This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Unidirectional flow of a nerve impulse is at: 
Select and explain. 
A. Synapse, B. Axon, C. Dendrites, D. All of the above
A: Synapse
Answer: A: Synapse 
Explanation: A i.e. SynapseSynapses generally permit conduction of impulses in one direction only, from presynaptic to post-synaptic neurons. Any impulse conducted antidromically up the axons dies out because, post synaptical pa of neurons lack chemical synaptic vesiclesQ that are needed for synaptic transmission. Therefore an impulse arriving at the post synaptic membrane cannot release synaptic mediator.Axons can conduct impulse in both direction.Dendrites are found on the axon's endings and so behave in the same way as the axons i.e. bi-directional.