Bio question help

[D.D.S.]

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Hey guys and girls I need your help and explanation for this question:

A rectifier is an electrical device that allows currrent to flow only in one direction. In human physiology, an analogous device is the:
A. Axon
B. Dendrite
C. Synapse
D. Schwann cell
E. Spinal nerve

The answer is C (synapse). I dont understand this since the question is asking about an electrical device, and during a synapse, isnt that a chemical (neurotransmitters) process? I would think the answer would be axon...

please explain....

Thanks.

 

[DDS4tehwin]

Synapses propagate only unidirectionally.

 

[D.D.S.]

but an action potential propagates unidirectional in an axon as well...

 

[jigabodo]

but an action potential propagates unidirectional in an axon as well...

That's what I was thinking. Not saying that synapse doesn't work unidirectionally, but this should also apply to AP due to axon's refractory period.

 

[D.D.S.]

and also the question refers to a rectifier being an "electrical" device so an axon would be a better answer choice since the action potential is propagating in the axon and an action potential is an "electrical" discharge...😕

 

[TimeforDAT]

where did you get this question? I think i've seen a question like this before? Kaplan?

 

[DDS4tehwin]

but an action potential propagates unidirectional in an axon as well...

i vaguely remember that there are some action potentials which can go backwards

 

[Decan]

I wouldve said axon as well...where did you get this question?

 

[D.D.S.]

This question came from the biology subject test 4 from kaplan. #12.

 

[tinman831]

If a synapse is placed in the middle of an axon and a stimulus is applied, technically, the action potential can travel in both directions away from the middle. There would not be anything physically limiting the action potential from being conducted both ways.

 

[airsimon]

OK I'm currently a Senior studying Neuroscience and to me, axon would be the only logical answer. Does Kaplan give you an explanation? It might be a typo.

 

[D.D.S.]

This is kaplan's explanation:
The synapse is a small space between an axon and dendrite of two neurons. After stimulation, the axon will release a neurotransmitter across this cleft, which will diffuse and bind receptors on the dendrite of the next
neuron. The neurotransmitter can only be released by the axon and can only be received by the dendrite and is therefore similar to a rectifier. Answer choice A is incorrect because the axon is only the section of the neuron
away from the cell body while answer choice B is incorrect because the dendrite is the section of the neuron going toward the cell body. Answer choice D is incorrect because Schwann cells are insulating cells of the
neurons. Answer choice E is incorrect because a spinal nerve is a bundle of nerves where they enter and exit
the spinal cord.

 

[Decan]

If a synapse is placed in the middle of an axon and a stimulus is applied, technically, the action potential can travel in both directions away from the middle. There would not be anything physically limiting the action potential from being conducted both ways.

Can you please elaborate further b/c that doesnt make sense to me...a synapse is a physical gap between the axon terminal of the pre-synaptic cell and the membrane of the post synaptic cell. You cant really place it in the middle of an axon because you would then break the neuron.

The only answer that makes sense to me is axon because it has unidirectional flow (due to the relative refractory period).

 

[jigabodo]

Answer choice A is incorrect because the axon is only the section of the neuron
away from the cell body

Is it just me, or is the answer not making sense at all?

Seriously though, the release of neurotranmistter at the synapse cannot really be catagorized as electrical stimulation since they are chemicals.

And w/o refractory period, any nerve impulse will just travel back and forth and never cease and our bodies wont be able to function.

 

[Lonely Sol]

If a synapse is placed in the middle of an axon and a stimulus is applied, technically, the action potential can travel in both directions away from the middle. There would not be anything physically limiting the action potential from being conducted both ways.

I agree, axon may very well be used to travel impulse in both direction, however looking at the choices only synapse move in a true one-way direction because there are no receptors to carry out an axon potential in pre-synaptic membrane, so action potential could go in reverse direction, plus it would pointless to do so.

An example of bidirectional axon flow is an herpesvirus, which conducts signal on both direction!

 

[tinman831]

Can you please elaborate further b/c that doesnt make sense to me...a synapse is a physical gap between the axon terminal of the pre-synaptic cell and the membrane of the post synaptic cell. You cant really place it in the middle of an axon because you would then break the neuron.

The only answer that makes sense to me is axon because it has unidirectional flow (due to the relative refractory period).

What I mean by synapse, is a source of stimulation. If you stimulate the middle of an axon, technically, an action potential can occur in both directions. While this does not occur in humans, due to refractory periods, its theoretically possible. A synapse is strictly one direction. Vesicles release neurotransmitter on the presynaptic side and there are receptors on the post synaptic side. You do not find receptors on the presynaptic side so the action potential can't go in reverse.

 

[AaBbZz]

Ok so I was reading Kaplan notes and directly from the book it says
"Impulses known as action potentials travel the length of the axon in only one direction and cause neurotransmitter to be released at the axon terminal"

I think the correct answer is definately the Axon, even with all the other post this question is directly asking you to compare it to HUMAN PHYSIOLOGY no any other organism!

Also it is asking for ELECTRICAL which should be the biggest clue for axon

Even though it doesn't happen to much Kaplan does get practice questions wrong I know this for a fact since when i took the class the made corrections to my tests and books.

This is just my opinion but I still think the answer is AXON and for most people i also think that this is your gut feeling which in most cases is usally right

 

[pluginchugin]

yea most of kaplan's answers are extremely messed up. has anyone did their reading comp practices? seriously... kaplan needs to revise they're entire system of practice questions.

 

[jdoc04]

Decan is correct. This is a trick question is does not state as to how the potential is generated. If you stimulate an axon in the middle of its length an electrical potential will propagate in BOTH directions. Why?? B/C the initial event beginning in the middle of the axon does not have a refractory period following it which makes normal transmission UNIDIRECTIONAL as we are all taught. Note that there are BOTH chemical and electrical synapses. The electrical synapses are called Connexons. (Sp?)

 

[hokie4life]

wait i'm confused then so what is the right answer? I would've said axon originally too but now after reading all this I can see why you would wanna say synapse, esp. cuz of what tinman831 vbmenu_register("postmenu_5347997", true); said

 

[tinman831]

If the answer was axon, why wouldn't dendrite also be correct? Current flow is the same in both axon and dendrite.

The question asks what in human physiology is analogous to a rectifier, that is, what inside the human body is unidirectional. An axon is capable of bidirectional flow (it just doesn't happen inside the human body). A rectifier is not capable of bidrectional flow. A synapse does not have bidirectional flow also.

Whether it is chemical current or electrical current is irrelevant. It simply asks what is analogous to a rectifier. A one way street is analagous to a rectifier, as well, even though one pertains to electrical current whereas the other pertains to cars.

Just my 2 pennies

 

[PD3]

Just to mess with everyone a little bit, there are neurotransmitters that are believed to travel from post synaptic cell to presynaptic cell. They are endocabbabinoids, http://en.wikipedia.org/wiki/Cannabinoids. Of course, these are not the norm.