The Receptor potential is the response of sensory cells to a stimulus and usually corresponds to a depolarization. It will also Generator potential called and is a direct consequence of the transduction processes with which the receptor converts a stimulus into excitation. This process is disturbed in receptor-associated diseases.
What is the receptor potential?
The sensory cells of the human body are called receptors. These are proteins or a protein complex to which signal molecules bind. This triggers signaling processes inside the cells. Receptors pick up signals from outside and process them into bioelectrical excitation. They 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 the unexcited state, the receptors hold a resting potential. This is a voltage difference based on an unequal distribution of sodium and potassium ions that separates the intra- and extracellular space. An incoming stimulus from the environment binds to the receptor proteins and allows 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 certain stimulus. Some authors differentiate the receptor potential and the generator potential. They understand the depolarization of a sensory neuron as a generator potential. For them, however, a receptor potential is a potential in the membrane of the receptor cell.
Function & task
The receptor potential arises as a result of the transduction process. This process corresponds to the conversion of stimulus energies into the body's own and therefore processable excitation.
In connection with this conversion, the concept of the signal cascade plays a major role. To a certain extent, the individual sensory cells follow different paths of stimulus processing and transduction. The steps of bonding, transformation, transmission and regeneration are common to them. The depolarization of the sensory cell is also a common step. The photoreceptors of the eye are an exception. Light, as an adequate stimulus, causes hyperpolarization in them.
The normal case, however, is depolarization. It takes place in relation to the respective strength of the stimulus received. Depending on the strength of the stimulus, changes in the basic tension between the intra- and extracellular space open the membrane-bound cation channels. In this way, a stimulus threshold-dependent action potential is generated in the affinity of the receptor.
Afference is the nerve tissue that specializes in the flow of information. The afferents are nerve tracts that feed excitations to the central nervous system.
The course of the receptor potential differs with the respective receptors. Typically, the potential is composed of a proportional and a differential component, so that the stimulus response of the receptors is proportional.
The receptor potential usually results from the opening of the membrane-bound sodium channels. They release sodium ions in the cell, which is understood as the actual excitation. The hyperpolarization of the photoreceptors, on the other hand, occurs when the channels are closed.
The receptor potential is not subject to an all-or-nothing law, but increases gradually with the strength of the stimulus. When a certain threshold value is reached and the threshold potential is thus exceeded, the sensory cell generates an action potential. Like almost all action potentials, that of the sensory cells also follows an all-or-nothing law and, as a rule, has no regenerative refractory period.
Illnesses & ailments
The group of receptor-associated diseases affects the excitation processes in receptor cells. This also has an impact on the receptor potential. In recent years, medical research has discovered various 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, process signals adequately or pass signals on. With other diseases from this group, the signal transduction can hardly be switched off or not switched off at all. Other mutations can generally leave certain receptors missing or incorporate them incorrectly into the membrane.
Most receptor-associated diseases 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 this inflammation, the internal structures of the receptor are destroyed and the sensory cells lose their functionality.
Examples from this group of diseases are myasthenia gravis and Lambert-Eaton syndrome. Myasthenia gravis is an autoimmune muscle neuronal disease. Lambert-Eaton syndrome is similar to this phenomenon, but is far more common than myasthenia gravis.
Diseases with receptor defects are differentiated according to their structural class. In the case of 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 an impact on the signal cascade of the receptors. In this case, their active ingredients work directly on receptors and mimic the function of the respective neurotransmitter in order to be able 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 activities.
