Epicritic sensitivity is a perceptual system of the skin and is also called tactile acuity or fine perception. It is closely related to proprioception. Disorders of epicritic sensitivity often have peripheral or central nerve damage as their cause.
What is epicritic sensitivity?
Epicritic sensitivity is a perceptual system of the skin and is also called tactile acuity or fine perception. The human skin sense has different perceptual qualities, which are summarized as surface sensitivity. One of them is epicritical sensitivity. As such, the discriminative perceptions of vibration, pressure, and touch are understood, also known as fine perception. In addition, epicritical sensitivity involves perceptions of the proprioceptive sense of position and is thus involved in both the interoception of stimuli internal to the body and the exteroception of external stimuli. Epicritical sensitivity works with different sensory cells that translate a stimulus into the language of the central nervous system. The epicritical receptors are either exteroceptors or interoceptors. The exteroceptors of epicritic sensitivity are predominantly mechanoreceptors for obtaining information about the localization or fine-tuning of a touch. Relevant as epicritical interoceptors are proprioceptors such as the muscle spindles and tendon spindles, which serve to obtain information about muscle and joint position. Protopathic sensitivity must be distinguished from epicritic sensitivity. This second perceptual quality of the skin sense provides information about temperatures and pain via thermoreceptors and nociceptors and is also called predominantly exteroceptive gross perception. As part of tactile perception, epicritical sensitivity, in contrast to protopathic sensitivity, refers to the ability to perceive spatially closely adjacent touch stimuli as individual stimuli. Fine perception plays a role in both tactile and haptic perception, in the sense of passive and active tactile perception.
Function and task
The epicritic perceptual system is also called the discriminative system of the skin sense. In contrast, the protopathic system of the skin sense corresponds to a protective system. Epicritic perception can be broken down into passive touch perception and active exploratory perception. All proprioceptive structures of the system are passive touch perception structures. The first place for the perception of epicritical information are the receptors. In this context, mechanoceptors such as the pressoreceptors and baroreceptors are distinguished from proprioceptors such as the muscle spindles. Mechanoceptors are primarily concerned with pressure perception. Proprioceptors are responsible for self-awareness. Beroreceptors, for example, are located in the wall of blood vessels and are involved in enteroceptive regulation of blood pressure. Mechanoreceptors are mainly divided into SA, RA and PC receptors. The most important SA receptors are Merkel cells, Ruffini corpuscles, and pinkus Iggo tactile discs for pressure perception. Major RA receptors are the Meissner corpuscles, hair follicle sensors, and Krause end pistons for touch perception. PC receptors for vibration perception are mainly known to be the Vater-Pacini corpuscles and the Golgi-Mazzoni corpuscles. In connection with proprioception, enteroceptive receptors are distinguished from purely proprioceptive receptors. Enteroceptive epicritic receptors in the bladder, gastrointestinal tract or cardiovascular system regulate automatically controlled bodily processes such as the urge to urinate, the urge to defecate, the cough reflex or the filling of the atria. The transmission of all epicritical information occurs for all exteroceptive stimuli via the posterior cord pathways of the spinal cord. In contrast, the protopathic receptors of the cutaneous sense transmit their information to the cerebellum via the tractus spinocerebellaris anterior or tractus spinocerebellaris posterior|posterior. The posterior cord tracts as the afferent information pathway of epicritic sensibility run uncrossed. The fasciculus gracilis is responsible for information involving the lower extremities. The fasciculus cuneatus, on the other hand, conducts the epicritic information of the upper extremities.The first neuron undergoes a switch to the second neuron in the nucleus gracilis or nucleus cuneatus of the brainstem. After this switch, the tracts continue as lemniscus medialis and cross within the decusatio lemniscorum. In the thalamus, they are switched to a third neuron, which then transports the epicritical information to the postcentral gyrus. As part of tactile perception, epicritical sensitivity is determined in terms of tactile acuity using two-point discrimination thresholds. In young people, the tactile acuity of fine perception is about 1.5 millimeters at the fingertip. In older people, it is sometimes only four millimeters. At the back, the tactile acuity of fine perception is physiologically lowest and amounts to a few centimeters.
Diseases and complaints
The most important task of the epicritic system is the evaluation and differentiation of tactile impressions and touch impressions. Thus, disorders of the epicritic system are expressed predominantly in the inability to discriminate touch or tactile sensations. All disorders of surface sensibility are among the most frequently due to damage to peripheral or central nerves. A lack of sensory integration can also be a factor in epicritical sensitivity disorders. A sensory integration disorder is caused by predisposition and manifests itself in the inability to combine different sensory impressions. On the other hand, it can result from a lack of physical practice in childhood. The ability to combine different sensory impressions is particularly crucial for near senses such as the epicritical system and can be increased if necessary if there is a disposition. Epicritic sensitivity disorders manifest as either hyperesthesia or anesthesia. Hyperesthesia corresponds to increased perception or hypersensitivity to touch stimuli and may be painful in degree. Hyperesthesia often results from acute or chronic irritation of nerve structures, such as after surgery or other procedures. Affected persons often show tactile defensiveness, which manifests itself in the avoidance of touch. The opposite phenomenon is anesthesia, which is equivalent to insensibility. Anesthesias with local limitation are seen, for example, in peripheral polypathies of a particular part of the body, as may be caused by poisoning, diabetes, or certain infections. Just as often, local anesthesias are due to central nervous damage in the setting of a neurologic disease such as multiple sclerosis, stroke, or spinal cord infarction. Traumatic damage to the central nervous system is also a possible cause. The same applies to tumor diseases of the central nervous system.
