TBR: Going Backwards in a Synapse

[justadream]

TBR Bio Book I page 52 #46

“As part of an experiment, a molecule is introduced at the synapses between heart muscle and nerve fivers of both the sympathetic and parasympathetic nervous systems. The molecule moves in a retrograde fashion through both of these divisions. By the time it reaches the next synapse, the molecule will have traveled through:”



Answer:

“An axon, moving a greater distance in the sympathetic nervous system than in the parasympathetic nervous system”


Two of the other answer choices have “DENDRITE” instead of “axon”.


Why aren’t both correct? When going backwards to reach the synapse between the pre and post ganglionic fibers, doesn’t this hypothetical molecule travel through BOTH an axon AND a dendrite?


I thought innervations go from Synapse ==> Dendrite ==> Axon ==> Synapse

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[ReggieNoble22]

Was also wondering about this, to me, in order to get from one synapse to the other the potential must travel through axon to dendrite to heart (retrograde).

 

[blackmarble]

no because the sympathetic and parasympathetic divisions are the efferent divisions of the ANS, I believe dendrites are more for afferent (sensory) divisions and act as sensory receptors to the environment, whereas the motor divisions probably act through direct transmission via axon/soma synapses.

 

[Hadi7183]

This question is also testing you whether you know the difference between preganglionic/postganglionic structures in sympathetic and parasympathetic systems. In both sympathetic and parasympathetic systems, the axon of postganglionic neuron synapses with the muscle. The difference is that in the latter, the postganglionic neuron is located much closer to the muscle and therefore has a shorter axon, whereas in the sympathetic system the postganglionic neuron is closer to the spinal cord and farther from the muscle. Thus, in the sympathetic system, the hypothetical substance needs to travel longer to reach the next synapse (which is b/w preganglionic and postganglionic neurons).