The nerve get very sensative and active. . . I don't know because my hands shake even when I'm not nervous. I have a genetic condition commonly known as tremors.

It has something to do with the flow of adrenaline.

Your nervous system in control of the body functions you cannot consciously control (such as heartbeat, gut contractions, etc) is divided into two parts - sympathetic and parasympathetic. Normally the parasympathetic (often known as the "housekeeping" system) is dominant. What happens is that in times of emotional or physical stress, our sympathetic nervous system stimulation increases and is responsible for the changes that happen to our bodies during the "fight or flight" response. Amongst other signs, your pupils dilate to allow more light to enter the eye for improved vision, your heart rate and force of contraction increases to supply more blood to the muscles for a quick getaway from danger, you begin to breath heavier to increase oxygen supply and energy stores within your body are mobilised to provide your muscles with an instant supply of energy. Your nerves themselves stimulate the skeletal muscles to become more sensitive and coupled with the increased amount of chemical energy supplied to them, the muscles become excited and tense, and the individual fibres begin to reach electrical threshold producing visible shaking or twitches as they contract in groups.

itching to knock someone the f... out.

our hands also shake when we are very excited or very horny :) :)

I think it is a reaction from your nerves - From your mind down - I don't know if that makes any sense - I tried