Why do neurons have long axons but short dendrites?
Axons are used to transfer electrical signals from Point A to Point B.
Dendrites are for receiving electrical signals from different neuron cells via their respective Axons.

There are mainly two different types of Axons, insulated and non-insulated.

Insulated Axons allows extremely high velocity of electrical signals to propagate from Point A to Point B. Please note that insulated axons are not entirely insulated, the axons are only insulated at every given interval for a certain length (in measurement of distance). This forces the electrical signal to jump from one gap to another gap between insulation and result in extreme speed of electrical signal propagation down the axon.

Non-insulated axons still allow high velocity of electrical signal propagation but it is very much slower as compared to insulated axons. This is why when you have a stomach ache, its a slow and dull pain due to non-insulated axons which gives you prolonged pain signal. However, if you accidentally knock into a sharp object, you receive an instant sharp pain for a split second for you to react at that instant (Its a biological life saving function) due to insulated axons that gives you extreme speed of pain signal propagation.

On the other hand, dendrites are not built for signal transmitting but for signal receiving. Dendrites comes in different configurations, one such examples are your color sensory cells in your retina.

This is why dendrites are short while axons are long. They are configured for different purpose. Just a bit more information, electrical signal in biofluid are actually ionic current. Ionic current are different from electron current, the charge carrier are different. Lastly, electrical signal are generated due to electrochemical gradient on cellular level. When a certain membrane potential threshold is reached, action potential will be triggered and they resulted in the firing of electrical signal down the axons.

I hope you find these useful.

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