The receptor potential is the response of sensory cells to a stimulus and generally corresponds to depolarization. It is also called generator potential and is a direct consequence of the transduction processes by which the receptor converts a stimulus into excitation. In receptor-associated diseases, this process is impaired.
What is the receptor potential?
The receptor potential is the response of sensory cells to a stimulus and generally corresponds to depolarization. Receptors are the sensory cells of the human body. They are proteins or a protein complex to which signaling molecules bind. Signaling processes are thus triggered inside the cells. Receptors receive signals from outside and process them into bioelectrical excitation. They thus translate stimuli from the environment into the language of the central nervous system. The receptors are highly specialized and are among the main instances of human perception. In an unexcited state, the receptors hold a resting potential. This is a voltage difference, based on an unequal distribution of sodium and potassium ions, which separates the intracellular and extracellular spaces. An incoming stimulus from the environment binds to the receptor proteins, causing the receptor to exceed its resting potential. This process is known as depolarization. The receptor potential is the membrane electrical response of sensory cells to a particular stimulus. Some authors differentiate the receptor potential and the generator potential. They understand the depolarization of a sensory neuron as a generator potential. A receptor potential, on the other hand, is for them a potential in the membrane of the receptor cell.
Function and task
The receptor potential arises as a consequence of the transduction process. This process corresponds to the conversion of stimulus energies into endogenous and therefore processable excitation. In connection with this transformation, the concept of signal cascade plays a major role. Individual sensory cells follow, to a certain extent, different paths of stimulus processing and transduction. However, the steps of binding, conversion, transmission and regeneration are common to them. Depolarization of the sensory cell is also a common step. The photoreceptors of the eye are an exception. Light evokes hyperpolarization in them as an adequate stimulus. The normal case, however, is depolarization. It occurs in relation to the respective strength of the stimulus received. Depending on the strength of the stimulus, the membrane cation channels open as a consequence of changes in the basic tension between intracellular and extracellular space. Thus, a stimulus threshold-dependent action potential is generated in the afferent of the receptor. Afferents are understood to be the nervous tissue specialized for the influx of information. Thus, afferents are nerve pathways that supply excitation to the central nervous system. The course of the receptor potential differs with the particular receptors. Typically, the potential is composed of a proportional and a differential component, so that the stimulus response of the receptors is a proportional response. The receptor potential generally results from the opening of the membrane sodium channels. They release sodium ions in the cell, which is understood as the actual excitation. In contrast, the hyperpolarization of photoreceptors arises with the closure of the channels. The receptor potential is not subject to an all-or-nothing law, but increases gradually with stimulus strength. When a certain threshold is reached and the threshold potential is thus exceeded, the sensory cell generates an action potential. Like almost all action potentials, that of sensory cells follows an all-or-nothing law and generally has no regenerative refractory period.
Diseases and disorders
The group of receptor-associated diseases affects the excitation processes in receptor cells. This also affects receptor potential. In recent years, medical research has discovered several receptor mutations. These mutations are now associated with a wide range of hereditary and somatic diseases. In receptor-associated diseases, the receptors are defective. For this reason, they are no longer able to bind to signal molecules, adequately process signals or transmit signals.In other diseases from this group, signal transduction can hardly be switched off anymore or not at all. Other mutations can cause certain receptors to be generally absent or incorrectly incorporated into the membrane. Most receptor-associated diseases, however, are not caused by the receptors themselves, but by autoantibodies. These autoimmune diseases attack the sensory cells with their autoantibodies and cause inflammation. In the course of these inflammations, the structures inside the receptors are destroyed and the sensory cells lose their ability to function. Examples from this group of diseases are myasthenia gravis and Lambert-Eaton syndrome. Myasthenia gravis is a muscle neuronal autoimmune disease. Lambert-Eaton syndrome is similar to this phenomenon, but is much more common than myasthenia gravis. Diseases with receptor defects are differentiated according to their structural class. In ion channel diseases, for example, the neuronal structure of the ion channels, and thus the biochemical excitability of the receptors, is disturbed. In addition to the group of receptor-associated diseases, psychotropic drugs can also have effects on the signaling cascade of the receptors. In this case, their active ingredients directly target receptors and mimic the function of the respective neurotransmitter in order to bind to the corresponding receptor. Other psychotropic drugs block the receptors for physiological neurotransmitters. The described effects of various psychotropic drugs are used in modern medicine specifically to influence receptor activity.
