The body is in a constant state of readiness, prepared to react to changes both inside and out by producing certain sensations — such as burning when coming into contact with hot objects — and the ability to make the muscles contract or relax to elicit body movement. This is possible by a constant wave of electrical impulses that travel through the body to allow the brain and spinal cord to communicate with other areas of the body, otherwise known as the action potential. The action potential threshold is the point at which a neuron, or nerve cell reacts by firing a signal to the appropriate part of the body.
The action potential is an electrical voltage that is constantly surrounding the cells of the body, much like the high voltage wires found on telephone poles. Without this current of power the brain would be unable to communicate with the spinal cord, which, in turn, transmits the messages to the rest of the body. When a message is conveyed, the action potential threshold is activated which allows the neurons to “speak” to one another, thus initiating the proper response.
Action potential and the action potential threshold are essentially changes of the neurons polarization or electric field resulting in the nerve cells remaining at rest or firing to deliver impulses throughout the body. A neuron is composed of a nerve cell surrounded by a cell membrane with specialized projections or tail-like features called "dendrites" and "axons." Dendrites bring information in while axons send communications out. During periods of inactivity, positively charge ions, or electrically charged atoms or groups of atoms, exist just outside the axon membrane. Upon activation of a nerve cell, these positive ions seep through the membrane of the axon resulting in a state called depolarization. Once this change reaches a certain level, the action potential threshold is met and causes a firing of that particular neuron or grouping of nerve cells.
As these changes occur and the action potential threshold is met, the neurons can then convey messages back and forth between the brain, spinal cord, and the involved part of the body. Much like a telephone, in which a dial tone is present until phone number is dialed and the ability to connect to another line is activated, reaching the action potential threshold of a nerve cell results in the body reacting to changing circumstances. These changes can be inside the body, such as a reaction to an infection process, or outside the body, such as the muscles firing to avoid or remove a body part from a harmful stimulus, or to provoke movement of the body or body part.