An action potential is able to travel along an axon at a speed of between 0.1 and 100m/s. So, in a few milliseconds a nerve impulse is able to travel from one region of the body to another. However, the speed rate is affected by three factors:

• Temperature: the higher the temperature the faster action potential can travel. This is why warm-blooded animals (homoeothermic) have quicker responses than cold-blooded animals (poikilothermic).
• Axon diameter: the bigger the diameter of the axon the faster the action potential travels. This is why organisms which live at cold temperatures, like marine invertebrates, have thicker axons in order to speed up their stimuli responses.
• Myelin sheath: myelin sheaths are only found in vertebrates. The sheath acts as insulation for the electrical impulse. The nodes of Ranvier, where there’s not myelin sheath present, are where the voltage-gated ion channels are located. The action potential then jumps from node to node, a process known as saltatory propagation, over large distances (about 1mm). This speeds up propagation by a big amount: in unmyelinated neurones the maximum speed is about 1m/s while in myelinated neurones an impulse can travel at about 100m/s.