Imagine a long trail of dominoes running from your finger to the spinal cord in your back. When you touch a hot object, the messages this action produces in neurons is similar to the reaction that would happen if you knocked over the first domino of the set. After the first domino falls, each domino that follows it would be knocked over in turn. This process is similar to what happens between neurons. The message is carried from the fingertip touching the hot object all the way to the spinal cord. Neurons maintain a concentration of sodium and potassium ions; the openings present in membranes allow these ions to pass through. As the sodium and potassium gates open and then close, the electrical charge of the nerve cell changes and messages are transmitted along the neuron membrane.