Epinepherine, EK Exam 4, Passage 1 (7th edition)

[theyellowking]

I have two questions that I am still confused about after reading the answer and explanation to both. I will copy/paste both the questions and answers:

Q72: Which of the following cell types most likely contain adrenergic receptors (receptors that respond to epinephrine)?:
A. chromaffin cells
B. sympathetic postganglionic neurons
C. parasympathetic postganglionic neurons
D. cardiac muscle cells

In my head, I immediately associated epinephrine with sympathetic, thus eliminating C, and choosing B. However, the answer was as follows:
AtoQ72: Cardiac cells are innervated by both autonomic nervous systems. Sympathetic neurons release epinephrine onto cardiac muscle cells. A and B would be expected to have similar receptors because chromaffin cells are modified postganglionic sympathetic neurons. All autonomic preganglionic neurons release acetylcholine onto postganglionic neurons.

Although I learned that cardiac cells are innervated by both sympathetic and parasympathetic, it seemed to me that the question simply asked for which responds to epinephrine?

Q76: Amphetamines cause epinephrine to be released from the ends of associated neurons. Which of the following is most likely NOT a symptom of amphetamine usage?
A. increased heart rate
B. elevated blood glucose
C. constricted pupils
D. increased basal metabolism

Although I chose choice C since it contrasted with the information I read earlier, I was still confused about choice D. Since sympathetic is associated with "flight or flight," thus decrease digestive activity, shouldn't D. not be associated with sympathetic? The answer gave no explanation of why you should not pick D.

Biology is one of my weakest, and since I had to learn this subject from EK for the first time, I've had a lot of difficulty handling the subject. Do you guys recommend any useful specific videos/websites to use?

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[sillyjoe]

I have two questions that I am still confused about after reading the answer and explanation to both. I will copy/paste both the questions and answers:

Q72: Which of the following cell types most likely contain adrenergic receptors (receptors that respond to epinephrine)?:
A. chromaffin cells
B. sympathetic postganglionic neurons
C. parasympathetic postganglionic neurons
D. cardiac muscle cells

In my head, I immediately associated epinephrine with sympathetic, thus eliminating C, and choosing B. However, the answer was as follows:
AtoQ72: Cardiac cells are innervated by both autonomic nervous systems. Sympathetic neurons release epinephrine onto cardiac muscle cells. A and B would be expected to have similar receptors because chromaffin cells are modified postganglionic sympathetic neurons. All autonomic preganglionic neurons release acetylcholine onto postganglionic neurons.

Although I learned that cardiac cells are innervated by both sympathetic and parasympathetic, it seemed to me that the question simply asked for which responds to epinephrine?

Q76: Amphetamines cause epinephrine to be released from the ends of associated neurons. Which of the following is most likely NOT a symptom of amphetamine usage?
A. increased heart rate
B. elevated blood glucose
C. constricted pupils
D. increased basal metabolism

Although I chose choice C since it contrasted with the information I read earlier, I was still confused about choice D. Since sympathetic is associated with "flight or flight," thus decrease digestive activity, shouldn't D. not be associated with sympathetic? The answer gave no explanation of why you should not pick D.

Biology is one of my weakest, and since I had to learn this subject from EK for the first time, I've had a lot of difficulty handling the subject. Do you guys recommend any useful specific videos/websites to use?

Let's start with question 72 which is essentially asking which of the following cell types respond to sympathetic stimulation and go answer by answer. Chromaffin cells which are located in the adrenal gland are just modified sympathetic post-ganglionic cells that release epinephrine/norepinephrine into the blood stream as a hormone as opposed to releasing it as a neurotransmitter into the synaptic junction. Now you should know that all autonomic pre-ganglionic fibers whether they are sympathetic or parasympathetic releases acetycholine into the synaptic junction which binds to a receptor (nicotinic cholinergic) on the POST-synaptic cell. Therefore, any post-synaptic neuron should NOT have a membrane receptor for epinephrine/norepinephrine (adrenergic) since the pre-ganglionic nerve fibers will ONLY release acetylcholine so it would be pointless to have an adrenergic receptor there. Since choices A, B, and C are all post-ganglionic fibers/nerves (or modified post-ganglionic fibers), they should only have cholinergic receptors, and thereby the ability to respond to acetylcholine.

Now some post-ganglionic fibers will release epinephrine. Therefore, a TARGET of a post-ganglionic fiber should have adrenergic receptors (ones that respond to epinephrine/norepinephrine). Cardiac cells fit the description of a target cell for a post-ganglionic fiber, specifically a sympathetic post-ganglionic fiber and therefore should have an adrenergic receptor.

Question 76 is essentially asking, "Which of these choices is not a sympathetic response?". We know that choice A is obviously a sympathetic response so we can cross that out immediately. We also know, that if I need to run away from a tiger that wants to eat me, I better have elevated blood glucose to supply my muscles. I also better have increased basal metabolism to supply enough ATP (energy) for me to run away from said tiger. So we could have used process of elimination to get to answer choice C. Now if you really wanted to know the science behind it, the sympathetic nervous system is used to dilate the pupils and the parasympathetic nervous system is used to constrict the pupils. If you want an easy way to remember that just think of night time hunting and survival (sympathetic responses) thousands of years ago. In order to hunt at night or not be eaten by that dingus tiger we must be able to SEE well and dilating our eyes would do that and is therefore a sympathetic response.

 

[theyellowking]

Ah, amazing explanation. Thank you so much

 

[theyellowking]

And I'm not sure if this is too specific/broad of a question, but are there 0ther examples of targets by the post-gangl.?

 

[sillyjoe]

And I'm not sure if this is too specific/broad of a question, but are there 0ther examples of targets by the post-gangl.?

Both the sympathetic nervous systems and the parasympathetic nervous system's post-ganglionic fibers all have "targets". By target's, I mean effector cells/end-organ/response organ. Many times they innervate the same organ but obviously have different responses.

Before looking at the schematic below know that often MANY make the mistake that the parasympathetic response is to "relax" and the sympathetic response is to "activate". This could not be further from the truth. To date, the best way I have heard to remember what the divisions are is that the PNS is "rest/digest/feed/breed" and the SNS is fight or flight. This is by no means absolute, but it can help you remember and eliminate choices.

Below is a schematic that shows the inputs/targets to both SNS and PNS:

 

[theyellowking]

Thank you so much! A much better diagram than EK's.