Question: How are potentials used?
About the article "Thermodynamics", section "Potentials".

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Local field potentials.
Local field potentials (LFPs) are electrophysiological signals that are related to the sum of all dendritic synaptic activity within a volume of tissue.
Recent studies suggest goals and expected value are high-level cognitive functions that can be used for neural cognitive prostheses. 
Thermodynamic potentials are different quantitative measures of the stored energy in a system.
Potentials are used to measure energy changes in systems as they evolve from an initial state to a final state.
The potential used depends on the constraints of the system, such as constant temperature or pressure.
For example, the Helmholtz and Gibbs energies are the energies available in a system to do useful work when the temperature and volume or the pressure and temperature are fixed, respectively.
The five most well known potentials are:where formula_1 is the temperature, formula_2 the entropy, formula_3 the pressure, formula_4 the volume, formula_5 the chemical potential, formula_6 the number of particles in the system, and formula_7 is the count of particles types in the system.
Thermodynamic potentials can be derived from the energy balance equation applied to a thermodynamic system.
Other thermodynamic potentials can also be obtained through Legendre transformation.
Spike potentials are one of the action potentials, which occur in electrical activity of smooth muscle contraction in animals.
These are true action potentials. 
Voltage-gated sodium ion channels (VGSC) are essential in producing and propagating action potentials.
Tetrodotoxin, a toxin found in pufferfish is able to block some VGSCs and therefore is used to distinguish the different subtypes.
There are three TTX-resistant VGSC: Nav1.5, Nav1.8 and Nav1.9.
Nav1.8 and Nav1.9 are both expressed in nociceptors (damage-sensing neurons).
It is known that Nav1.7, Nav1.8 and Nav1.9 are located in the DRG and play an important role in maintaining chronic inflammatory pain.
Nav1.8 α-subunit consists of four homologous domains each with six transmembrane spanning regions of which one is a voltage sensor.
Voltage clamp methods were used to show how action potentials in small diameter DRG cell bodies are shaped by TTX-resistant sodium channels.
Nav1.8 contributes the most to sustaining the depolarising stage of the action potentials in nociceptive sensory neurons by activating quickly and remaining activated after detecting a noxious stimuli.
Therefore, Nav1.8 is known to perform a key role in hyperalgesia and allodynia which are part of chronic pain.
Nav1.8 knockout mice studies have shown that the channel is associated with inflammatory and neuropathic pain.
Moreover, Nav1.8 plays a crucial role in cold pain.
Zimmermann "et al."
show that reducing the temperature from 30°C to 10°C slows the activation of VGSCs and hence decreases the current.
However, Nav1.8 is cold-resistant and is able to generate action potentials in the cold to carry information from nociceptors to the central nervous system (CNS).
Furthermore, Nav1.8-null mice failed to produce action potentials therefore indicating Nav1.8 is essential in the notion of pain in cold temperatures. 
Sensory evoked potentials (SEP), are recorded from the central nervous system following stimulation of sense organs (for example, visual evoked potentials elicited by a flashing light or changing pattern on a monitor; auditory evoked potentials by a click or tone stimulus presented through earphones) or by tactile or somatosensory evoked potential (SSEP) elicited by tactile or electrical stimulation of a sensory or mixed nerve in the periphery.
They have been widely used in clinical diagnostic medicine since the 1970s, and also in intraoperative neurophysiology monitoring (IONM), also known as surgical neurophysiology.
There are three kinds of evoked potentials in widespread clinical use: auditory evoked potentials, usually recorded from the scalp but originating at brainstem level; visual evoked potentials, and somatosensory evoked potentials, which are elicited by electrical stimulation of peripheral nerve.
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Long and Allen reported the abnormal brainstem auditory evoked potentials (BAEP) in an alcoholic woman who recovered from Ondine's curse.
These investigators hypothesized that their patient's brainstem was poisoned, but not destroyed, by her chronic alcoholism.