Why is the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron but not the reverse?

Question

(i) Why is the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron but not the reverse? 

(ii) Sameer was studying in his room. Suddenly he smells something burning and sees smoke in the room. He rushes out of the room immediately. Was Sameer’s action voluntary or involuntary? Why?

Answer 1

(i) When an electrical signal reaches the axonal end of a neuron, it releases a chemical substance. This chemical diffuses towards the dendrite end of next neuron where it generates an electrical impulse or signal. Hence, the electrical signal is converted into a chemical signal at the axonal end. Since these chemicals are absent at the dendritic end of the neuron, the electrical signal cannot be converted into chemical signal. 

(ii) Sameer’s action was voluntary because rushing out of the room was under his conscious control. The smoke and smell were perceived by the receptors in the sense organs and signals are sent to the brain. The brain, then sent signals to the effector organs, i.e., the muscles, to move out of the room.