Nerves

[MIA6]

I want to ask some questions about nerves:
1.

Stimuli such as pressure, light, and sound do not travel along a nerve.

Does it mean like stimulus certainly will not travel along a nerve but it lets an impulse travels along a nerve, or specifically, axon?
2．

The electrical and chemical nature of an impulse is the same, regardless of the stimulus.

It means that whatever your stimulus's intensity, for instance, may be somebody stabs you or a tack pricks your finger, the impulse is the same?
3. Does Neuron have membranes? Is that myelin sheath?

Thanks for helping me out.

[mith]

the impulse is a all or nothing response, it either fires or does, there's no distinction there.

However, interpretation of the stimulus depends on which nerves are fired and frequency.

[Dr.Stein]

1. Only stimulus which is adequate (minimum at the treshold point) will be "converted" into electric signal or impulse, then will be processed as action potential thingy with "all or none" principle.

2. Yes the impulse is the same, the different thing is the kind of stimuli and the appropriate receptor for those stimuli, but the process of both is the same.

3. Neuron is cell, thus it has membrane. Myelin sheath is additional structure, which is only owned by neuron regarding to its function to transmit impulse.