultant increase in blood pressure
D: blood shunting due to smooth muscle sphincters.

I put D, even though I wasn't sure. I felt I was able to eliminate A, which they say is correct. Cold weather paralyzing smooth muscle? Seemed like BS. Is this true? D just seemed perfect, I was just unsure about the sphincter part.

Thanks guys.

 

[spyderracing32]

Well assuming 182 is in reference to neuron input then it is the influx of sodium into the muscle fiber that triggers depolarization of the sarcolemma and consequently the sarcoplasmic reticulum (which subsequently releases Ca2+ into the sarcoplasm allowing for contraction).

For 184, D is going to be incorrect because in cold temperature your body is going to try to conserve your core body temperature, so blood is shunted away from the skin and the extremities; this is why your toes and fingers are the first to succumb to frost-bite. In terms of homeostasis, blood is shunted to the surface in order to radiate heat (flushing). Both are mechanisms to maintain your core temperature, but neither are facilitated by smooth muscle sphincters (present in veins to prevent gravitational back flow; a common cardiopathy in diabetes is the loss of function of these sphincters resulting in edema aka "diabetic foot"), rather they occur by constriction and dilation of the vessels themselves.

B and C are just ridiculous choices, and A is correct. Think about if you've ever had to do anything in the cold. How well do you hands and other skeletal muscles work? The same mechanism is at play in smooth muscle save the fact that troponin/tropmyosin are replaced by calmodulin. Since the smooth muscle is contracted to constrict surface blood vessels in order to maintain core body temperature, the only result of paralysis of these muscles can be dilation of the blood vessels subsequently increasing blood flow to the surface and resulting in flush skin.

 

[AZFutureDoc]

This may be really dumb, but I was thinking flush meant pale. I now realize it means red. So ya, this makes sense. My vocab managed to completely turn the question around 180 degrees. Thanks.

 

[Vihsadas]

Just to add to spyder's explanation (which is right), I think your problem with number one was that you confused the meanings of 'excite' and 'contract'. It's an easy mistake to make.

Sodium from a neural AP is exciting the muscle cell, and then calcium is released causing the contraction.

 

[jisu23]

The answer in my EK book is D for #182..

 

[TieuBachHo]

I understand what Spiderracing32 is saying but how exactly smooth muscle paralysis lead to vasodilation? If paralysis consequences in stretching of smooth muscle then it's not vasodilation because smooth muscle still functions properly with vasodilation, or is it? And most importantly how exactly cold weather causes smooth muscle paralysis? Is there somehow a miscommunication of smooth muscle with PNS in a way? Man this question makes me mad LOL 😀

It makes sense to me if the smooth muscle paralysis is a pre-condition that leads to the skin flush and not a consequence of cold weather?

I can't find any reliable source that explains this phenomena. Any help is much appreciated!!! 😕😕😕