Normal direction of signal transmission in neuron?

[ilovemedi]

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I'm confused in EK Bio, it says that the action potential begins in the axon hillock. But #81 (page 91) asks "Which of the flowing gives the normal direction of signal transmission in a neuron"?

Answer is: from dendrites, cell body, to axon. I thought it should be cell body (where axon hillock is), axon, then dendrites where it releases the neurotransmitters?

 

[inasensegone]

I'm confused in EK Bio, it says that the action potential begins in the axon hillock. But #81 (page 91) asks "Which of the flowing gives the normal direction of signal transmission in a neuron"?

Answer is: from dendrites, cell body, to axon. I thought it should be cell body (where axon hillock is), axon, then dendrites where it releases the neurotransmitters?

Dendrites receive a signal. The cell body is in between the dendrites and the axon. The part of the soma (cell body) before the beginning of the axon is the axon hillock. If the signal that makes its way to the axon hillock is not strong enough, no action potential will arise and the signal will not be propagated.

Edit: I didn't see your last sentence there. Neurotransmitters are released from the synaptic bulb (also called the terminal bouton), which is at the end of the Axon... not the dendrites. The dendrites receive a signal, the axon transmits it (if the signal is strong enough at the axon hillock)

 

[dyspareunia]

I'm confused in EK Bio, it says that the action potential begins in the axon hillock. But #81 (page 91) asks "Which of the flowing gives the normal direction of signal transmission in a neuron"?

Answer is: from dendrites, cell body, to axon. I thought it should be cell body (where axon hillock is), axon, then dendrites where it releases the neurotransmitters?

You have Neuron1 and Neuron2.

Neuron1 gets a signal from somewhere via Dendrite1. Then it travels to Soma1, then to Axon1, then to Dendrite2, then to Soma2, then to Axon2, and so on.

Conventionally we talk about the direction of signal transmission through a single neuron (i.e. dendrite1 -> soma1 -> axon1) and not through multiple neurons (i.e. axon1 -> dendrite2 -> soma2)

Dendrites receive a signal. The cell body is in between the dendrites and the axon. The beginning of the axon is the axon hillock. If the signal that makes its way to the axon hillock is not strong enough, no action potential will arise and the signal will not be propagated.

Edit: I didn't see your last sentence there. Neurotransmitters are released from the synaptic bulb (also called the terminal bouton), which is at the end of the Axon... not the dendrites. The dendrites receive a signal, the axon transmits it (if the signal is strong enough at the axon hillock)

The axon hillock is part of the soma, not the axon. There are also bouton en passants, which are located along the length of the axon and not just at the terminal. It depends on tissue type.

 

[inasensegone]

The axon hillock is part of the soma, not the axon.

True... thanks for the correction. I actually knew that it is technically part of the soma, but sloppily wrote that it is the beginning of the axon hillock for purposes of mapping signal propagation.

There are also bouton en passants, which are located along the length of the axon and not just at the terminal. It depends on tissue type.

Yeah but I'm pretty sure this is beyond the scope of the MCAT... good background knowledge, but if the MCAT tests this sort of thing, it will be discernible by process of elimination of wrong answers or by passage information.

 

[dyspareunia]

True... thanks for the correction. I actually knew that it is technically part of the soma, but sloppily wrote that it is the beginning of the axon hillock for purposes of mapping signal propagation.

Yeah but I'm pretty sure this is beyond the scope of the MCAT... good background knowledge, but if the MCAT tests this sort of thing, it will be discernible by process of elimination of wrong answers or by passage information.

If you're responsible for knowing that smooth muscle has gap junctions, then you're likely responsible for knowing that there is signal transduction at multiple locations on a given axon. Not sure though as I took the MCAT over a year ago now.

 

[inasensegone]

If you're responsible for knowing that smooth muscle has gap junctions, then you're likely responsible for knowing that there is signal transduction at multiple locations on a given axon. Not sure though as I took the MCAT over a year ago now.

Obviously I can't say with 100% certainty that such a topic (bouton en passant) won't be tested on the MCAT (given that esoteric questions are occasionally asked), however it would seem pretty unlikely. I would definitely say that the concept behind it is testable, because multi-unit smooth muscle seems fair game, but from what I learned these regions are referred to as varicosities. At any rate... thanks for dropping the term on us! Even if it isn't on our MCAT, it doesn't hurt to learn a bit more.

 

[ilovemedi]

Thanks @dyspareunia and @inasensegone for the insight! 🙂