Mechanoreception in humans includes all senses that are excited by mechanical stimuli. They are important for perception and the control of life processes.
What is mechanoreception?
Mechanoreceptors are specialized nerve cells that respond to specific mechanical stimuli. Mechanoreceptors are specialized nerve cells that respond to specific mechanical stimuli. They are located in various tissues, organs, and parts of the body and together comprise the mechanoreception system. Excitatory signals can be external (exteroception) or generated inside the body (interoception), and the types of mechanical stimuli can be pressure, stretch, tension, touch, movement or vibration. The stimulus-receiving structures of neurons are designed in such a way that the stimulus for which they are specialized causes a change in configuration at the cell membrane, which either directly or indirectly triggers an electrical potential (action potential) that travels via nerve conduction to the spinal cord or higher nerve centers. After reception and processing of the incoming electrical impulses, a stimulus response is sent from there to the corresponding organs with the initiation of an adequate reaction. These can be the same organs where the receptors are located or others. The density of receptors can be different in the same or comparable organs, depending on their importance for the perception and regulation of life processes. Many systems are constructed as a closed-loop system in which feedback occurs directly from the spinal cord to the organs of success after signal input.
Function and task
One task of all mechanoreceptors is to receive and transmit information to higher centers. In these, incoming data are processed and evaluated qualitatively and quantitatively. Depending on the strength of the stimulus and its importance to the biological system, they are either merely stored, perceived as a sensation, or a stimulus response occurs immediately with the goal of reducing or stopping the triggering factors. The response initiated via feedback is often a protective response. Stretch receptors exist in many different systems of the body. In the gastrointestinal and bladder walls, they are excited as filling increases, leading to a decrease in the feeling of hunger in the first case, triggering the laxative process in the second, and the urge to urinate in the third. In the tendon-muscle system, stretch receptors are located in the Golgi tendon organ and in the muscle spindle. The tension gauges of the receptors are connected in parallel with the muscle and tendon fibers and are excited when the muscle is lengthened. Here, they perform a typical protective function by causing the same muscle in which they are located to contract when the stretch threatens to become so great that it may cause injury. The muscle spindle is a highly complex receptor system, sometimes referred to in the literature as an organ within an organ. Although it is located in the muscle, it has independent contractile elements with which it can change the tension of the stretch receptor. In addition to registering changes in tension, this allows the sensitivity of the system to be regulated, depending on the motor demand. Joint receptors measure not only pressure but also the change in angle during movements of the bones belonging to the joint. Together with the muscle spindles, they form an important component of depth sensitivity, which enables the position of the whole body or of individual parts, movements and changes in movement and tension to be registered constantly and unconsciously. In our largest organ, the skin, there are a number of receptors on the surface, some of which also pick up mechanical information. The sense of touch provides information about the materials and substances with which the skin comes into contact. In addition to motor reactions, this can also trigger emotional sensations. In addition, there are also receptors that measure pressure and vibrations. They perform a protective function by providing information that leads to motor responses being initiated to eliminate or reduce the triggering stimulus, thereby preventing damage.
Diseases and disorders
Disorders of mechanoreception may have their cause either at the receptor itself or may be due to diseases in the areas of the central nervous system responsible for impulse processing.Peripheral nerve lesions lead to the fact that the reception of stimuli by the receptors still functions, but the transmission does not. No information then reaches the spinal cord or higher centers. Accordingly, no reaction or sensation can occur. A typical example of this is numbness in a certain area supplied by sensitive skin nerves. In the case of a herniated disc, the conduction of impulses close to the point of entry to the spinal column may be disturbed. In addition to complete numbness in the corresponding skin area (dermatome), there may also be sensory disturbances, such as tingling. Polyneuropathy is a disease in which the metabolism of the nerves is attacked, especially peripherally in the feet and arms. The protective insulation of the nerve pathways is increasingly broken down. Information first reaches the spinal cord in a reduced and slower way and finally falls away completely. In addition to skin sensitivity, the mechanoreceptors of the musculoskeletal system are particularly affected, leading to a gradual loss of depth sensitivity. Affected people do not feel their feet and no longer have any perception of which joint position they are in. For a time, this deficit can be compensated visually. The disease also affects the motor system in parallel, resulting in a double problem of perception, for example when walking. Diseases of the central nervous system such as multiple sclerosis or a stroke can also result in sensory deficits. In most cases, the reception and transmission of stimuli by the mechanoreceptors still functions, but the incoming signals cannot be processed or cannot be processed properly in the central nervous system. The consequences are similar to those of polyneuropathy, but usually much more complex. Not only peripheral areas but all areas of the body may be affected.
